[Palaeontology, Vol. 48, Part 4, 2005, pp. 793–816]
SKULL MORPHOLOGY AND PHYLOGENETIC
RELATIONSHIPS OF A NEW DIMINUTIVE
BALAENID FROM THE LOWER PLIOCENE
OF BELGIUM
by MICHELANGELO BISCONTI
Dipartimento di Scienze della Terra, Università di Pisa, via Santa Maria 53, 56126 Pisa, Italy; e-mail: bisconti@dst.unipi.it
Typescript received 26 November 2003; accepted in revised form 10 May 2004
Abstract: A new small balaenid is described and compared
to all fossil and living balaenid taxa. The specimen represents
a new genus and species and is named Balaenella brachyrhynus. It was discovered in the Lower Pliocene of Kallo (northwest Antwerp, Belgium) and adds new information on the
diversity and evolution of Balaenidae. Based on both comparative morphology and phylogenetic analysis, Balaenella
brachyrhynus is morphologically closer to the genus Balaena,
including the living Greenland Bowhead whale (B. mysticetus), and two Pliocene species (B. montalionis and B. ricei)
from central Italy and the eastern USA. Balaenella brachyrhynus has very short nasals, a short rostrum relative to the total
skull length and a horizontal supraoccipital. A cladistic treat-
In zoological textbooks, balaenids are usually regarded as
gigantic, slow-swimming Mysticeti (Mammalia, Cetacea)
with an arched rostrum and long baleen (Ridgway and
Harrison 1985; Berta and Sumich 1999), but it is often
forgotten that small and more streamlined forms have
flourished during their evolutionary history. Small balaenids are represented by a conspicuous and widespread
fossil record. They occur in the Upper Miocene–Lower
Pliocene of California (eastern Pacific; Barnes 1977), and
in Pliocene sediments of Belgium (north-east Atlantic;
Van Beneden 1880, 1878), Italy (central Mediterranean;
Trevisan 1941; Pilleri 1987; Bisconti 2000), Japan (western
Pacific; Excavation Research Group for the Fukagawa Fossil Whale 1982), and eastern USA (western Atlantic;
Whitmore 1994). Despite their worldwide occurrence,
only a few species have been described and figured in
detail; these are: the Japanese Balaenula sp. (Excavation
Research Group for the Fukagawa Fossil Whale 1982), the
Italian Balaenula astensis (Trevisan 1941; Pilleri 1987; Bisconti 2000) and, to some extent, the Belgian Balaenula
balaenopsis (Van Beneden 1878, 1880).
The small balaenids are usually grouped within
the genus Balaenula Van Beneden, 1880. Balaenula is
ª The Palaeontological Association
ment of 81 morphological character states scored for 10
balaenids and nine non-balaenid cetaceans revealed that the
other small balaenids generally included in the genus Balaenula (including Balaenula astensis, B. balaenopsis and a Pliocene Balaenula sp. from Japan) are closer to the living genus
Eubalaena (the Right whale). As the new skull is so different
from the nominal Balaenula species, and as it is more closely
related to Balaena than to Eubalaena, it is concluded that a
small body size was a common condition in different Balaenidae clades.
Key words: Balaenula, Balaenidae, Belgium, Cetacea, Mysticeti, Phylogeny, Pliocene.
based on a fragmentary skull and associated skeleton
but unfortunately an unambiguous character-based diagnosis of the genus has been lacking until recently (Bisconti 2003a). Abel (1941) re-assessed some Belgian
material pertaining to Balaenula and provided a reconstruction of the type skull (Van Beneden did not designate any holotype material). However, some
morphological details (such as the dorsal surface of the
supraoccipital, the relationships of maxilla and frontal,
the morphology of the distal portion of the rostrum,
and part of the architecture of the temporal fossa) are
definitively lost and their reconstruction is based on
inference only.
In his original descriptions of the Balaenula type skull
(namely Balaenula balaenopsis), Van Beneden (1880,
1878) also discussed the morphology of periotic and
tympanic bones. Unfortunately, it is not certain that
these bones belong to the type skull because they were
found disassociated from it (Van Beneden 1880, 1878),
and the features of the petrosal are so different from
what is observed in other balaenids that it is likely that
it does not belong to a balaenid at all (but see Bisconti
2003a).
793
794
PALAEONTOLOGY, VOLUME 48
New discoveries made during the twentieth century
provided materials for the detailed descriptions of two
well-preserved skulls and associated petrotympanic complexes of small balaenids from Italy and Japan (Trevisan
1941; Excavation Research Group for the Fukagawa Fossil
Whale 1982). The new specimens were assigned to the
genus Balaenula based on the small size of the crania. Bisconti (2000) assessed the phylogenetic relationships of the
Italian specimen (Balaenula astensis) on cladistic grounds
and found that it was close to the Belgian Balaenula
balaenopsis; however, the Japanese Balaenula sp. was not
included in the ingroup and its phylogenetic position is
still unclear. Bisconti (2000) found differences between
the Italian and the Belgian species in the architecture of
the temporal fossa and the brain size, and found a
weakly supported relationship between Balaenula astensis,
B. balaenopsis and the living Right whales (Eubalaena) to
the exclusion of the extant and fossil species of Balaena
that were known at that time. However, the low resolution of his cladograms demands a new and comprehensive study in order to fix systematic relationships among
the Balaenidae.
In a review of the evolutionary history of balaenids,
Bisconti (2003a) provided redescriptions of several fossil
taxa from Europe and emended some morphological
diagnoses including that of Balaenula. He also furnished
a redescription of some type materials belonging to the
Belgian Balaenula balaenopsis. Furthermore, he updated
the systematics of fossil Balaenidae and stated that, currently, three species belong to Balaenula: the Italian
B. astensis, the Belgian B. balaenopsis and an unnamed
Balaenula sp. from Japan. The diagnosis of Balaenula is
now unambiguous and mainly based on the orientation
of the squamosal (in Balaenula it is directed anteriorly),
the position of the cranio-mandibular joint (which, in
Balaenula, is located under the orbit), and the height
of the exoccipital relative to the orbit (which, in
Balaenula, is very low).
A new small balaenid is described in this paper based on
a fairly well-preserved skull. The specimen is described
and compared to the other giant and small, living and fossil balaenids. The phylogenetic position of the new skull is
explored by means of a cladistic study of the best-preserved fossil balaenids, together with representatives of the
living taxa. Based on the phylogenetic results and the comparative analysis, it is concluded that the skull shows morphological features that distinguish it from the Italian,
Belgian and Japanese small balaenids at generic level.
Indeed, it represents a lineage unrelated to Balaenula,
being closer to the giant Balaena (the Greenland Bowhead
whale). The skull documents an unsuspected diversity
among the small balaenids and, based on its phylogenetic
position, suggests that in the past few million years a small
size was a common condition in different balaenid clades.
T E X T - F I G . 1 . Location of Antwerp and some of the principal
towns of Belgium (west of the River Mose), southern Holland
(north of the River Mose) and north-west Germany (south and
east of the River Rhine); the black rectangle indicates the
discovery area.
The new balaenid was found by E. T. H. Van Tuiyll
in 1974 at Kallo, north-west Antwerp (Belgium; Textfig. 1), during the construction of the First Channel dock
(Eerste Kanaaldok), 18 m below sea level. The First Channel dock is one of a series of channels connecting Antwerp with the Schelde River (and indirectly with the
North Sea). The specimen was displayed in Van Tuiyll’s
palaeontological collection until March 2001, when the
whole collection was donated to the Natuurmuseum
Brabant in the town of Tilburg, Holland.
MATERIAL AND METHODS
Institutional abbreviations. MSNT, Museo di Storia Naturale
e del Territorio, Università di Pisa, Pisa, Italy; MGP, Museo
Geopaleontologico G. Capellini, Università di Bologna, Bologna,
Italy; IRSN, Institute Royal des Sciences Naturelles, Bruxelles,
Belgium; NMB, Natuurmuseum Brabant, Tilburg, The Netherlands; SMNS, Staatliches Museum für Naturkunde, Stuttgart,
Germany; USNM, United States National Museum of Natural
History, Smithsonian Institution, Washington, DC, USA; ZMA,
Instituut voor Systematiek en Populatiebiologie ⁄ Zoölogisch
Museum, Amsterdam, The Netherlands; ZML, Zoölogisch
Museum, Leiden, The Netherlands.
Anatomical terms and abbreviations. The anatomical terminology describing the general features of the cetacean skull follows Kellogg (1965, 1968a). Petrosal terminology is in accord
with Geisler and Luo (1996, 1998) and Luo and Gingerich
(1999); tympanic terms are from Oishi and Hasegawa (1994),
Luo (1998) and Luo and Gingerich (1999). Abbreviations as
follows: an, antorbital notch; ap, anterior process of petrosal;
apat, anterior pedicle for the articulation with the tympanic;
exocc, exoccipital; fm, foramen magnum; ip, infraorbital process of the maxilla; irfr, interorbital region of the frontal; lp, lateral protrusion of the lambdoidal crest; lpap, lateral projection
of the anterior process of the petrosal; lsc, lateral squamosal
BISCONTI: DIMINUTIVE PLIOCENE WHALE
crest; mx, maxilla; mxf, maxillary foramen; n, nasal; nf, narial
fossa; oc, occipital condyle; p, parietal; pbsf, posterior border
of the stylomastoid fossa; pc, pars cochlearis; pgl, postglenoid
process; plc, posterolateral corner of the pars cochlearis; pmx,
premaxilla; ppp, posterior process of the petrosal; ow, oval
window; si, sutura interfrontalis; soc, supraoccipital; sop, supraorbital process of frontal; ttg, tensor tympani groove; zp,
zygomatic process of squamosal; VII-g, groove for the facial
nerve.
Sources of comparative data
Eubalaena glacialis. MSNT 264: skeleton and left petrotympanic; ZML without inventory number (abbreviated w.i.n.):
skeleton and both petrotympanics; USNM 267612, 3339990,
23077, 301637: skulls and petrotympanics. Based on molecular
analyses, Rosenbaum et al. (2000) and Malik et al. (2000)
proposed that Eubalaena should comprise at least three different living species. However, morphological features useful to
distinguish these three supposed species are not currently
available (Bisconti 2002), and for that reason here I
accept the traditional, morphological definition of the genus
Eubalaena (Cummings 1985; Mead and Brownell 1993), and
consider that at present the genus includes two geographically
distinct species, Eubalaena australis and E. glacialis. General
descriptions and illustrations can be found in Cuvier (1823),
Van Beneden and Gervais (1880), True (1904) and Cummings
(1985).
Eubalaena belgica. Type material described by Abel (1941) and
Plisnier-Ladame and Quinet (1969) as Balaena belgica. The
taxon is represented by the IRSN holotype skull, Ct.M. 879a–f
(including portions of squamosals, maxilla and frontal).
McLeod et al. (1993) suggested that this form is so similar to
Balaenula balaenopsis in the morphology of the zygomatic
process of the squamosal that it should be referred to Balaenula as the new combination Balaenula belgica. I examined the
type skull and confirmed this observation, but it should be
noted that the type skull of this taxon is very large and
heavy, differing from the small, slender forms belonging to
Balaenula. Moreover, in this large Belgian species, the lateral
borders of the supraoccipital are parallel whereas they are
anteriorly convergent in Balaenula astensis and the Japanese
Balaenula sp.; therefore, the morphology observed in the Belgian species resembles Eubalaena glacialis and not Balaenula.
A slender zygomatic process of the squamosal was described
by Nishiwaki and Hasegawa (1969) in a Pleistocene Eubalaena
glacialis from Japan; therefore this feature does not appear to
be useful for generic diagnosis. Bisconti (2000, 2003a) suggested that Balaena belgica should belong to Eubalaena based on
the morphology of the supraoccipital, a strong temporal
ascending crest on the supraorbital process of the frontal, and
the angle between rostrum and frontal.
Balaena mysticetus. IRSN 1532: skeleton; ZML 1680, 3997,
2563, 2001, two ZML w.i.n. (both petrotympanics labelled ‘Balaena japonica’), and ZML w.i.n. (right petrotympanics); USNM
795
257513: skull. Descriptions and illustrations can be found in
Cuvier (1823), Van Beneden and Gervais (1880), Reeves and
Leatherwood (1985) and Burns et al. (1993).
Balaena montalionis. MSNM MC CF31 holotype skull (see
Capellini 1904; Pilleri 1987; Bisconti 2000, 2003a for descriptions
of the specimen).
Balaena ricei. Westgate and Whitmore (2002).
Balaena primigenius. Type material described by Van Beneden
(1880, 1878), held by IRSN and represented by Ct.M. 887
(left petrosal), Ct.M. 886, Ct.M. 884 (both right tympanic
bullae). Bisconti (2003a) re-assessed the type materials, concluding that the taxon is too poorly known to receive a scientific
name; therefore, Balaena primigenius is a Balaenidae gen.
indet.
Balaenula balaenopsis. Type material described by Van Beneden
(1880, 1878), held by IRSN and represented by Ct.M. 858a–b
(right petrosal), Ct.M. 853d (posterior process of petrosal),
Ct.M. 859–863 (tympanic bullae), Ct.M. 865a–b, 867a–c, 868,
869a–b (cervical vertebrae). Additional material held in MGP is
represented by a skeleton from Poggio alle Talpe including both
petrotympanics (central Italy; 1CMC29 ⁄ 8929; Capellini 1877;
Portis 1883).
Balaenula astensis. MSNM MC CF35 holotype skull and associated petrotympanics (see Trevisan 1941; Pilleri 1987; Bisconti
2000, 2003a for descriptions of the specimen).
Japanese Balaenula sp. Excavation Research Group for the
Fukagawa Fossil Whale (1982).
Balaenotus insignis. Type material described by Van Beneden
(1880, 1878), held by IRSN and represented by Ct.M. 832,
833a–b (both specimens are right petrosals), Ct.M. 834, 835
(both specimens are tympanic bullae), Ct.M. 836a–c (a is a
distal fragment of right supraorbital process of frontal, b and
c are rostral elements: a fragment of premaxilla and a proximal portion of maxilla), Ct.M. 837 (fragment of left squamosal), Ct.M. 838 (fragmentary supraorbital process of the
frontal), Ct.M. 840, 841a–b, 842a–b, 844a–b (cervical vertebrae), Ct.M. 850 (left scapula) and Ct.M. 856 (left fragment of
mandibular condyle). All these materials have been redescribed
by Bisconti (2003a). Additional material is held in MGP
(Capellini 1877; Portis 1883): the Poggiarone skeleton
(1CMC23 ⁄ 8923, 26 ⁄ 8926, 22 ⁄ 8922), the cast of a right petrosal from Pieve di Santa Luce (near Pisa, central Italy,
1CMC87 ⁄ 8987), the cast of a right petrosal from Monte Aperto (near Siena, central Italy, 1CMC ⁄ 8987). Balaenotus is a
problematic genus. It was based on a very incomplete skull,
petrotympanics and some postcranial bones by Van Beneden
(1880, 1878); however, this poor material is diagnostic at the
genus level (see Bisconti 2003a); therefore, in this work the
name Balaenotus insignis is retained.
