Supplementary information for:
Schneider et al. Ferns diversified in the shadow of angiosperms.
A re-evaluation of the fossil record of major fern lineages and a synopsis of fossil fern constraints applied in this study.
Recent reviews of the fossil record of ferns served as an excellent basis for this study (Cleal 1993; Taylor & Taylor 1993; Tidwell & Ash 1994;
Collinson 1996, 2001, 2002; Rothwell 1996 a, b; Kenrick & Crane 1997; Skog 2001; Stewart & Rothwell 2001; Deng 2002; Van Konijnenburg-van
Cittert 2002; Wang 2002). However, because we assigned fossils to extant clades based on the presence of synapomorphic character states and
by taking into account our current understanding of fern phylogeny (Hasebe et al. 1995; Kenrick & Crane 1997; Pryer et al. 1995; Schneider 1996;
Stevenson & Loconte 1996; Pryer et al. 2001; results presented in this study) our interpretation of some fossils differs from published
interpretations (see Table 1 below). Some published assignments are questionable because they are based on putatively plesiomorphic or
homoplastic features. For example, characters used by previous authors to assign the Mesozoic form-genus Coniopteris to Dicksoniaceae are not
synapomorphies for the Dicksoniaceae, but are putatively plesiomorphic character states for the stem group of tree ferns + polypodiaceous ferns.
In addition, the form-genus Coniopteris may be polyphyletic, with some species of Coniopteris belonging to the Dicksoniaceae, and others
belonging to basal polypodiaceous fern lineages (Samylina 1976; Lovis 1977; Schneider & Kenrick 2001). We did not accept the assignments of
several polypodiaceous fossils to extant genera because the evidence provided is inconclusive with respect to extant fern morphologies. In some
cases, the features described in a fossil are present in various genera of polypodiaceous ferns and did not allow unambiguous identification of a
fossil with a particular extant genus. For example, several fossils that had been assigned by others to dennstaedtioid ferns display preserved
anatomical features that occur in the basal lineages of the polypodiaceous ferns, including the lindsaeoid, dennstaedtioid, and pteridoid ferns.
Assignment of these fossils to a specific clade is ambiguous despite certain assignment to polypodiaceous ferns. A further source of conflict is the
application of different definitions of taxonomic units such as the family Polypodiaceae. Whereas this term is used today for a particular lineage of
eupolypods (Smith et al., in prep.), in the past it was applied to circumscribe the entire polypod lineage. For example, Leptolepidites is a trilete
spore often assigned to Polypodiaceae sensu lato (e.g., Takahashi 1997), but is characterized by a morphology common in several basal
polypodiaceous clades, including dennstaedtioids in which extant Leptolepia belongs, but rare in Polypodiaceae sensu stricto (as defined in recent
classifications). Fossilized spores represent a major source of information about past fern diversity, but many assignments are ambiguous in light
of the often-ignored morphological similarity of spores within disparate extant fern clades. Laevigatosporites is another fossil spore often assigned
to Polypodiaceae, but similar monolete spores with a psilate to granulate surface also occur in distantly related families (van Uffelen 1991), as well
as in members of the basal polypods, such as dennstaedtioids and lindsaeoids.
In general, the fern fossil record of the Cretaceous and Tertiary is less well known in comparison to the fossil record of angiosperms. This may
be partly due to preservation biases or to particular aspects of the evolution of morphological characters in derived ferns. Ferns lack flowers,
fruits, seeds, and wood – structures that are likely to be preserved or that are very taxonomically informative components of the fossil record of
angiosperms. In addition, the outer part of the spore wall (perine) is frequently lost in fossilized spores. The spore perine is very important in the
taxonomy of modern taxa because it harbors several valuable morphological characters. This lack of preservation is especially disadvantageous if
the complex spore wall ornamentation is exclusively formed by the perine, as is the case in the majority of polypods. In those instances where the
perine is missing, the fossilized monolete or trilete spore shows a psilate exine. The majority of fern macrofossils are leaf impressions that can
rarely be assigned unequivocally to an extant fern lineage. Anatomically preserved fossils provide more information, but the lack of critical
characters, such as soral characters, precludes taxonomic assignment in many cases. The Cretaceous fossil genus Tempskya is such an
example. The stem and root anatomy of these ferns is well preserved, but the relationship of this fossil taxon to extant lineages remains unknown
(Tidwell & Ash 1994; Schneider & Kenrick 2001).
Schneider et al., Supplementary Information on Fossils, pg.2
It is important to note that the references we surveyed did not provide exact age estimates for fossils but instead reported only time intervals at
(predominantly) stage-level resolution. We used the accepted upper boundary of the reported interval as our minimum age estimate. For
example, for a fossil reported from the Albian, we used the upper boundary (99 Ma) as the minimum age assignment in our analyses. This also
applies to the fossil age estimates we used for angiosperms. To be consistent, we used the absolute ages of the upper bound of the time intervals
listed in Magallón & Sanderson (2001), rather than the midpoint of the intervals, as they did. For example, for node B62 (Cucurbitales; Fig. 1),
Magallón & Sanderson (2001) indicate Paleocene, 59.9 (midway through the Paleocene, 65 to 54.8). We used 54.8 as the minimum age
constraint for that node.