Morenocetus parvus. Cabrera (1926).
796
PALAEONTOLOGY, VOLUME 48
SYSTEMATIC PALEONTOLOGY
Class MAMMALIA Linnaeus, 1758
Order CETACEA Brisson, 1762
Suborder MYSTICETI Cope, 1891
Family BALAENIDAE Gray, 1825
Genus BALAENELLA gen. nov.
Text-figures 2–7
Derivation of name. Balaena, Latin name for the Greenland
Bowhead Whale; -ella, Latin, diminutive suffix indicating a form
smaller than Balaena.
Type species. Balaenella brachyrhynus sp. nov.
Diagnosis. Balaenella brachyrhynus belongs to the family
Balaenidae owing to the following features: maxilla transversely compressed in its anterior three-quarters, rostrum
highly arched, supraoccipital extending anteriorly to the
orbit, supraorbital process of the frontal gently descending
from the interorbital region, parietal not exposed on the
cranial vertex, squamosal mainly developed along the
dorsoventral axis, lateral squamosal crest forming a strong
anterior convexity, triangular-shaped lateral projection of
the anterior process of the petrosal, posterodorsal corner of
the stylomastoid fossa rounded in dorsal view and far from
A
B
C
D
E
T E X T - F I G . 2 . Balaenella brachyrhynus holotype skull (NMB 42001). A, right lateral view. B, right premaxilla. C, left premaxilla.
D, left lateral view. E, anterior view. Scale bar represents 200 mm.
BISCONTI: DIMINUTIVE PLIOCENE WHALE
the posterior wall of the pars cochlearis, long and shallow
stylomastoid fossa, tympanic bulla dorsoventrally compressed, tympanic cavity shallow. It shares the following
features with Balaena: supraorbital process of the frontal
and lateral process of the maxilla posteriorly orientated so
that a continuous arch is developed by rostrum and frontal,
squamosal posteriorly orientated, posterior wall of temporal fossa observed when the skull is in lateral view, infraorbital plate absent laterally (feature figured by Cuvier
1823, pl. 25). The following features are exclusively diagnostic of Balaenella brachyrhynus: skull length slightly more
than 1000 mm, length of rostrum approximately 50 per
cent of the total skull length, nasal bones about 60 per cent
shorter than nasals of giant balaenids (Balaena and
Eubalaena) and about 75 per cent shorter than nasals of
Balaenula astensis, nasal bones lacking the anterior notch;
nasal bones forming a triangular complex displaying an
anterior apex, anterior two-thirds of supraoccipital horizontal, rostrum triangular in dorsal view, lateral process of
the maxilla strong.
Balaenella brachyrhynus sp. nov.
Derivation of name. Greek, brachy, little; rhynus, nose, denoting
a small Balaena with a little nose, and the marked reduction of
the nasal bones of the holotype skull.
Holotype. Specimen 42001, Natuurmuseum Brabant, Tilburg,
Holland. The specimen will be referred to as NMB 42001 or the
Tilburg skull in the text.
Type locality and horizon. The specimen was found during the
construction of the First Channel dock (Eerste Kanaaldok) at
T E X T - F I G . 3 . A, right side of the holotype skull (NMB 42001)
as preserved. B, left side of the holotype skull as preserved. The
scale bar represents 200 mm. See text for explanation of
labelling.
797
Kallo (north-west Antwerp, Belgium; Text-Fig. 1), 18 m below
sea level in the Zanden van Kattendijk (Kattendijk Sand) Formation. Janssen (1974) and Nuyts (1990) provided data on
the fossil content, biostratigraphy and lithostratigraphy of the
deposits near Kallo. The specimen was found in what Nuyts
(1990) described as clay, bioturbated at the top, infilled with
greyish green sands. The clay belongs to the Kattendijk Formation and is Early Pliocene in age based on its foraminiferal
content. The Kattendijk Formation contains a foraminiferal
association that is typical of the BFN 4 (Florilus boueanusMonspeliensina pseudotepida Assemblage Zone; Nuyts 1990).
Janssen (1974) stated that the Kattendijk Formation is Scaldisian or ‘Kattendijkien’ in age; Hoedemakers and Marquet
(1992) correlated the ‘Kattendijkien’ to the Mediterranean
Tabianien. The latter is now completely incorporated in the
Zanclean (Monegatti and Raffi 1996), i.e. Early Pliocene
(2Æ5–5Æ3 Ma; Sprovieri 1992; Rio et al. 1994), and this is the
age proposed for NMB 42001.
Diagnosis. As for genus.
Description
The skull is substantially complete; it lacks dentaries, the right
petrotympanic complex, the anterior end of maxillae, right orbit,
jugals, lacrimals and some portions of the squamosals. The premaxillae are largely preserved but are detached from their natural position by the collector. Taken as a whole, this skull is one
of the best-preserved balaenid specimens in the world. Measurements of skull and petrotympanic complex are given in Tables 1,
2, respectively. The skull as preserved is illustrated in Textfigures 2, 3; a reconstruction of the skull is presented in Textfigure 4.
Rostrum: maxilla, premaxilla, nasal. The left maxilla is almost
complete, lacking only the anterior apex. Only the posterior half
of the right maxilla is preserved. The maxillae are transversely
compressed for the main part of their length but become wider
approaching the frontal. Anteriorly, the lateral borders of the
maxillae converge toward the long axis of the skull (TextFig. 4B); in fact, the transverse diameter of maxillae is 140 mm
at the anterior end of the rostrum (as inferred by duplicating
the distance between the lateral border of the left maxilla and
the longitudinal axis) and an increment of 10 mm is observed
200 mm posteriorly to the apex. The width of the rostrum
increases to 220 mm at 400 mm behind the apex and reaches
670 mm between the lateral apices of the infraorbital processes
of maxillae at c. 560 mm behind the anterior end of the left
maxilla. In dorsal view, the rostrum appears triangular (TextFig. 4B).
In lateral view, the maxilla forms a complete arc anterior
and under the supraorbital process of the frontal (Text-figs 2,
3A). Differing from living balaenids (Balaena mysticetus and
Eubalaena), the maxillae are depressed in front of the frontal,
and the posterior three-quarters of their dorsal border are
ventrally directed. The lateroventral margins of both maxillae
form a dorsoventrally and laterally concave border running
onwards, and slightly converging towards the long axis of the
798
PALAEONTOLOGY, VOLUME 48
1 . Skull measurements of Balaenella brachyrhynus.
NMB 42001, holotype; measurements in mm.
T A B L E 2 . Periotic and tympanic measurements of Balaenella
brachyrhynus, NMB 42001, holotype; measurements in mm.
Condylobasal length
Maximum width of skull (between postorbital
processes of supraorbital processes of frontal)
Anteroposterior diameter of supraorbital process
of frontal
Laterolateral diameter of supraorbital process
of frontal
Nasal length along medial border
Maximum width of both nasals at anterior end
Maximum width of both nasals at posterior end
Maximum width of narial opening anterior
to nasal end
Length of supraoccipital
Linear length of left maxilla
Length of left maxilla along external curvature
Posterior width of left maxilla (posterior border
of infraorbital process)
Linear length of right maxilla
Length of right maxilla along external curvature
Posterior width of right maxilla (posterior border
of infraorbital process)
Maximum width of supraoccipital between
exoccipitals
Length of left premaxillary fragment
Anterior width of left premaxillary fragment
Posterior width of left premaxillary fragment
Length of anterior fragment of right premaxilla
Length of posterior fragment of right premaxilla
Width of supraoccipital at midlength
Anteroposterior diameter of temporal fossa
Laterolateral diameter of temporal fossa
Laterolateral diameter of left occipital condyle
Anteroposterior (dorsoventral) diameter of
left occipital condyle
Estimated laterolateral diameter of foramen
magnum
Estimated anteroposterior (dorsoventral)
diameter of foramen magnum
Distance between lateral border of left
occipital condyle and lateral border of exoccipital
Distance between antorbital and postorbital
processes of supraorbital process of frontal
Length of posterior process of petrosal
Width of posterior process of petrosal at midlength
Length of anterior process of petrosal
Width of anterior process of petrosal excluding
lateral projection
Width of anterior process of petrosal including
lateral projection
Anteroposterior diameter of pars cochlearis
Lateromedial diameter of pars cochlearis
(maximum protrusion of promontorium)
Length of tympanic bulla
Anterior width of tympanic bulla
Height of tympanic bulla (from convex face to
dorsal rim of tympanic medial prominence)
Height of tympanic bulla (from lateroventral
keel to dorsal rim of tympanic medial prominence)
Maximum height of tympanic cavity
Maximum length of tympanic cavity
Maximum width of tympanic cavity
TABLE
1080
800
130
550
43
25
58.5
140
310
560
560
375
750
770
345
96
25
42
28
46
26
18.5
84
60
38
62
30
63
20
460
650
23
40
330
410
330
90
c. 250
75
100
64
80
150
105
skull. The anteriormost quarter of the rostrum abruptly projects downward over the last 57 mm.
Both maxillae bear four maxillary foramina. The infraorbital
processes are very robust and triangular in dorsal view. There
is a slight depression 110 mm in length running above the
ventrolateral border of the infraorbital process that corresponds to the antorbital notch. Rare vascular sulci related to
the blood supply for the baleen are present on the ventral
surface of the maxillae.
The maxilla articulates with the frontal through a wide, flat
process that is formed by its posteromedial corner. This process superimposes on the anteromedial portion of the frontal
T E X T - F I G . 4 . Reconstruction of the Tilburg skull (NMB
42001). A, left lateral view. B, dorsal view. The scale bar
represents 200 mm. See text for explanation of labelling.
lateral to the nasals, and it is round in posterior outline. The
infraorbital process of the maxilla and the supraorbital process
of the frontal are divided by a space that widens distally. The
infraorbital plate is developed medially under the supraorbital
process of the frontal, but it is absent more laterally so that
it cannot be observed when the skull is examined in lateral
view.
BISCONTI: DIMINUTIVE PLIOCENE WHALE
The premaxillae display a strong transverse compression and a
round dorsal profile. The ventral border is broken along the
entire length of the bones. The nasal cavity is located between
the posterior portions of the premaxillae, and its anteroventral
edge is represented by an anterodorsally ascending relief of the
medial wall of the premaxillae.
The nasal bones display a very characteristic morphology
observed in no other living and fossil balaenid (Text-fig. 4).
They are very short and their lateral borders converge anteriorly,
forming a triangular complex slightly raised relative to the maxillae. The anterior edges of the nasals are transversely and dorsoventrally round, lacking the typical notch of the other
balaenids. Posteriorly, the nasals are divided by a triangular, forward-growing portion of the frontal.
The rostral length (560 mm between anterior and posterior
end of maxilla) approaches 50 per cent of the condylobasal
length (1080 mm). This situation is observed in newborn living
balaenid species, but the holotype of Balaenella brachyrhynus is
not a juvenile individual because all of the sutures of the skull
are fused. Balaenella brachyrhynus shares two features with juveniles and newborns of living balaenids, namely the horizontal
development of the supraoccipital (see above) and the ratio of
rostral length to total skull length.
Frontal. The frontal includes two supraorbital processes and a
small interorbital region (Text-figs 2–3, 5). The right supraorbital process is broken at 410 mm from the sagittal axis of the
skull but the left one is complete. The supraorbital processes are
developed along an oblique plane descending from the higher
interorbital portion. They strongly project rearward and outward; the ventral angle between them is largely obtuse,
approaching 170 degrees. The dorsal surface of the supraorbital
process is distally flat, but medially displays a slight temporal
ascending crest that makes the dorsomedial portion of the bone
prismatic and more robust.
The antorbital process is more robust and higher than the
postorbital process. The sulcus for the optic nerve is shallow and
narrow, and it develops on the posteroventral surface of the
supraorbital process. The frontal is exposed dorsally and forms a
short interorbital region, which is 32 mm in length. The anterior
process of the supraoccipital is superimposed on the dorsal surface of the posterior portion of the interorbital region of the
frontal. The frontal is anteriorly divided by an unfused sutura
interfrontalis, and posteriorly bounded by the coronal suture
between frontals and the parietals.
Temporal fossa: parietal, squamosal. The coronal suture is evident in lateral view but not in dorsal view owing to the superimposition of the anterior process of the supraoccipital on the
parietal and the frontal. In lateral view, the squamosal suture (of
parietal and squamosal) begins from the lambdoidal suture (of
squamosal, parietal and supraoccipital) and develops ventrally.
The lambdoidal suture is marked by a robust lateral tubercle
protruding from the posterior temporal crest.
Anteriorly, the parietal is superimposed upon the lateral and
medial portions of the frontal covering the posterodorsal region
of emergence of the supraorbital processes. Presumably, the
supraoccipital superimposes on the parietal. The dorsal border
799
A
B
T E X T - F I G . 5 . A, nasal bones of the holotype skull (NMB
42001) as preserved. B, vertex structure of Balaenella
brachyrhynus. Scale bars represents 85 mm. See text for
explanation of labelling.
of the parietal forms the temporal crest overhanging the temporal fossa (i.e. the lateral walls of the skull behind the supraorbital processes of the frontal are not seen in dorsal view); the
temporal crests follow the dorsal borders of the supraoccipital
and converge anteriorly towards the sagittal line.
The squamosal is developed along the dorsoventral axis. It
projects downward and posteriorly, but it is less posteriorly orientated than the supraorbital process of the frontal. The squamosal forms the posterior wall of the temporal fossa, which is
strongly concave in this skull. This wall is laterally bound by an
undulating lateral squamosal crest (lsc). The lsc originates dorsally from the lambdoidal crest and projects forward; then it
continues ventrally generating a convex curve (anterior convexity); finally, the crest projects downward and posteriorly. The
lateral surface of the squamosal is flat. The posterodorsal profile
of the bone is rounded. Both the zygomatic and the postglenoid
processes are missing; thus, the morphology of the craniomandibular joint is unknown.
The tubercle located on the lambdoidal suture and the convex curve on the lsc limit the space occupied by the lambdoidal crest. That crest is very round, differing from the anterior
800
PALAEONTOLOGY, VOLUME 48
temporal crest and the ventrolateral lsc; in fact, it is not a true
crest but only a round convexity of the dorsal borders of the
squamosal. The lambdoidal crest represents the connection
between the temporal crest and the lsc, and its posterior apex
is behind the level of the lsc but anterior to the occipital
condyles.
Occipital region: supraoccipital and exoccipital. The supraoccipital is large and wide (Text-fig. 4B); it does not display a dome
(like Eubalaena), and its anterior end is slightly raised. The lateral borders are posteriorly convex, but lateral to the anterior
process they are concave (i.e. the anterior process of the supraoccipital is laterally compressed). The anterior process is small
and narrow, and its rostral border is linear. The anterior process
is more advanced than the supraorbital processes of the frontal
(i.e. in dorsal view, the anterior process ends more anteriorly
than the antorbital corner of the frontal).
A wide area of low relief developed along the sagittal axis of
the supraoccipital divides two anterior nuchal fossae. The main
portion of the supraoccipital is almost horizontal but the posterior part, including the foramen magnum and exoccipitals, is
more vertical.
The exoccipitals are laterally round; in dorsal view they are
slightly posterior to the deduced position of the foramen magnum. The descending processes of the basioccipital are wide and
triangular, but their ventral corners are badly eroded. Posteriorly
they are transversely orientated, but anteriorly they parallel the
longitudinal axis of the skull. The vomer divides them on the
ventral surface of the skull. The occipital condyles are wide and
form the ventrolateral sides of the foramen magnum; ventrally,
they are largely separated by a deep notch. A condylar neck is
lacking. The foramen magnum is destroyed.
Basicranial observations: pterygoid, petrosal, tympanic. As currently displayed for exhibition in the Natuurmuseum Brabant,
A
the holotype skull is on a mobile box and leans on a gypsum
pedestal so that its basicranium is largely inaccessible. Thus, it is
possible to report only significant observations of those portions
of the skull that are free of gypsum (Text-figs 6–7).
The vomer is observed in the posterior portion of the skull
where it divides the descending processes of the basioccipital.
There, it is flat and covers the suture between basisphenoid and
basioccipital, reaching a point very close to the posterior end of
the skull. The vomer is also observed in the rostrum where it is
found between the maxillae. There, it displays a strong ventral
convexity.
The palatines are not visible. The presence of the alisphenoid
in the ventral side of the temporal fossa is uncertain, as it is difficult to observe the sutural morphology owing to the gypsum
pedestal.
The pterygoids are developed along the dorsoventral axis, and
they are damaged along the posteroventral border. They display
both the medial and the lateral lamina, and a deep pterygoid
fossa. The fossa is a concavity entering the pterygoid so that it is
ventrally bordered by a pterygoid ventral lamina. The lateral
diameter of the pterygoid decreases along the dorsoventral axis.
The pterygoid is laterally bordered by the falciform process of
the squamosal, which does not display a complete infundibulum
for the external opening of the foramen pseudovale.
Only the ventral surface of the petrosal is discussed here
because the bone is articulated with the skull and its dissection
for a detailed description would be too invasive for the general
preservation of the entire skull (Text-fig. 6). Measurements of
petrosal and tympanic bullae are given in Table 2. The posterior
process of the left petrosal is articulated between exoccipital and
squamosal and emerges in the posterolateral corner of the skull.
The posterior process is long and narrow (the lateral diameter of
the pars cochlearis is c. 27 per cent of the length of the posterior
process); its ventral surface is flat, and there is no sulcus or
depression for the posterior exit of the facial nerve (VII).
B
T E X T - F I G . 6 . Periotic of Balaenella brachyrhynus holotype (NMB 42001). A, periotic as preserved in the skull. B, interpretative
drawing of periotic structures. Scale bar represents 50 mm. See text for explanation of labelling.
BISCONTI: DIMINUTIVE PLIOCENE WHALE
A
TEXT-FIG. 7.
801
B
Left tympanic bulla of the holotype skull NMB 42001. A, medial view. B, ventrolateral view. Scale bar represents 60
mm.
Approximately 57 mm anterior to the posterior end of the posterior process, a long and presumably low stylomastoid fossa
begins to develop onward; its posterior border is a depression
on the medial side of the posterior process. The posterior process forms a right angle with the anterior process. The latter is
squared and short (the lateral diameter of the pars cochlearis is
c. 61 per cent of the length of the anterior process). A triangular
process 18 mm in length projects from the posterior side of the
anterior process at an acute angle. The pars cochlearis is broadly
round and does not protrude in a cranial direction. It was
impossible to observe the cranial foramina of the pars cochlearis.
The oval window is wide and approximately elliptical; the
groove for the facial nerve is short.
Only the left tympanic bulla is preserved (Text-fig. 7). Its lateral wall is destroyed, including the sigmoid process, but the
conical process is preserved. The tympanic thickness is very
heavy; there is a high thickening along the posterior two-thirds
of the bulla, but the anterior third is narrower. The posterior
tympanic thickening is bisected by a transverse pair of sulci
developed only along the dorsal surface. The peduncles for the
articulation with the petrosal are broken; the posterior peduncle
is close to the posteromedial corner of the bulla and developed
along the anteroposterior axis. The tympanic cavity is relatively
shallow and extends behind the tympanic thickening. The ventromedial keel is pronounced but eroded; the ventral side of the
bulla is strongly concave.
COMPARISONS
Synapomorphic features
Balaenella brachyrhynus has Balaena-like characteristics in
the rostrum, in the sutural pattern of the neurocranial
bones and in the temporal fossa. The most striking feature shared by Balaenella and Balaena is the lateral process of the maxilla located under the supraorbital process
of the frontal (skull in lateral view). The supraorbital process is orientated posteriorly in Balenella brachyrhynus,
Balaena montalionis, B. mysticetus and Morenocetus parvus. In Eubalaena (including E. belgica), Balaenula astensis
and B. balaenopsis the lateral process of the maxilla and
the anterior portion of the rostrum form a right angle
(skull in lateral view).
As in Balaena mysticetus and B. montalionis, in the
Tilburg skull the supraorbital process of the frontal is distally flat; this feature is also shared with the fragment of
the frontal of the type material of Balaenotus insignis as
figured by Van Beneden (1878, pl. 27; IRSN Ct.M. 836a).
In Eubalaena, Balaenula astensis and Balaenula balaenopsis
the supraorbital process is prismatic because the ascending temporal crest is developed along its whole dorsal
surface forming a sharp edge.
Balaena mysticetus and B. ricei have a supraoccipital
with a wide and round anterior border (which is narrower
than that of Balaenula, Eubalaena and Morenocetus),
whereas in Balaenella brachyrhynus and Balaena montalionis the anterior portion of the supraoccipital is transversely compressed and the anterior border of the
supraoccipital is transversely straight.
The arrangement of the nuchal fossae of the Tilburg
skull is similar to that observed in Balaenula astensis in
which a pair of anterior fossae are displayed as slight
depressions on the dorsal surface of the supraoccipital.
There is no anterior dome followed by two serial couples
of nuchal fossae as in Eubalaena. Balaena ricei has a laterally sloping median ridge, which is not observed in any
other balaenid taxon. In the same region, Balaenula astensis and the Japanese Balaenula sp. display a median convexity that is absent in the Tilburg skull.
Resembling Balaenula astensis, the supraoccipital of
Balaenella brachyrhynus is developed along two planes:
the first plane is approximately vertical and comprises the
foramen magnum and the exoccipitals; the second is
approximately horizontal, and comprises that surface of
802
PALAEONTOLOGY, VOLUME 48
the supraoccipital which is anterior to the foramen magnum. In Balaenula balaenopsis and B. astensis the supraoccipital is obliquely bent with an obtuse angle between
the plane across the foramen magnum and exoccipitals,
and the plane of the anterior surface. The supraoccipital
is horizontal in newborns and calves of living giant balaenids (Van Beneden and Gervais 1880, 1868–79), so the
pattern observed in Balaenella brachyrhynus and Morenocetus parvus suggests that the verticality or horizontality of
the supraoccipital would depend on the size (and the age)
of the individuals. This hypothesis predicts that small
balaenid taxa have a supraoccipital developed along two
planes, and the anterior portion of the supraoccipital
should be approximately horizontal in all the small forms
independent of their phylogenetic affinities.
Balaenella brachyrhynus shares with Balaena mysticetus
and Balaenotus insignis (Ct.M. 832, 833) the flatness and
general proportions of the posterior process of the petrosal. Balaenula astensis also has a flat posterior process, but
in that species the process is markedly shortened (Bisconti
2003a). In Eubalaena glacialis the posterior process
appears different, displaying a complex, somewhat crestlike dorsal projection from the horizontal ventral portion
of the process (cfr. MSNT 264, USNM 23077). The morphology of the anterior process is shared by the Tilburg
skull, Balaena mysticetus, Eubalaena glacialis and Balaenotus insignis (Bisconti 2003a). Major differences exist
between the anterior process of Balaenella brachyrhynus
and those of Balaenula balaenopsis and B. astensis. In general, the differences between the petrosal of B. balaenopsis
and all of the other balaenids are so marked that a morphological analysis should be made to test the hypothesis
that the petrosal does not belong to a balaenid. In fact,
the petrosal of B. balaenopsis (IRSN Ct.M. 858a) was not
found in connection to the type skull (Van Beneden
1880, 1878), and it appears so different that it could easily belong to a completely different taxon, perhaps to a
cetothere (but see Bisconti 2003a). The differences are in
the morphology of the stylomastoid fossa, which is sharply defined in Balaenula balaenopsis but is not in all of
the other balaenids; in the triangular-shaped cranial opening of the facial canal, which is round in other balaenids;
and in the long and low anterior process, which is usually
short and high in the other balaenids.
The anterior process of the petrosal in Balaenula
astensis is quite delicate. Differing from the other balaenids, it is narrow, and relatively long compared with the
length of the pars cochlearis, but it is high like other
balaenids. In this respect the petrosal of Balaenula astensis is easily identifiable, being characterized by a short,
wide posterior process, and a long, transversely compressed anterior process. In both those features, the petrosal of Balaenula astensis differs consistently from
Balaenella brachyrhynus.
Autapomorphic features
The most striking autapomorphy of the Tilburg skull is
the strong reduction of the nasal bones. The nasals are
extremely short and their morphology is completely
divergent from that of the other balaenid whales. In
Balaenula astensis, B. balaenopsis and Balaena mysticetus,
the nasals are rectangular, their long axis being parallel to
the longitudinal axis of the skull; in Balaena montalionis
and Eubalaena glacialis the nasals are also rectangular but
their long axis is transverse to the longitudinal axis of the
skull. Moreover, the nasals of all balaenids but Balaenella
brachyrhynus display a notch in their anterior wall that is
also observed in dorsal view. The nasals of the Tilburg
skull are delicate and lack the notch. They form a triangular complex that interdigitates with the frontal.
The ratios between the length of the nasals (along their
medial border) and the condylobasal length of skulls
belonging to several fossil and living Balaenidae are as follows: Balaenella brachyrhynus: 2Æ77; Balaenula astensis:
10Æ71 (data determined by Bisconti 2000); B. balaenopsis:
8Æ71 (estimated from Van Beneden 1878); Eubalaena glacialis: 8Æ6, 7Æ3, 6Æ8 (mean, 7Æ56; data from Tomilin 1967);
Balaena mysticetus: 8Æ9, 8Æ91 (Tomilin 1967; Van Beneden
and Gervais 1868–79); B. montalionis: 7Æ42 (total length
of the reconstructed skull estimated as 2Æ2 m; nasal bone
length from Bisconti 2000).
The nasals of the Tilburg skull are about 60 per cent
shorter than those of the giant balaenids Balaena and
Eubalaena, and about 75 per cent shorter than those of
Balaenula astensis. This suggests that Balaenella brachyrhynus approaches the most advanced stage of nasal reduction in balaenids and possibly in the entire Mysticeti.
The Tilburg skull bears autapomorphies related to the
feeding apparatus. In particular, the robustness of the
posterolateral portion of the maxilla is remarkable. It is
possible that the strong infraorbital process of the maxilla
is related to the feeding behaviour, but the lack of a complete dentary and postcranial bones prevent a clear interpretation of function in that taxon.
PHYLOGENETIC ANALYSIS
Introduction and discussion of previous work
The phylogenetic relationships of Balaenella brachyrhynus
were investigated through a cladistic analysis of living and
extinct members of the family Balaenidae using an extended outgroup formed by representatives of the main mysticete radiations. Previous studies on Balaenidae failed in
providing a clear picture of the phylogenetic history of
these whales. McLeod et al. (1993), for instance, did not
include fossil taxa in their analysis and this prevented an
BISCONTI: DIMINUTIVE PLIOCENE WHALE
unambiguous interpretation of the evolutionary radiations
of the family. A cladistic study of Balaenidae was made
by Bisconti (2000), who included fossil taxa in the
ingroup. He discovered a clade of small balaenids comprising Balaenula astensis, B. balaenopsis and the primitive
Morenocetus parvus based on the shared features listed in
Table 3. A reinterpretation of these features (presented in
the right-hand column of Table 3) shows that only three
characters proposed by Bisconti (2000) are useful in
supporting a Morenocetus + Balaenula clade, namely: flat
posterior wall of temporal fossa (shared by Balaenula
astensis and B. balaenopsis); supraoccipital bending less
than 60 degrees (shared by all the small balaenids plus
Caperea marginata); convex lateral supraoccipital borders
(shared by B. astensis, B. balaenopsis and Morenocetus
803
parvus). The length ⁄ width ratio of the nasal bones could
be considered as another supporting character for the
Morenocetus + Balaenula clade because it is similar in
Balaenula astensis and B. balaenopsis, but unfortunately
the nasals are not preserved in Morenocetus parvus, Eubalaena belgica and Balaena ricei so that ambiguity persists.
The petrosal does not provide supporting evidence for
this clade because of the peculiar morphology of that
bone in Balaenula balaenopsis. Moreover, the petrosal of
Balaenula astensis is particularly difficult to interpret, the
posterior process being very short and the anterior process long. In general terms, the character states used by
Bisconti (2000) need to be updated with further morphological work (see Table 3 and Bisconti 2003a for a discussion of Bisconti’s 2000 dataset).
Discussion of potential synapomorphic characters proposed by Bisconti (2000) to support a clade including Balaenula
astensis, B. balaenopsis and Morenocetus parvus.
TABLE 3.
Character
Discussion
Linear mandibular rami
Seems a primitive feature for mysticetes in general; many cetotheres and Pliocene
rorquals share this character with small balaenids.
This state can be demonstrated in Balaenula astensis only; the poor preservation of
Balaenula balaenopsis prevents observation of its status; the Japanese Balaenula sp.
has a wide temporal fossa.
By ’parasagittal crest’, Bisconti (2000) meant the anterior part of the lambdoidal crest; the
state can be demonstrated for Balaenula astensis and Morenocetus parvus only; the
Japanese Balaenula sp. has high crests while it is impossible to observe the feature in
Balaenula balaenopsis.
Character shared by Balaenula astensis, Balaenula balaenopsis and Morenocetus parvus.
This feature is an autapomorphy of Balaenula astensis, its presence is doubtful in Balaenula
balaenopsis and is impossible to demonstrate in Morenocetus parvus. In the Japanese
Balaenula sp. the squamosal crest is strongly convex as in giant balaenids and the Tilburg
skull.
Poor preservation of the cranio-mandibular joint makes it impossible to be sure of
this condition in several taxa. The postglenoid process is not preserved in Balaenula astensis,
B. balaenopsis and M. parvus.
The feature is observed in Balaenula astensis, Morenocetus parvus and the Tilburg skull. In
the lst of these the bending is approximately 0 degrees, approaching the condition of
newborns of living species.
The feature is not observed in the Tilburg skull owing to transverse compression of the
anterior process of the supraoccipital.
The feature is observed in Balaenula astensis only. Eubalaena glacialis has two pairs of
nuchal fossae but their arrangement is different from Balaenula astensis. All of the other small
balaenids have one pair of anterior nuchal fossae.
Autapomorphy of Balaenula astensis.
Temporal fossa reduced along
anteroposterior and lateromedial
axes
Low parasagittal crest
Flat posterior wall of temporal fossa
Lateral squamosal crest slightly
convex anteriorly
Rectangular and anteriorly directed
temporal region
Supraoccipital bending
< 60 degrees relative to the
horizontal axis
Lateral borders of supraoccipital
convex
Two longitudinal pairs of nuchal
fossae
Vertical paroccipital process
with posterior concavity
Tuberosity absent from the posterior
surface of the paroccipital process
Lateral diameter of foramen
magnum wide with respect to the
width of the skull at the level of
exoccipitals
Ventral angle between the frontal
wings about 90 degrees
Difficult to assess without studying individual variation. However, it might be an
autapomorphy of Balaenula astensis.
Possible autapomorphy of Balaenula astensis.
The ‘frontal wings’ correspond to the supraorbital processes of the frontal. The character is
shared by Balaenula astensis and Morenocetus parvus. Poor preservation does not
permit observation of this feature in Balaenula balaenopsis and the Japanese Balaenula
804
PALAEONTOLOGY, VOLUME 48
Apart from the failure of previous morphological studies in depicting a clear interpretation of the phylogeny of
Balaenidae, molecular studies have complicated the situation further in that they have found very few genetic differences between the living genera. This led Árnason and
Gullberg (1994) to propose that living balaenids all
belong to the same genus, i.e. Balaena. This conclusion
was also shared by Gatesy (1998) but is in conflict with
the traditional morphological view in which Balaenidae
includes two living genera (Mead and Brownell 1993).
Westgate and Whitmore (2002) hypothesized that Balaena
included at least five species during the Pliocene and this
implicitly suggests that the genetic differences found in
the living taxa may not completely represent their phylogenetic history. This problem is investigated and resolved
through the cladistic analysis of living and fossil Balaenidae reported here.
Material and methods
Eighty-one morphological characters were scored for 19
taxa including 10 balaenids in the ingroup, and seven
non-balaenid mysticetes plus two archaeocete cetaceans in
the outgroup. An annotated character list and the character · taxon matrix used in the cladistic analysis are presented in the Appendix (sections 1 and 2, respectively).
The ingroup included the following taxa: Balaena montalionis, B. mysticetus, B. ricei, Eubalaena belgica, E. glacialis,
Balaenula astensis, B. balaenopsis, the Japanese B. sp.,
Balaenella brachyrhynus and Morenocetus parvus. Poorly
known taxa, such as Balaenotus insignis, ‘Balaena’ etrusca
and ‘Balaena primigenius’ were excluded from the analysis
because they are largely incomplete (Bisconti 2003a).
However, despite the exclusion of these fragmentary taxa,
the analysis represents the most inclusive phylogenetic
study of the family Balaenidae that has been attempted
hitherto. The balaenid taxa included in the cladistic analysis have been described above under comparative data
and much more extensively by McLeod et al. (1993) and
Bisconti (2003a).
In previous studies, Barnes and McLeod (1984),
McLeod et al. (1993) and Bisconti (2000) found that
the Grey whales of the family Eschrichtiidae were sister
to a clade including Neobalaenidae and Balaenidae. This
clade had been previously named Balaenoidea by Gray
(1825). Because of these studies, balaenids were suggested to be among the most derived mysticetes. A recent
morphology-based analysis of the phylogenetic relationships of the major radiations of living and fossil mysticetes (Kimura and Ozawa 2002), together with new
results from molecular studies (e.g. Árnason and Ledje
1992; Árnason and Gullberg 1994; Gatesy 1998), suggested that the Eschrichtiidae and Neobalaenidae are more
closely related to the Balaenopteridae than the Balaenidae.
These results conflicted with those of previous analyses in
also suggesting that the divergence of Balaenidae was a
basal event in the evolution of baleen-bearing mysticetes.
Given this uncertainty about the phylogenetic position of
balaenids among the mysticetes, an obvious outgroup to
this family with which to root the cladograms was not
available. Therefore, the outgroup was arranged in such a
way that the major radiations of non-balaenid mysticetes
were included. The following taxa were included within
the outgroup: the ‘cetothere’ Parietobalaena palmeri from
the Lower Miocene of the Calvert Formation of Maryland
(‘cetotheres’ are extinct rorqual-like mysticetes; there is no
general agreement about the systematics of this group; in
fact some authors have claimed that they are para- or polyphyletic whereas others have supported their monophyly:
for further information, see McLeod et al. 1993; Fordyce
and Barnes 1994; Fordyce and De Muizon 1999; Sanders
and Barnes 2002a, b), the Grey whale Eschrichtius robustus
(Eschrichtiidae), the Pygmy Right whale Caperea marginata (Neobalaenidae), the Humpback whale Megaptera novaeangliae (Balaenopteridae, Megapterinae), and the Fin
whale Balaenoptera physalus (Balaenopteridae, Balaenopterinae). Toothed mysticetes were represented by the aetiocetid Aetiocetus polydentatus from the Upper Oligocene
of Kyushu Island (Japan). The phylogenetic analysis used
two archaeocete taxa as the most external outgroups: the
middle Eocene Protocetus atavus and the early Middle–Late
Eocene Zygorhiza kochii. A list of non-balaenid specimens
examined in this work is provided in Table 4, together
with their repositories and the references used to
supplement my personal observations.
Character states were treated as unordered and
unweighted by PAUP 4.0b10 (Swofford 2002) under the
ACCTRAN character state optimization. The search for
the most parsimonious cladograms was made by treebisection-reconnection (TBR) with ten replicates and one
tree held at each step during stepwise addition followed
by bootstrap analysis with 100 replicates. A randomization test was performed by PAUP to assess the distance
of the results from 10,000 cladograms sampled equiprobably from the set of all possible trees generated from the
original matrix. Character evolution and morphological
support at nodes were assessed by the evaluation functions of Hennig86 (Farris 1988; Lipscomb 1988).
Results
General patterns. The TBR algorithm found six equally
parsimonious trees, which were 143 steps long. Their
strict-consensus is shown in Text-figure 8A together with
the bootstrap tree that had the same length (TextFig. 8B). Tree statistics are provided in the caption of
BISCONTI: DIMINUTIVE PLIOCENE WHALE
TABLE 4.
805
List of non-balaenid cetaceans examined and references of morphological descriptions.
Taxon
Repository
No.
References
Protocetus atavus
Zygorhiza kochii
Aetiocetus polydentatus
Parietobalaena palmeri
SMNS
USNM
11084 (holotype)
4748, 16638, 449538
USNM
Eschrichtius robustus
USNM
Balaenoptera physalus
NMB
ZML
MSNT
10677, 10909, 16570,
24883
364969, 364580,
364973, 364970, 364977,
504305, 571931
42002
St 13130, St 20350, 630
251, 252, 253, 258, 255,
257 (newborn)
14927 (1–2), 14935 (1–2),
14947, 14950 (1-2), 23353
263
Fraas (1904); Kellogg (1936); Luo and Gingerich (1999)
Kellogg (1936); Uhen (1998)
Barnes et al. (1994)
Kellogg (1925, 1968b)
ZMA
Megaptera novaeangliae
MSNT
USNM
ZMA
Caperea marginata
IRSN
269982, 486175 (1–2),
13656 ⁄ 16252, 21492
14952 (1–2), 14953 (1–2),
14964, 14965, 14966, 14967
1536
Text-figure 8. The randomization test (Text-fig. 9) suggested that the results of the analyses were significantly different from chance and confirmed the existence of a
phylogenetic structure in the data.
The analyses found a monophyletic suborder Mysticeti
(bootstrap support of 100 per cent) in which the toothed
aetiocetid Aetiocetus polydentatus represented the most
external taxon. TBR and bootstrap analyses converged
toward the monophyly of all the baleen-bearing mysticetes
included (bootstrap support of 99 per cent). The analyses
differed in minor details of the ingroup relationships.
In both the trees, the ‘cetothere’ Parietobalaena palmeri
was monophyletic with a clade including Eschrichtiidae
and Balaenopteridae, and Neobalaenidae was sister to
Balaenidae supporting the superfamily rank taxon named
Balaenoidea by Gray (1825; Text-fig. 8A). This taxon had
been previously reaffirmed by McLeod et al. (1993) and
Bisconti (2000) on morphological grounds and by Gatesy
(1998) based on cytochrome b DNA sequence analysis. The
Balaenoidea received a bootstrap support of 99 per cent.
Ingroup relationships. The six equally parsimonious
cladograms found by TBR and presented as strictconsensus tree in Text-figure 8A represented the most
parsimonious solutions found in this work. Their strictconsensus will be considered as the optimal tree in the
next sections. In that cladogram, balaenids are subdivided into three clades: one clade is formed by Morenocetus parvus; a second includes Balaena and Balaenella;
and a third comprises Balaenula and Eubalaena. These
True (1904); Wolman (1985)
True (1904); Gambell (1985); Bisconti (2001)
Van Beneden and Gervais (1868–79); True (1904);
Winn and Reichley (1985); Clapham and Mead (1999)
Beddard (1901); Baker (1985).
clades branched from an unsolved polytomy (Textfig. 8A). In the bootstrap tree the polytomy was solved
because Morenocetus parvus was attached to the clade
formed by Balaena and Balaenella (Text-fig. 8B). The
monophyly of the family Balaenidae received a bootstrap support of 100 per cent.
The monophyly of Eubalaena (including E. glacialis
and E. belgica) was confirmed in both the trees receiving
a bootstrap support of 84 per cent. Balaenula (including
B. astensis, B. balaenopsis and the Japanese B. sp.) was
monophyletic and received a bootstrap support value of
94 per cent with its three species branching from an
unsolved polytomy. The monophyly of Eubalaena +
Balaenula was supported by a bootstrap value of 70 per
cent.
Both the analyses converged toward a monophyletic
Balaena (bootstrap ¼ 67%) that included B. montalionis,
B. mysticetus and B. ricei. In the TBR strict-consensus tree
and in the bootstrap tree Balaena montalionis was sister
to a clade including B. mysticetus + B. ricei (supported by
a bootstrap value of 55%).
In all the cladograms, Balaenella brachyrhynus was sister
to Balaena. This sister group relationship received a bootstrap support of 89 per cent. In the bootstrap tree, Morenocetus parvus was sister to a clade including Balaenella
and Balaena; the corresponding bootstrap support value
was 65 per cent.
Character support at nodes. The character states were
mapped onto the strict-consensus TBR tree (Text-
806
PALAEONTOLOGY, VOLUME 48
Protocetus atavus
Zygorhiza kochii
Aetiocetus polydentatus
Parietobalaena palmeri
Eschrichtius robustus
Megaptera novaeangliae
Balaenoptera physalus
Caperea marginata
Morenocetus parvus
Balaenella brachyrhynus
Balaena montalionis
Balaena ricei
Balaena mysticetus
Balaenula astensis
Balaenula balaenopsis
Balaenula sp.
Eubalaena glacialis
Eubalaena belgica
Mysticeti
baleen-bearing
Mysticeti
Balaenoidea
Balaenidae
A
52
100
70
100
100
Mysticeti
baleen-bearing
Mysticeti
65
99
89
67
55
100
Balaenoidea
94
Balaenidae
B
70
84
Protocetus atavus
Zygorhiza kochii
Aetiocetus polydentatus
Parietobalaena palmeri
Eschrichtius robustus
Megaptera novaeangliae
Balaenoptera physalus
Caperea marginata
Morenocetus parvus
Balaenella brachyrhynus
Balaena montalionis
Balaena ricei
Balaena mysticetus
Balaenula astensis
Balaenula balaenopsis
Balaenula sp.
Eubalaena glacialis
Eubalaena belgica
T E X T - F I G . 8 . Phylogenetic analysis of the Balaenidae showing
the relationships of Balaenella brachyrhynus. A, strict-consensus
of six equally parsimonious trees found by tree-bisectionreconnection (TBR). B, bootstrap tree based on TBR results;
bootstrap values are located above the branches. Tree statistics
are the same for both trees: tree length, 143; consistency index
(CI), 0.7552; homoplasy index (HI), 0.2448; CI excluding
uninformative characters, 0.7518; HI excluding uninformative
characters, 0.2482; retention index (RI), 0.8818; rescaled
consistency index (RC), 0.6659.
Fig. 8A) by the DOS Equis function of Hennig86, which
also provided the reconstructions of ancestral character
states at nodes (Lipscomb 1988). In this way, it was possible to study patterns of character evolution in different
clades.
Characters 1–3 support the monophyly of the order
Cetacea (see Appendix for a character list); they have
been extensively treated by other authors (Van Beneden
1886; Fraser and Purves 1960; Kellogg 1965, 1968a; Fordyce and Barnes 1994; Luo and Gingerich 1999; Bisconti
2001, 2003a) and are not discussed again here. Of course,
the monophyly of the Cetacea is supported by more than
four morphological characters (e.g. Messenger and McGuire 1998; Luo and Gingerich 1999; O’Leary and Geisler
1999) but a discussion on cetacean monophyly is outside
the scope of the present paper.
The monophyly of the suborder Mysticeti is supported
by the following characters: 5(0 fi 1), 6(0 fi 1),
7(0 fi 1), 8(0 fi 1), 12(0 fi 1), 22(0 fi 1) 44(0 fi 1)
and 47(0 fi 1). These characters are related to the development of a wide and flat rostrum, lack of the mandibular symphysis, development of an anterior groove for
the mental ligament, presence of a complex structure (the
infundibulum; see Fraser and Purves 1960) surrounding
the foramen ‘pseudo-ovale’, uniquely derived shape of the
tympanic membrane (which is shaped as a glove finger;
Fraser and Purves 1960), and development of monophiodonty (which is also shared with odontocetes). Characters 9, 10, 21, 25, 54 and 60 are ambiguously
reconstructed and cannot be confidently used to support
the monophyly of Mysticeti.
The baleen-bearing mysticetes are diagnosed by the following characters: 11(0 fi 1), 13(0 fi 1), 14(0 fi 1),
15(0 fi 1), 16(0 fi 1), 18(0 fi 1), 55(0 fi 1) and
73(0 fi 1). From this analysis, baleen-bearing mysticetes
are uniquely characterized by the lack of teeth, the presence of baleen plates together with their vascular complement on the ventral surface of the maxilla, the lack of a
close articulation of dentary and squamosal, the presence
of a lateral squamosal crest functioning as an attachment
site for neck muscles, the lack of the hypoglossal foramen
(shared with odontocetes; however, the foramen is present in Balaenula astensis; see Bisconti 2000, 2003a), the
straight to slightly concave profile of the glenoid fossa of
the squamosal in lateral view (which is transformed into
a highly concave profile in Balaenopteridae), and a longer
supraorbital process of the frontal.
The clade including Parietobalaena palmeri, Eschrichtius
robustus, Balaenoptera physalus and Megaptera novaeangliae (‘cetotheres’, eschrichtiids and balaenopterids) is supported by the following characters: 27(0 ⁄ 1 fi 1),
51(0 ⁄ 1 fi 1), 53(0 ⁄ 1 fi 1) and 60(0 ⁄ 2 fi 2). Balaenopterids and eschrichtiids share four characters: 23(0 fi 1),
24(0 fi 1), 25(0 ⁄ 1 fi 1) and 26(0 fi 1). Characters
21(1), 22(1), 26(0 fi 1) and 44(1) are shared by Caperea
marginata and the clade including ‘cetotheres’, eschrichtiids and balaenopterids. These characters include the lack
of coalescence of the endocranial opening of the facial
canal into the internal acoustic meatus at adulthood, the
presence of a sagittal crest on the supraoccipital, the presence of a squamosal cleft and the presence of a flat rostrum. The coalescence of the internal acoustic meatus and
the endocranial opening of the facial canal has been described in the late ontogeny of balaenopterid whales (Bisconti 2001, 2003b); the meatus and facial canal are widely
separated during adulthood in some fossil ‘cetotheres’
such as Parietobalaena palmeri, Diorocetus hiatus and Mesocetus longirostris, and in the neobalaenid Caperea marginata. Among balaenids, a morphological formation that
looks like a sagittal crest has been described in a Pliocene
Eubalaena sp. from Tuscany (Bisconti 2002). The squamosal cleft is a suture observed within the squamosal of
BISCONTI: DIMINUTIVE PLIOCENE WHALE
807
225
200
number of cladograms
175
150
125
100
75
50
0
1
10
19
28
37
46
55
64
73
82
91
100
109
118
127
136
145
154
163
172
181
190
199
208
217
226
235
244
253
262
271
280
289
298
307
316
325
334
343
352
361
370
379
388
397
25
steps
T E X T - F I G . 9 . Randomization test. The histogram depicts the tree length distributions of 10,000 cladograms equiprobably sampled
from the set of all possible cladograms based on the character · taxon matrix presented in the Appendix. This result combined ten
separate randomization tests each of which generated 1000 random cladograms. Mean tree length, 351.8; mean standard deviation,
24.53. The arrow indicates the tree length of the most parsimonious cladograms found by TBR whose strict-consensus is presented in
Text-figure 8A.
balaenopterids, neobalaenids and some late ‘cetotheres’;
from the present analysis the presence of a squamosal
cleft should be interpreted as a convergence in different
mysticete clades. Character 44 is concerned with the orientation of the dorsolateral surface of the maxilla in mysticetes: balaenids are unique in having the anterior
portion of the maxilla characterized by a transversely
compressed and dorsoventrally depressed dorsolateral surface; in neobalaenids, the dorsolateral surface of the maxilla is horizontal and not dorsoventrally depressed as in
balaenids; however, as in balaenids, the maxilla in neobalaenids has a transversely compressed dorsolateral surface
(character 44(0 fi 1)).
The monophyly of the superfamily Balaenoidea is
supported by the following characters: 17(0 fi 1),
27(0 ⁄ 1 fi 2),
28(0 fi 1),
31(0 fi 1),
33(0 fi 1),
34(0 fi 1), 35(0 fi 1), 38(0 fi 2), 40(0 fi 2), 43(0 fi 1)
and 56(0 fi 1). These include a suite of morphological
transformations related to hearing and feeding: low and
flattened tympanic bulla with a low sygmoid process, elevated neurocranium and deep skull, well-developed rostral arch, short zygomatic process of the squamosal, low
and round angular process of the dentary, relative position of the posterolateral corner of the exoccipital and the
postglenoid process, and superimposition of the supraoccipital onto the parietal (this pattern is different from that
of Balaenopteridae, Eschrichtiidae and ‘cetotheres’ in
which the supraoccipital is developed in between the parietals). Characters 57 and 59 are reverted in the Eubalaena + Balaenula clade.
Characters 29(0 fi 1), 45(0 fi 1), 46(0 fi 1), 47(1 fi
2), 48(0 fi 1), 49(0 fi 1), 50(0 fi 1), 51(0 ⁄ 1 fi 2),
52(0 fi 1), 53(0 fi 2) and 54(1 fi 2) support the
monophyly of the family Balaenidae. Balaenids are
uniquely characterized by the possession of a wide manus,
anterior torsion in the dentary, mylohyoidal sulcus along
the ventromedial surface of the dentary, incomplete infundibulum around the foramen ‘pseudo-ovale’, location
of the pterygoid near the posterior border of the skull,
presence of a well-developed ventral lamina of the pterygoid fossa, palatines partially covering the pterygoids,
long baleen, dorsoventral orientation of the squamosal,
dorsoventrally compressed round window, long and shallow stylomastoid fossa, and long and triangular lateral
projection of the anterior process of the periotic.
Among Balaenidae, the monophyly of Balaenula is supported by characters 70(0 fi 1), 71(0 fi 1) and
72(0 fi 1); these characters have been described in the
introduction of this paper and in Bisconti (2003a). The
monophyly of Eubalaena (including here only E. glacialis
and E. belgica) is due to the sharing of characters 68
(presence of a dome on the anterior portion of the supraoccipital: 0 fi 1) and 69 (squared exoccipital in lateral
view: 0 fi 1). Balaenula and Eubalaena form a monophyletic group diagnosed by the following synapomorphies:
62 (abrupt depression of the premaxilla in the anterior
half of the rostrum: 0 fi 1), 63 (irregular profile of the
skull due to the development of a distinctive apex
between supraoccipital and frontal: 0 fi 1) and 67
(spreading of the parietal onto the supraorbital process of
808
PALAEONTOLOGY, VOLUME 48
the frontal medially). Characters 57(1 fi 0) and
59(1 fi 0) are interpreted as unique reversions in the
Balaenula + Eubalaena clade.
The monophyly of Balaena is unambiguously supported by two synapomorphies: 65 (raising of the nasals
together with the proximal rostrum: 0 fi 1) and 66
(presence of a crest-like relief on the parietal squama:
0 fi 1). Balaena mysticetus and B. ricei are more closely
related than each is with B. montalionis because of the
rounder morphology of the anterior border of the supraoccipital (60(1 fi 4)). Balaenella brachyrhynus and Balaena form a monophyletic group characterized by the
following unambiguous synapomorphies: 58(0 ⁄ 1 fi 1),
60(0 fi 1), 61(0 ⁄ 1 fi 2) and 64(0 fi 1). These characters
support the view that Balaenella and Balaena share the
posterior orientation of the lateral process of the maxilla
(which, in lateral view, seems to be located under the
supraorbital process of the frontal), distal absence of the
infraorbital plate, and glenoid fossa of the squamosal
located posterior to the posterior apex of the lambdoidal
crest. A marked transverse constriction of the anterior
portion of the supraoccipital is uniquely shared by Balaenella brachyrhynus and Balaena montalionis. Characters
57, 59 and 62 are shared by Balaenella, Balaena and Caperea marginata.
DISCUSSION
The discovery of Balaenella brachyrhynus in the Lower
Pliocene of the North Sea region helps our understanding
of the evolution of body size in balaenid whales. In particular, the phylogenetic analysis presented here suggests that
the origin of the gigantic size typical of the living Right
and Bowhead whales was attained independently in these
different clades. A small size was a common condition in
Pliocene balaenids (such as in Balaenula and Balaenella)
and in the Lower Miocene Morenocetus parvus. Pliocene
species belonging to the extant genera were also commonly
small with respect to the gigantic sizes of the living balaenids (Bisconti 2000, 2002; Westgate and Whitmore 2002).
The extinction of all the small balaenids took place possibly before the end of the Pliocene in all the oceans of the
world, erasing much of the Pliocene diversity of the family.
The reasons for this large-scale (in geographical terms)
extinction are not yet completely understood but theoretical models are beginning to emerge (Bisconti 2003a) that
deserve further investigation.
One of the most important results of the present paper
is the unambiguous definition of two main balaenid radiations: one includes Balaenella brachyrhynus plus the
genus Balaena, and the other includes the genera Eubalaena and Balaenula. The phylogenetic position of Morenocetus parvus is still uncertain, given the low bootstrap
support received by its inclusion in the first clade as sister
to Balaenella + Balaena. The phylogenetic analysis presented here conflicts with the previous results published by
Bisconti (2000) in which a clade including the genera
Morenocetus and Balaenula was discovered. As discussed
in Table 3, the synapomorphies proposed to support that
clade revealed plesiomorphic character states and are no
longer useful.
The results of the new analysis strongly support a close
relationship of Eubalaena and Balaenula, two genera well
represented in Pliocene and Pleistocene sediments of Europe, USA and Japan (see Bisconti 2000 and 2002 for
reviews of the fossil records of these genera). They show
the highest morphological distance from Caperea marginata, the sister taxon to Balaenidae. In fact, in both
genera, a complete restructuring of the skull occurred
that was characterized by the interruption of the general
curvature of the premaxilla, the transverse elongation of
the supraorbital process of the frontal, the transverse
expansion of the anterior portion of the supraoccipital,
and a higher elevation of the vertex leading to the interruption of the continuous curvature of the dorsal profile
of the skull in lateral view. In Balaenula the retention of
the primitive round anterior border of the supraoccipital
(shared with Morenocetus parvus and Caperea marginata)
was paralleled by the development of a suite of derived
character states affecting the temporal and the exoccipital
regions of the skull (see also Bisconti 2003a).
The clade including the genera Balaena and Balaenella
retained the posterior orientation of the supraorbital process of the frontal, the distal absence of the ascending
temporal crest from the supraorbital process of the frontal, and a round exoccipital as in Caperea marginata and
Morenocetus parvus, together with a regular profile of the
skull in lateral view, continuously arched rostrum, and
lateral process of the maxilla located under the frontal
in lateral view. The absence of the distal portion of the
infraorbital plate represents an apomorphic feature absent
in the other balaenid clades. Unfortunately, it is impossible to score this character for Morenocetus parvus because
the maxilla is absent.
Balaenella brachyrhynus and Balaena montalionis share
a transversely constricted anterior portion of the supraoccipital whereas a marked constriction is absent in Balaena
mysticetus and B. ricei (Westgate and Whitmore 2002).
This character is not, however, sufficient to support the
monophyly of Balaenella brachyrhynus and Balaena
montalionis to the exclusion of Balaena ricei and B. mysticetus, and this reinforces the establishment of a different
genus for the Tilburg skull.
The generic differences characterizing Balaenella brachyrhynus are observed in the nasal bones, the rostrum
and the lower inclination of the supraoccipital. While the
last character is independent of the phylogenetic position
BISCONTI: DIMINUTIVE PLIOCENE WHALE
of the Tilburg skull seemingly related to the small size of
the whale, the morphology of the nasal bones and the
rostrum strongly support a generic distinction. The maxilla of B. brachyrhynus is depressed anterior to the frontal
whereas in Balaena it is highly arched and projects dorsally, anterior to the frontal (see Bisconti 2003a). The
nasal bones of Balaenella brachyrhynus show the highest
degree of reduction observed among the whole suborder
Mysticeti; these bones are small, short and horizontal,
and differ from the corresponding bones of the other
Balaenidae, which are usually rectangular and bear a
notch on the anterior border (see images in True 1904;
Cummings 1985; see also Bisconti 2000, 2003a). The
function of the small, delicate nasals of Balaenella brachyrhynus, if any, is not yet understood.
The discovery of the Tilburg skull adds important
information on the morphological evolution of Balaenidae and documents an unsuspected diversity among the
small balaenids. Three genera are currently known that
are uniquely characterized by small species: Morenocetus,
Balaenella and Balaenula. The systematic position of the
small genus Balaenotus is not yet clear because it is too
poorly known. Future studies should provide convincing
evidence on the phylogenetic placement of the Lower
Miocene Morenocetus parvus in order to make it possible
to assess the divergence times of the living genera from
their last common ancestor. This information is crucial
for conservation biologists in order to test the estimated
rates of evolution and the genetic health of the living
balaenid populations (Rooney et al. 2001).
CONCLUSIONS
In this paper, a new genus and species of a balaenid
whale has been described and compared with all the living and fossil members of the family Balaenidae. The specimen concerned is from the Lower Pliocene near
Antwerp (Belgium) and is named Balaenella brachyrhynus.
This whale is characterized by being the smallest representative of the Balaenidae, and in having a depressed maxilla anterior to the frontal, horizontal supraoccipital,
anterior border of the supraoccipital transversely constricted, and supraorbital process of the frontal directed posteriorly. The most intriguing feature is that it shows the
highest degree of nasal reduction among the mysticetes.
The phylogenetic relationships of Balaenella brachyrhynus investigated through a cladistic analysis of an ingroup
of several balaenid and non-balaenid mysticetes resulted
in the discovery of two main balaenid radiations: one
including the genera Eubalaena and Balaenula, and the
other including Balaena and Balaenella. The phylogenetic
position of the Early Miocene Morenocetus parvus was not
confidently established but it seems more closely related
809
to the Balaena + Balaenella clade than to the Eubalaena + Balaenula clade. The analysis also confirmed the
position of Caperea marginata as sister to the family Balaenidae.
Balaenella brachyrhynus is sister to Balaena. Its morphology, together with its phylogenetic position, documents an unsuspected diversity among the small
balaenids of the Pliocene and suggests that small size has
been a common condition among the balaenids just a few
million years ago.
Acknowledgements. I am indebted to Frans Ellenbroek (director of NMB, Tilburg, Holland) who allowed me to study the
specimen, and Marie-Cecile Van De Wiel (NMB) who assisted
me during my work and provided help on several occasions. I
thank Klaas Post (Natuurmuseum Rotterdam, Holland) very
much for making it possible for me to study the Dutch collections of fossil mysticetes, providing literature, making useful
comments on an early draft of the manuscript, and kindly
assisting me during my visits to Holland. Thanks are also due
to Olivier Lambert for his help during my study of the IRSN
collection and to David Bohaska who assisted me during the
study of the USNM collection. Albert Sanders (The Charleston
Museum, Charleston, South Carolina) provided a thorough
and insightful review of the manuscript: his help is gratefully
acknowledged. Mark Uhen (Cranbrook Institute of Science,
Bloomfield Hills, Michigan) and Oliver Hampe (Museum fur
Naturkunde, Berlin, Germany) carefully reviewed the manuscript, providing suggestions that significantly improved the
quality of the paper. This work has been supported by
MURST funds, being a contribution of the Pisa Unit (Unit
coordinator Walter Landini, Dipartimento di Scienze della
Terra, University of Pisa) to the research project ‘Palaeobiogeography of Central Mediterranean from Miocene to Quaternary’ (national coordinator Danilo Torre, Dipartimento di
Scienze della Terra, University of Florence).
REFERENCES
A B E L , O. 1941. Vorläufige mitteilungen uber die Revision der
fossilen mystacoceten aus dem tertiär belgiens. Bulletin du
Musée Royal d’Histoire Naturelle Belgique, 17, 1–29.
Á R N A S O N , U. and G U L L B E R G , A. 1994. Relationship of
baleen whales established by cytochrome b gene sequence
comparison. Nature, 367, 726–728.
–––– and L E D J E , C. 1992. The use of highly repetitive DNA
for resolving cetacean and pinniped phylogenies. 74–80. In
S Z A L A Y , F. S., N O V A C E K , M. J. and M c K E N N A ,
M. C. (eds). Mammal phylogeny. Volume 2: Placentals. Springer Verlag, New York, 321 pp.
B A K E R , A. N. 1985. Pygmy right whale – Caperea marginata.
345–355. In R I D G W A Y , S. M. and H A R R I S O N , R. (eds).
Handbook of marine mammals. Volume 3: the Sirenians and
baleen whales. Academic Press, New York, 362 pp.
B A R N E S , L. G. 1977. Outline of eastern North Pacific fossil
cetacean assemblage. Systematic Zoology, 25, 321–343.
810
PALAEONTOLOGY, VOLUME 48
–––– and M c L E O D , S. A. 1984. The fossil record and phyletic
relationships of Gray Whales. 3–32. In J O N E S , M. L.,
L E A T H E R W O O D , S. and S W A R T Z , S. (eds). The Gray
Whale. Academic Press, Orlando, 600 pp.
–––– K I M U R A , M., F U R U S A W A , H. and S A W A M U R A ,
H. 1994. Classification and distribution of Oligocene Aetiocetidae (Mammalia; Cetacea; Mysticeti) from western North
America and Japan. Island Arc, 3, 392–431.
B E D D A R D , F. E. 1901. Contribution towards knowledge of
the osteology of the pigmy whale (Neobalaena marginata).
Transactions of the Zoological Society, 16, 87–108.
B E N E D E N , P.-J. van 1886. Description des ossements fossiles
des environs d’Anvers. Genres: Amphicetus, Heterocetus, Mesocetus, Idiocetus &. Isocetus. Annales du Musée Royal d’Histoire
Naturelle de Belgique, 13, 1–139 + atlas.
–––– 1880. Description des ossements fossiles des environs d’Anvers. Cétacés Genres Balaenula, Balaena et Balaenotus. Annales
du Musée Royal d’Histoire Naturelle de Belgique, 4, 1–83.
–––– 1878. Description des ossements fossiles des environs d’Anvers. Cétacés Genres Balaenula, Balaena et Balaenotus. Annales
du Musée Royal d’Histoire Naturelle de Belgique, Atlas, 4, pls
1–38.
–––– and G E R V A I S , P. 1880. Ostéographie des Cétacés vivants
et fossiles. Arthus Bertrand, Paris, 634 pp.
–––– –––– 1868–79. Osteographie des Cetaces vivants et fossiles.
Atlas, Arthus Bertrand, Paris, pls 1–64.
B E N K E , H. 1993. Investigations on the osteology and the functional morphology of the flipper of whales and dolphins (Cetacea). Investigations on Cetacea, 24, 9–252.
B E R T A , A. and S U M I C H , J. L. 1999. Marine mammals: evolutionary biology. Academic Press, London, 512 pp.
B I S C O N T I , M. 2000. New description, character analysis and
preliminary phyletic assessment of two Balaenidae skulls from
the Italian Pliocene. Palaeontographia Italica, 87, 37–66.
–––– 2001. Morphology and postnatal growth trajectory of rorqual petrosal. Italian Journal of Zoology, 68, 87–93.
–––– 2002. An early Late Pliocene Right whale (genus Eubalaena) from Tuscany (central Italy). Bollettino della Società Paleontologica Italiana, 41, 83–91.
–––– 2003a. Evolutionary history of Balaenidae. Cranium, 20,
9–50.
–––– 2003b. Systematics, paleoecology, and paleobiogeography
of archaic mysticetes from the Italian Neogene. Unpublished
PhD thesis, University of Pisa, 344 pp.
B U R N S , J. J., M O N T A G U E , J. J. and C O W L E S , C. J. (eds)
1993. The Bowhead whale. The Society for Marine Mammalogy,
Special Publication, 2, 1–787.
C A B R E R A , A. 1926. Cetáceos fósiles del Museo de La Plata.
Revista del Museo de la Plata, 29, 363–411.
C A P E L L I N I , G. 1877. Le traces de l’homme Pliocène en Toscane. Imprimerie Franklin-Tarsulat, Budapest, 12 pp.
–––– 1904. Balene fossili toscane. II. Balaena montalionis. Memorie della Regia Accademia delle Scienze dell’Istituto di Bologna,
6, 45–57.
C L A P H A M , P. J. and M E A D , J. G. 1999. Megaptera novaeangliae. Mammalian Species, 604, 1–9.
C U M M I N G S , W. C. 1985. Right Whales Eubalaena glacialis
(Müller, 1776) and Eubalaena australis (Desmoulins, 1822).
275–304. In R I D G W A Y , S. H. and H A R R I S O N , R.
(eds). Handbook of Marine Mammals. Volume 3: The sirenians and baleen whales. Academic Press, New York, 362
pp.
C U V I E R , G. 1823. Recherches sur les ossemens fossiles, où l’on
rètablit les caractères de plusieurs animaux dont les révolutions
du globe ont détruit les espéces, 5, 309–398.
EXCAVATION RESEARCH GROUP FOR THE FUKAG A W A W H A L E F O S S I L 1982. Research report on the
Pliocene Balaenula (Suborder Mysticoceti) collected from
Fukagawa City, Hokkaido, 131 pp.
F A R R I S , J. 1988. Hennig86. Reference manual. Distributed by
the author, 15 pp.
F O R D Y C E , R. E. and B A R N E S , L. G. 1994. The evolutionary
history of whales and dolphins. Annual Review of Earth and
Planetary Sciences, 22, 419–455.
–––– and D E M U I Z O N , C. 1999. Evolutionary history of cetaceans: a review. 169–233. In M A Z I N , J.-M. and D E B U F F R E N I L , V. (eds). Secondary adaptations of tetrapods to life
in water. Verlag Pfeil, München, 367 pp.
F R A A S , E. 1904. Neue Zeuglodonten aus dem Unteren Mitteleocän vom Mokattam bei Cairo. Geologische und Palaeontologische Abhandlungen, 6, 199–220.
F R A S E R , F. C. and P U R V E S , P. E. 1960. Hearing in cetaceans. Bulletin of the British Museum (Natural History), Zoology, 7, 1–140.
G A M B E L L , R. 1985. Fin whale – Balaenoptera physalus. 171–
192. In R I D G W A Y , S. M. and H A R R I S O N , R. (eds).
Handbook of Marine Mammals. Volume 3: the sirenians and
baleen whales. Academic Press, New York, 362 pp.
G A T E S Y , J. 1998. Molecular evidence for the phylogenetic
affinities of Cetacea. 63–112. In T H E W I S S E N , J. G. M.
(ed.). The emergence of whales. Evolutionary patterns in the origin of Cetacea. Plenum Press, New York, 477 pp.
G E I S L E R , J. H. and L U O , Z. 1996. The petrosal and inner ear
of Herpetocetus sp. (Mammalia: Cetacea) and their implications for the phylogeny and hearing of archaic mysticetes.
Journal of Paleontology, 70, 1045–1066.
–––– –––– 1998. Relationships of Cetacea to terrestrial ungulates
and the evolution of cranial vasculature in Cete. 163–212. In
T H E W I S S E N , J. G. M. (ed.). The emergence of whales. Evolutionary patterns in the origin of Cetacea. Plenum Press, New
York, 477 pp.
G R A Y , J. E. 1825. Outline of an attempt at the disposition of
the Mammalia into tribes and families with a list of the genera
apparently appertaining to each tribe. Philosophical Annals, 26,
337–344.
H O E D E M A K E R S , K. and M A R Q U E T , R. 1992. Lithostratigraphy of Pliocene deposits in the Liefkenshoektunnel construction works near Kallo (NW Belgium). Contributions to
Tertiary and Quaternary Geology, 29, 21–25.
J A N S S E N , A. W. 1974. Het profiel van de bouwput onder het
eerste kanaaldok nabij Kallo, Provincie Oost Vlaanderen, België. Mededelingen van de Werkgroep voor Tertiaire en Kwartaire
Geologie, 11, 173–185.
K E L L O G G , R. 1925. Description of a new genus and species
of whalebone whale from the Calvert Cliffs, Maryland. Proceedings of the United States National Museum, 63, 1–14.
BISCONTI: DIMINUTIVE PLIOCENE WHALE
–––– 1934. A new cetothere from the Modelo Formation at Los
Angeles, California. Contributions to Palaeontology, Carnegie
Institution, Washington, 447, 85–104.
–––– 1936. A review of the Archaeoceti. Contributions to Palaeontology, Carnegie Institution of Washington, 482, 1–366.
–––– 1965. Fossil marine mammals from the Miocene Calvert
Formation of Maryland and Virginia. United States National
Museum, Bulletin, 247, 1–63.
–––– 1968a. Fossil marine mammals from the Miocene Calvert
Formation of Maryland and Virginia. United States National
Museum, Bulletin, 247, 103–197.
–––– 1968b. Supplement to description of Parietobalaena palmeri. 175–197. In K E L L O G G , R. (ed.). Fossil marine mammals from the Miocene Calvert Formation of Maryland and
Virginia. United States National Museum, Bulletin, 247, 103–
197.
–––– 1968c. Miocene Calvert mysticetes described by Cope. 103–
132. In K E L L O G G , R. (ed.). Fossil marine mammals from
the Miocene Calvert Formation of Maryland and Virginia. United States National Museum, Bulletin, 247, 103–197.
K I M U R A , T. and O Z A W A , T. 2002. A new cetothere (Cetacea: Mysticeti) from the Early Miocene of Japan. Journal of
Vertebrate Paleontology, 22, 684–702.
L A M B E R T S E N , R. H., U L R I C H , N. and S T R A L E Y , J.
1995. Frontomandibular stay of Balaenopteridae: a mechanism
for momentum recapture during feeding. Journal of Mammalogy, 76, 877–899.
L I P S C O M B , D. 1988. Cladistic analysis using Hennig86. George
Washington University, Washington DC, 122 pp.
L U O , Z. 1998. Homology and transformation of cetacean ectotympanic structures. 269–302. In T H E W I S S E N , J. G. M.
(ed.). The emergence of whales. Evolutionary patterns in the origin of Cetacea. Plenum Press, New York, 477 pp.
–––– and G I N G E R I C H , P. D. 1999. Terrestrial Mesonychia to
aquatic Cetacea: transformation of the basicranium and evolution of hearing in whales. University of Michigan, Papers in
Paleontology, 31, 1–98.
M A L I K , S., B R O W N , M. W., K R A U S , S. D. and W H I T E ,
B. N. 2000. Analysis of mitochondrial DNA diversity within
and between North and South Atlantic Right whales. Marine
Mammal Science, 16, 545–559.
M c L E O D , S. A., W H I T M O R E , F. C. Jr and B A R N E S , L.
G. 1993. Evolutionary relationships and classification. 45–70.
In B U R N S , J. J., M O N T A G U E , J. J. and C O W L E S , C. J.
(eds). The Bowhead whale. The Society for Marine Mammalogy, Special Publication, 2, 1–787.
M E A D , J. G. and B R O W N E L L , R. L. Jr 1993. Order Cetacea.
349–364. In W I L S O N , D. E. and R E E D E R , D. M. (eds).
Mammal species of the world. Smithsonian Institution Press,
Washington, 1206 pp.
M E S S E N G E R , S. and M c G U I R E , J. A. 1998. Morphology,
molecules, and the phylogenetics of Cetaceans. Systematic Biology, 47, 90–124.
M O N E G A T T I , P. and R A F F I , S. 1996. Castell’Arquato ei
suoi dintorni: la culla degli studi sul Pliocene. 43–61. In
D O M I N I C I , S., I A C C A R I N O , S., M E L I S , R.,
M O N E G A T T I , P., M O N T E N E G R O , E., M U T T I , E.,
P E L O S I O , G., P U G L I E S E , N., R A F F I , S., Z A N Z U C -
811
C H I , G. and Z A V A L A , C. (eds). XIII Convegno della Società
Paleontologica Italiana. Guida alle Escursioni. Centro Grafico
Università di Parma, Parma, 69 pp.
N I S H I W A K I , M. and H A S E G A W A , Y. 1969. The discovery
of the right whale skull in the Kisagata Shell Bed. Scientific
Reports of the Whales Research Institute, 21, 79–84.
N U Y T S , H. 1990. Note on the biostratigraphy (benthic foraminifera) and lithostratigraphy of Pliocene deposits at Kallo
(Oost-Vlaanderen; Belgium). Contributions to Tertiary and
Quaternary Geology, 27, 17–24.
O ’ L E A R Y , M. A. and G E I S L E R , J. H. 1999. The position of
Cetacea within Mammalia: phylogenetic analysis of morphological data from extinct and extant taxa. Systematic Biology, 48,
455–490.
O I S H I , M. and H A S E G A W A , Y. 1994. Diversity of
Pliocene mysticetes from eastern Japan. Island Arc, 3, 436–
452.
O K A Z A K I , Y. 1994. A new type of primitive baleen whale
(Cetacea; Mysticeti) from Kyushu, Japan. Island Arc, 3, 432–
435.
P E R R Y , S. L., D E M A S T E R , D. P. and S I L B E R , G. K. 1999.
The Right Whales. In P E R R Y , S. L., D E M A S T E R , D. P.
and S I L B E R , G. K. (eds). The great whales: history and status of six species listed as endangered under the U.S. Endangered Species Act of 1973. Marine Fishery Review, 61, 7–23.
P I L L E R I , G. 1986. Beobachtungen an den fossilen Cetaceen des
Kaukasus. Brain Anatomy Institute, Ostermundigen, Switzerland, 40 pp.
–––– 1987. The Cetacea of the Italian Pliocene with a descriptive
catalogue of the species in the Florence Museum of Paleontology.
Brain Anatomy Institute, Ostermundigen, Switzerland, 160 pp.
P L I S N I E R - L A D A M E , F. and Q U I N E T , G. E. 1969. Balaena
belgica Abel 1938, Cetace du merxemien d’Anvers. Bulletin de
l’Institut Royal du Sciences Naturelles Belgique, 45, 1–6.
P O R T I S , A. 1883. Nuovi studi sulle traccie attribuite all’uomo
pliocenico. Memorie della Regia Accademia delle Scienze di
Torino, 35, 3–27.
R E E V E S , R. R. and L E A T H E R W O O D , S. 1985. Bowhead
whale Balaena mysticetus Linnaeus, 1758. 305–343. In R I D G W A Y , S. H. and H A R R I S O N , R. (eds). Handbook of marine
mammals. Volume 3: the sirenians and baleen whales. Academic
Press, New York, 362 pp.
R I D G W A Y , S. H. and H A R R I S O N , R., (eds). 1985. Handbook of marine mammals. Volume 3: the sirenians and baleen
whales. Academic Press, New York, 362 pp.
R I O , D., S P R O V I E R I , R. and D I S T E F A N O , E. 1994. The
Gelasian Stage: a proposal of a new chronostratigraphic unit
of the Pliocene series. Rivista Italiana di Paleontologia d Stratigrafia, 100, 103–124.
R O O N E Y , A. P., H O N E Y C U T T , R. L. and D E R R , J. N.
2001. Historical population size change of Bowhead whales
inferred from DNA sequence polymorphism data. Evolution,
55, 1678–1685.
R O S E N B A U M , H. C., B R O W N E L L , R. L. Jr, B R O W N , M.
W., S C H A E F F , C., P O R T W A Y , V., W H I T E , B. N., M A L I K , S., P A S T E N E , L. A., P A T E N A U D E , N. J., B A K E R ,
C. S., R O W N T R E E , V., T Y N A N , C. T., B A N N I S T E R , J.
L. and D E S A L L E , R. 2000. World-wide genetic differenti-
812
PALAEONTOLOGY, VOLUME 48
ation of Eubalaena: questioning the number of right whale
species. Molecular Ecology, 9, 1793–1802.
S A N D E R S , A. E. and B A R N E S , L. G. 2002a. Paleontology of
the Late Oligocene Ashley and Chandler Bridge formations of
South Carolina 2: Micromysticetus rothauseni, a primitive cetotheriid mysticete (Mammalia, Cetacea). 271–293. In E M R Y ,
R. J. (ed.). Cenozoic mammals of land and sea: tributes to the
career of Clayton E. Ray. Smithsonian Contributions to Paleobiology, 93, 1–372.
–––– –––– 2002b. Paleontology of the Late Oligocene Ashley
and Chandler Bridge formations of South Carolina 3: Eomysticetidae, a new family of primitive Oligocene mysticetes
(Mammalia: Cetacea), from South Carolina, U.S.A. 313–356.
In E M R Y , R. J. (ed.). Cenozoic mammals of land and sea:
tributes to the career of Clayton E. Ray. Smithsonian Contributions to Paleobiology, 93, 1–372.
S A N D E R S O N , L. R. and W A S S E R S U G , R. 1993. Convergent and alternative designs for vertebrate suspension feeding.
37–112. In H A N K E N , J. and H A L L , B. K. (eds). The skull.
Volume 3: Functional and evolutionary mechanisms. University
Press of Chicago, Chicago, 460 pp.
S P R O V I E R I , R. 1992. Mediterranean Pliocene biochronology:
a high resolution record based on quantitative planktonic
foraminifera distribution. Rivista Italiana di Paleontologia
e Stratigrafia, 98, 61–100.
S W O F F O R D , D. L. 2002. PAUP – Phylogenetic Systematics
Using Parsimony. Beta Documentation. Laboratory of
Molecular Systematics, Smithsonian Institution. Available at
http://paup.csit.fsu.edu/.
T O M I L I N , A. G. 1967. Cetacea. 1–756. In H E P T N E R , V. G.
(ed.). Mammals of the. U.S.S.R. and adjacent countries. Israel
Program for Scientific Translations, Jerusalem, 756 pp.
T R E V I S A N , L. 1941. Una nuova specie di Balaenula pliocenica.
Palaeontographia Italica, 40, 1–13.
T R U E , F. W. 1904. The whalebone whales of the western north
Atlantic. Smithsonian Contributions to Knowledge, 33, 1–322.
U H E N , M. D. 1998. Middle to Late Eocene basilosaurines and
dorudontines. 29–63. In T H E W I S S E N , J. G. M. (ed.). The
emergence of whales. Evolutionary patterns in the origin of Cetacea. Plenum Press, New York, 477 pp.
W E S T G A T E , J. W. and W H I T M O R E , F. C. Jr 2002. Balaena
ricei, a new species of Bowhead Whale from the Yorktown
Formation (Pliocene) of Hampton, Virginia. 295–312. In
E M R Y , R. J. (ed.). Cenozoic mammals of land and sea: tributes to the career of Clayton E. Ray. Smithsonian Contributions
to Paleobiology, 93, 1–372.
W H I T M O R E , F. C. Jr 1994. Neogene climatic change and the
emergence of the modern whale fauna of the North Atlantic
ocean. 223–227. In B E R T A , A. and D E M É R É , T. A. (eds).
Contributions in marine mammal paleontology honoring Frank
C. Whitmore, Jr. Proceedings of the San Diego Society of Natural History, 29, 1–268.
W I N N , H. E. and R E I C H L E Y , N. E. 1985. Humpback whale
– Megaptera novaeangliae. 241–274. In R I D G W A Y , S. M.
and H A R R I S O N , R. (eds). Handbook of marine mammals.
Volume 3: the sirenians and baleen whales. Academic Press,
London, 362 pp.
W O L M A N , A. A. 1985. Gray whale – Eschrichtius robustus. 67–
90. In R I D G W A Y , S. M. and H A R R I S O N , R. (eds).
Handbook of marine mammals. Volume 3: the sirenians and
baleen whales. Academic Press, London, 362 pp.
Z E I G L E R , C. V., C H A N , G. L. and B A R N E S , L. G. 1997. A
new Late Miocene balaenopterid whale (Cetacea: Mysticeti),
Parabalaenoptera baulinensis, (new genus and species) from
the Santa Cruz Mudstone, Point Reyes Peninsula, California.
Proceedings of the California Academy of Sciences, 50, 115–
138.
APPENDIX
2. Air sinus: 0, absent; 1, present around the tympanic bulla
(Fraser and Purves 1960; Luo and Gingerich 1999).
3. Ascending temporal crest: 0, absent; 1, present. This crest is
located on the supraorbital process of the frontal in mysticetes; it can be located on the posterodorsal edge of the process (Oligocene toothed and baleen-bearing mysticetes), at
the middle of the process (‘cetotheres’, eschrichtiids, balaenids, and neobalaenids) or along its anterior border (balaenopterids) (Fordyce and Barnes 1994).
4. Parietal and squamosal are bulged into the temporal fossa: 0,
no; 1, yes. The bulging of the parietal and squamosal into the
temporal fossa is observed in basilosaurid archaeocetes, ‘cetotheres’, and eschrichtiids.
5. Plate-like infraorbital process of the maxilla: 0, absent; 1, present (Messenger and McGuire 1998; Sanders and Barnes
2002b).
6. Mandibular symphysis: 0, present; 1, absent (groove for mental ligament present) (Messenger and McGuire 1998; Sanders
and Barnes 2002b).
7. Tympanic membrane: 0, present; 1, modified into glove finger
(Fraser and Purves 1960; Messenger and McGuire 1998).
Morphological characters used in the phylogenetic analysis
The following is an annotated list of the character states used
in the cladistic analysis. A brief discussion of the characters is
provided only for characters described here for the first time
or not used in previous cladistic analyses of the mysticetes.
Otherwise, the characters are referred to the appropriate literature.
1. Suprameatal area of petrosal: 0, low; 1, high. Luo and Gingerich (1999) gave accurate descriptions of the petrotympanic
complexes of early cetaceans. They showed that in basilosaurids the suprameatal area of the petrosal is high and flat-toslightly concave. Sanders and Barnes (2002a, b) described this
same condition in Oligocene baleen-bearing mysticetes. A
high suprameatal area of the petrosal is present in several
Miocene ‘cetotheres’ (see Kellogg 1965, 1968a; Van Beneden
1886) and some balaenids (Bisconti 2003a). In balaenopterids
the suprameatal area of the petrosal is comparatively lower
(Bisconti 2001).
BISCONTI: DIMINUTIVE PLIOCENE WHALE
8. Foramen ‘pseudo-ovale’: 0, absent; 1, present and perforating
styliform process of squamosal (Barnes et al. 1994).
9. Sternum: 0, formed by manubrium and several seternebra; 1,
formed by manubrium only. In archaeocetes and odontocetes,
the sternum is formed by manubrium and some sternebra
(Kellogg 1936) whereas in mysticetes it includes the manubrium only (Tomilin 1967).
10. Number of ribs attached to the sternum: 0, several pairs; 1,
one pair (True 1904; Tomilin 1967).
11. Teeth in the adult: 0, present; 1, absent (Messenger and
McGuire 1998).
12. Dental generations developed during embryology: 0, polyophiodonty; 1, monophiodonty (Messenger and McGuire
1998).
13. Baleen plates: 0, absent; 1, present (Messenger and McGuire
1998).
14. Lateral squamosal crest: 0, absent; 1, present. The lateral
squamosal crest is observed on the dorsal edge of the zygomatic process of the squamosal and anterior to the caudal
apex of the lambdoidal crest in mysticetes; the term is used
by Kellogg (1965, 1968a).
15. Cranio-mandibular joint: 0, dentary and squamosal closely
articulate each other; 1, dentary and squamosal are not closely articulated. In baleen-bearing mysticetes, the glenoid
fossa of the squamosal is a wide concavity, which is not as
closely articulated with the dentary as in terrestrial mammals
and in archaeocete and odontocete cetaceans (Sanderson
and Wassersug 1993); however, it seems that a close articulation of dentary and squamosal was present in the toothed
mysticete Aetiocetus polydentatus (Barnes et al. 1994).
16. Angular process of dentary: 0, high; 1, low; 2, very low. In
archaeocetes, toothed mysticetes, and eschrichtiids the angular process of the dentary is well developed. In balaenids
and ‘cetotheres’ it is lower (Bisconti 2000). In balaenopterids, the angular process is strongly reduced (Lambertsen
et al. 1995).
17. Angular process of dentary in lateral view: 0, squared,
robust, pterygoid groove absent; 1, round, slightly-built,
pterygoid groove absent; 2, squared, slightly-built, pterygoid
groove present. A round angular process is present in Balaenidae (Bisconti 2000, 2003a). In balaenopterids, the angular process is rectangular and is separated from the
condylar area through a pterygoid groove Lambertsen et al.
1995).
18. Supraorbital process of frontal: 0, short; 1, long. In archaeocetes and some ‘cetotheres’ (such as the skull USNM
187416 of Cetotherium megalophysum) the supraorbital process of the frontal is short. In the mysticetes included in this
work, it is longer (Bisconti 2003b).
19. Supraorbital process of frontal: 0, broad; 1, slender; 2, very
broad. In archaeocetes, the supraorbital process of the frontal is broad; in mysticetes it is usually slender; in balaenopterids it is very broad, allowing for the attachment of the
anterior portion of the muscle temporalis (Lambertsen et al.
1995; Zeigler et al. 1997).
20. Supraorbital process of frontal: 0, horizontal; 1, gently descending from the interorbital region of frontal; 2, abruptly
depressed. The supraorbital process of the frontal is abruptly
21.
22.
23.
24.
25.
26.
27.
813
depressed from the interorbital region of the frontal in balaenopterids, eschrichtiids, and related taxa. In ‘cetotheres’
and balaenids it gently descends from the interorbital region
(Zeigler et al. 1997).
Internal opening of facial canal coalesces into the internal
acoustic meatus during early ontogeny: 0, yes; 1, no. Bisconti (2001) demonstrated that the internal acoustic meatus
and the internal opening of the facial canal are separate in
the early ontogeny of Balaenoptera physalus. Subsequently,
Bisconti (2003b) extended this observation to Balaenoptera
edeni and B. borealis. These formations coalesce during the
late ontogeny of balaenopterids. In archaeocetes, balaenids
and ‘cetotheres’, the internal opening of the facial canal does
not coalesce and both are included in a common cavity at
least during the latest ontogeny (Geisler and Luo 1996; Luo
and Gingerich 1999; Bisconti 2003a). The coalescence is
absent in Caperea marginata.
Sagittal crest on the anteriormost portion of the supraoccipital: 0, absent; 1, present. A sagittal crest is observed in
aetiocetids, some ‘cetotheres’ (including Parietobalaena
palmeri), neobalaenids, and in an Eubalaena sp. from the
Pliocene of Tuscany (Bisconti 2002).
Ascending process of the maxilla: 0, absent; 1, definite and
long. State 1 is typical of Balaenopteridae, Eschrichtiidae,
and some advanced ‘cetotheres’ including Cetotherium rathkei (Tomilin 1967; Pilleri 1986, his fig. 15, p. 25). In other
‘cetotheres’ (including Parietobalaena palmeri), the ascending
process of the maxilla is tapered and broad (Sanders and
Barnes 2002b). In balaenids and neobalaenids, the ascending
process of the maxilla is short and not as definite as in the
above taxa (Tomilin 1967).
Interorbital region of frontal: 0, present; 1, absent. In balaenopterids and some late ‘cetotheres’ (such as Cetotherium
rathkei), the ascending processes of the maxillae superimpose onto the interorbital region of the frontal; therefore,
this region is obliterated. In the other mysticetes and archaeocetes this region is not obliterated because the ascending
processes of the maxillae are short or absent (Bisconti
2003b).
Posterior apex of the ascending process of maxilla: 0, anterior and far to postorbital corner of frontal; 1, close to postorbital corner. In early ‘cetotheres’, such as Parietobalaena
palmeri, Diorocetus hiatus and Pelocetus calvertensis, the
ascending process of the maxilla is slightly superimposed
onto the anteromedial portion of the interorbital region of
the frontal and its posterior apex does not move far posteriorly. In balaenopterids and later ‘cetotheres’ (such as Cetotherium rathkei), the posterior apex of the ascending process
of the maxilla is very posterior on the dorsal wall of the
skull.
Squamosal cleft: 0, absent; 1, present. The squamosal cleft is
a widely distributed character observed in several mysticete
taxa such as Neobalaenidae, Balaenopteridae and Eschrichtiidae.
Shape of zygomatic process of squamosal in lateral view: 0,
elongated, slender and subtle; 1, crescent-shaped; 2, slightly
pointed or round; 3, sharply triangular. In archaeocetes and
early ‘cetotheres’ (such as Parietobalaena palmeri) the zygo-
814
28.
29.
30.
31.
32.
33.
34.
PALAEONTOLOGY, VOLUME 48
matic process of the squamosal is usually slender (see, e.g.,
Kellogg 1936, fig. 3, p. 23 and fig. 31a, p. 108). In balaenopterids, the zygomatic process of the squamosal is curved
ventrally and this gives the process a crescent shape (True
1904, pls 3–4, 26–27, 31). This shape is also shared by the
aetiocetid Aetiocetus polydentatus (Barnes et al. 1990) and
the Oligocene baleen bearing mysticetes Micromysticetus rothauseni and Eomysticetus whitmorei, together with an
unnamed Oligocene mysticete from Japan (Sanders and Barnes 2002a, b; Okazaki 1994). In balaenids and neobalaenids
the zygomatic process of the squamosal is stocky (see True
1904, pls 43–44; Baker 1985). In eschrichtiids the zygomatic
process of the squamosal is triangular in lateral view (True
1904, pl. 47).
Position of the posterolateral corner of the exoccipital relative to the posterior border of the postglenoid process in
ventral view: 0, close and posterior; 1, close and medial; 2,
far and posterior (Bisconti 2003b). In archaeocetes and Oligocene baleen-bearing mysticetes the posterolateral corner
of the exoccipital is close and posterior to the posterior
border of the postglenoid process of the squamosal. In eschrichtiids and some ‘cetotheres’, such as Cetotherium rathkei and Mixocetus elysius (Kellogg 1934), this condition is
emphasized being the posterolateral corner of the exoccipital located far to the posterior of the posterior border of
the postglenoid process (state 3). In the other mysticetes
the posterolateral corner of the exoccipital is located closer
(state 1).
Manus: 0, short; 1, long; 2, wide. A long manus is typical of
Balaenopteridae whereas a wide manus is observed in the
living Balaenidae (Tomilin 1967).
Shape of the anterior process of the petrosal in dorsal view:
0, round; 1, squared; 2, triangular. Bisconti (2001, 2003a),
Van Beneden (1878, 1880, 1886), Kellogg (1936, 1965,
1968a), and Sanders and Barnes (2002a, b) gave adequate
descriptions of the morphology of the anterior process of
the petrosal in mysticetes and archaeocetes.
Parietal exposition at the cranial vertex: 0, absent; 1, present,
parietal under the supraoccipital (Balaenoidea); 2, present,
parietal divided posteriorly by the interposition of the supraoccipital (Balaenopteridae, Eschrichtiidae, ‘cetotheres’). In
balaenids and neobalaenids the supraoccipital superimposes
the parietal and the posteromedial portion of the interorbital
area of the frontal (Bisconti 2002). In balaenopterids, eschrichtiids and ‘cetotheres’ the supraoccipital is interposed in
between the parietals.
Position of coronal suture: 0, anterior to the anterior border
of the supraoccipital; 1, posterior. As a consequence of the
superimposition of the supraoccipital onto the parietal and
the posteromedial region of the interorbital area of the frontal, the coronal suture is posterior to the anterior border of
the supraoccipital in balaenids and neobalaenids (Bisconti
2002, 2003b).
Main orientation of the squamosal: 0, horizontal; 1, dorsoventral (McLeod et al. 1993; Bisconti 2000, 2003a).
Dorsoventral compression of tympanic bulla: 0, absent; 1,
present (generates a shallow tympanic cavity) (McLeod et al.
1993; Bisconti 2003a).
35. Extremely low conical process of tympanic bulla: 0, no; 1,
yes. State 1 observed in balaenids and neobalaenids only
(Bisconti 2003a).
36. Tympanic bulla transversely enlarged: 0, no; 1, yes. State 1
observed in balaenids and neobalaenids only (Bisconti
2003a).
37. Internal opening of facial canal: 0, wide, broad and shallow;
1, small, cylindrical and deep (Geisler and Luo 1996).
38. Length of the zygomatic process of squamosal: 0, long; 1,
short; 2, very short. A short zygomatic process of the squamosal is observed in eschrichtiids and such ‘cetotheres’ as
Cetotherium rathkei. In these taxa, however, a zygomatic
process of the squamosal can be easily distinguished. In
balaenids and neobalaenids the zygomatic process of the
squamosal is even shorter and somewhat vestigial (McLeod
et al. 1993).
39. Cervical vertebrae: 0, free; 1, fused. State 1 observed in
balaenids and neobalaenids only (McLeod et al. 1993).
40. Rostral arch: 0, absent; 1, rostrum slightly arched; 2, rostrum
highly arched. State 1 is observed in eschrichtiids only
(McLeod et al. 1993). The rostrum as a whole is highly
curved in Neobalaenidae and Balaenidae; a detail of the curvature (the curve of the premaxilla) is treated in character
62.
41. Coronoid process of dentary: 0, present; 1, absent. The coronoid process is absent in eschrichtiids, balaenids, and neobalaenids (McLeod et al. 1993).
42. Mandibular condyle: 0, articular surface dorsal; 1, articular
surface posterior. State 1 is observed in eschrichtiids, balaenids, and neobalaenids (McLeod et al. 1993).
43. Height of neurocranium: 0, low; 1, high. In balaenids the
neurocranium is high due to the enormous curvature of the
rostrum. This character is absent in other mysticetes
(McLeod et al. 1993).
44. Rostrum transversely compressed: 0, yes; 1, no, rostrum flat
(McLeod et al. 1993).
45. Mylohyoidal sulcus along the ventromedial surface of the
dentary: 0, absent; 1, present (McLeod et al. 1993).
46. Anterior torsion of the dentary: 0, absent; 1, present
(McLeod et al. 1993).
47. Infundibulum: 0, absent; 1, complete; 2, incomplete. State 2
is observed in balaenids only (Fraser and Purves 1960).
48. Posterior extension of the palatine: 0, anterior to posterior
border of the skull; 1, very close to the posterior border of
the skull. State 1 observed in balaenids only (Fraser and Purves 1960).
49. Ventral lamina of the pterygoid: 0, absent; 1, present. State 1
observed in balaenids only (Fraser and Purves 1960).
50. Pterygoid partially covered by the palatine: 0, no; 1, yes
(Fraser and Purves 1960).
51. Stylomastoid fossa: 0, absent; 1, deep as a notch; 2, long and
shallow. The stylomastoid fossa is shaped as a deep notch in
several ‘cetotheres’ (e.g. Parietobalaena palmeri, Diorocetus
hiatus) and balaenopterids (Bisconti 2003b). In balaenids it
occupies a long portion of the posterior process of the periotic and is shaped as a shallow concavity (Bisconti 2003a).
52. Oval window: 0, elliptical; 1, dorsoventrally compressed. In
all the balaenids included into this analysis, the oval window
BISCONTI: DIMINUTIVE PLIOCENE WHALE
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
is markedly compressed along the dorsoventral axis (Bisconti
2003a).
Lateral projection of the anterior process of petrosal: 0,
absent; 1, present and short; 2, present, triangular and long.
The triangular projection of the anterior process of the petrosal is well marked in living and fossil Balaenidae. It is not
preserved in Balaenula astensis and B. balaenopsis (Bisconti
2003a; see also Geisler and Luo 1996).
Baleen plate length: 0, baleen short; 1, long (Eschrichtiidae,
Neobalaenidae); 2, very long (Balaenidae) (McLeod et al.
1993).
Glenoid fossa of squamosal: 0, short and concave; 1, flat-toslightly concave; 2, highly concave and long. State 1 is
observed in balaenids, neobalaenids, eschrichtiids, and ‘cetotheres’. State 2 is typical of Balaenopteridae.
Relative position of zygomatic process of squamosal and
postglenoid process: 0, postglenoid process lower than the
zygomatic process; 1, postglenoid process on the same horizontal plane as zygomatic process. In balaenopterines
and megapterines the postglenoid process is lower than the
zygomatic process of the squamosal (see True 1904, pls 3–4,
26–27, 31).
Distal presence of the ascending temporal crest on the
supraorbital process of the frontal: 0, yes; 1, no. The crest is
absent in Caperea marginata, Morenocetus parvus and in
Balaenella and Balaena (see also Bisconti 2003a).
Lateral process of maxilla in lateral view: 0, anterior to the
supraorbital process of frontal; 1, under the supraorbital
process of frontal (Bisconti 2003a).
Supraorbital process of the frontal: 0, transverse to the long
axis of the skull; 1, directed posteriorly (McLeod et al.
1993).
Anterior process of the supraoccipital: 0, round and wide; 1,
squared and transversely constricted; 2, squared; 3, triangular; 4, narrowly rounded. This character accounts for the
morphological diversity of the anterior portion of the supraoccipital in mysticetes. State 1 is observed in Balaenella and
Balaena montalionis; state 2 is present in balaenopterids;
state 3 is found in ‘cetotheres’; state 4 is seen in Balaenula.
Position of the glenoid fossa relative to the posterior apex of
the lambdoidal crest: 0, glenoid fossa located below the
lambdoidal crest; 1, anterior; 2, posterior. The character is
related to Bisconti’s (2003a) diagnosis of Balaenula.
Curvature of premaxilla: 0, no curvature; 1, regular curvature; 2, irregular curvature. In Balaenula astensis and Eubalaena the anterior 25 per cent of the premaxilla is directed
ventrally, interrupting the regular curvature of the rostrum
in that region (Bisconti 2000, 2003a).
Curvature of the dorsal surface of the skull: 0, skull mainly
straight; 1, regular curvature; 2, irregular curvature. A regu-
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
81.
82.
815
lar curvature is observed in Balaena and Balaenella. Irregular
curvature is present in Eubalaena and Balaenula (McLeod
et al. 1993).
Distal portion of the infraorbital plate of the maxilla: 0, present; 1, absent (Bisconti 2003a).
Orientation of the nasals and the proximal rostrum: 0,
onward; 1, upward. State 1 is present in Balaena mysticetus,
B. montalionis and, presumably, in B. ricei (Bisconti 2003a).
Relief on the parietal squama: 0, absent; 1, present (Bisconti
2000, 2003a).
Spreading of the anterolateral portion of the parietal onto the
emergence of the supraorbital process of the frontal: 0,
absent; 1, present. The spreading of the parietal onto the
emergence of the supraorbital process of the frontal is
observed in Balaenula and Eubalaena among the Balaenidae
(Bisconti 2003a).
Dome on the supraoccipital: 0, absent; 1, present (Bisconti
2002).
Posterior outline of the exoccipital in lateral view: 0, round;
1, squared. Squared exoccipitals are observed in Eubalaena
skulls (Bisconti 2000, 2003a).
Position of the glenoid fossa of the squamosal relative to the
orbit: 0, posterior; 1, under the orbit. State 1 is diagnostic of
Balaenula (Bisconti 2003a).
Height of the ventral surface of the exoccipital: 0, higher
than the orbit; 1, at the level of the orbit. State 1 is diagnostic of Balaenula (Bisconti 2003a).
Height of the ascending temporal crest: 0, low; 1, high. A
high ascending temporal crest is observed in Balaenula (Bisconti 2003a).
Hypoglossal foramen: 0, present; 1, absent. The presence of
the hypoglossal foramen is known in Balaenula astensis (Bisconti 2000, 2003a).
Olecranon: 0, present; 1, absent.
Acromion: 0, present; 1, absent.
Coracoid: 0, present; 1, absent.
Shape of the scapula: 0, high and short; 1, high and long.
Antibrachium: 0, shorter than humerus; 1, longer than
humerus. See Westgate and Whitmore (2002) for a discussion of this character.
Radius: 0, straight; 1, highly convex. The radius is anteriorly
convex in living balaenids and in Balaena ricei (see Pilleri
1987; Benke 1993; Westgate and Whitmore 2002).
Pars cochlearis: 0, transversely short; 1, protruded cranially.
A cranial protrusion of the pars cochlearis is observed in
balaenopterids and in the living Eubalaena glacialis (Bisconti
2001, 2003a).
Groove for the tensor tympanic muscle: 0, present; 1, absent
(Luo and Gingerich 1999).
816
PALAEONTOLOGY, VOLUME 48
Character · taxon matrix used in the phylogenetic analysis
Protocetus atavus
Zygorhiza kochii
Aetiocetus polydentatus
Parietobalaena palmeri
Eschrichtius robustus
Balaenoptera physalus
Megaptera novaeangliae
Caperea marginata
Morenocetus parvus
Eubalaena glacialis
Eubalaena belgica
Balaenula balaenopsis
Balaenula astensis
Balaenula sp. (Japan)
Balaenella brachyrhynus
Balaena montalionis
Balaena ricei
Balaena mysticetus
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