Several fossil ferns were not used as minimum age constraints based on one or both of the following reasons: (1) the relevant node was not
well-supported and the next deeper or higher node with Bayesian support ≥95% had an assigned fossil with an older age, (2) a sister clade had a
fossil assignment with an older age. For example, the schizaeaceous fossil ferns (e.g., Klukia, Klukiopsis, Stachypteris; Deng & Wang 2000; Skog
2001; Van Konijnenburg-van Cittert 2002; Wikström et al. 2002) were not used despite their excellent fossil record (since the early Jurassic)
because the node at that divergence had low support. Several polypodiaceous fern genera that are known from the Tertiary (Middle and/or Late
Eocene) were not used as time constraints although they are unequivocal members of modern families such as Athyriaceae [Makopteris],
Dryopteridaceae [Rumohra], Polypodiaceae [Pseudodrynaria], and Thelypteridaceae [Cyclosorus and Pneumatopteris] (Barthel 1976; van Uffelen
1991; Wilde & Frankenhäuser 1998; Stockey et al. 1999; Collinson 2001).
Schneider et al., Supplementary Information on Fossils, pg.3
Table 1. Fossil age constraints used in the fern and angiosperm (only nodes B01, B02, B05) analyses (geological timescale according to the
Geological Society of America 1999). Node numbers correspond to Figure 1A (1B). For remaining constraints used in the angiosperm analysis,
see Magallón & Sanderson (2001)a. Fossils were only assigned to nodes with Bayesian support ≥0.95. They were assigned to nodes based on the
presence of apomorphic character states that provide unequivocal evidence for the assignment of a fossil to one of the lineages derived from a
particular node (crown group assignment). If we were unable to reject the possibility that the reported character state could be a synapomorphy
for the whole lineage, including crown and stem groups, the fossil was assigned to the next deeper well-supported clade (stem group assignment).
Node
Lineage name
(if applicable)
Fossil age and
minimum age
assignment (Ma)
Fossil(s)
Synapomorphy References
Comment on fossils pertinent to nodes in Figure 1, indicating
which fossils were selected as minimum ages for particular
nodes
A01
B01
Euphyllophytes
Eifelian (380)
Ibyka
Crossia
Position of
protoxylem in
mature stele
(mesarch in
Ibyka, endarch
in Crossia)
Kenrick &
Crane 1997
The oldest euphyllophyte fossils date back to the early Devonian
(Psilophyton), but the appearance of fossils such as Ibyka and
Crossia marks the split of two extant lineages of euphyllophytes
(monilophytes and spermatophytes) at the end of the Middle
Devonian. Ibyka is accepted here as a member of the
monilophytes but not as a member of the horsetail lineage.
Crossia is the oldest fossil of the radiophytes (the stem group of
spermatophytes).
A02
B05
Seed plants
Pennsylvanian
(310)
Oldest conifers
Cones, twigs
Miller 1999
These fossils are the oldest unequivocal remains of an extant
lineage of seed plants and indicate that the origin of conifers and
their divergence from other seed plant lineages occurred at least
in the Late Carboniferous.
A03
B02
Monilophytes
Tournaisian (354)
Archaeocalamites Stem anatomy
Senftenbergia
of the Equisetum
type (Archaeocalamites) or
sporangia as in
leptosporangiate
ferns
(Senftenbergia)
Bateman
1991; Galtier
& Philips
1996; Bek &
Psenicka
2001
The oldest remains of the extant lineages of monilophytes date
back to the earliest Carboniferous. Archaeocalamites and
relatives are accepted here as the oldest unequivocal members of
the extant horsetail lineage and are used here to mark the earliest
divergence within monilophytes. The oldest leptosporangiate
ferns also date back to the Early Carboniferous. They are likely
members of the stem group of extant leptosporangiate ferns, and
cannot be assigned to any modern lineage.
A04
Leptosporangiate Late Permian (280) Grammatopteris
ferns
Roessler &
Galtier 2002;
Skog 2001
The osmundaceous ferns are the most basal lineage of crown
group leptosporangiate ferns. The oldest relatives of the lineage
date back to the Early Permian. They have an extensive fossil
record from the Late Permian. They are often assigned to the
family Guiareaceae.
A05
a
Middle Permian
(270)
Oligocarpia
Szea
Stele
organization of
the
osmundaceous
type
Structure of the Wang et al.
spore wall and 1999; Yao &
petiole anatomy Taylor 1988
The spores of Oligocarpia and Szea share certain characters with
the extant gleicheniaceous ferns. The leaf morphologies of
Oligocarpa and Szea do not indicate a close relationship to any
extant member of the gleicheniaceous lineage. Therefore, these
To be consistent, we used the absolute ages of the upper bound of the time intervals listed in Magallón & Sanderson (2001), rather than the midpoint of the intervals, as they did.
Schneider et al., Supplementary Information on Fossils, pg.4
taxa are likely stem group members of the gleicheniaceous ferns.
These fossils are assigned here to node A05 rather than to the
node corresponding to the divergence of gleicheniaceous ferns
because that node is not well-supported. Node A05 includes also
the filmy ferns, which have a particularly poor fossil record. The
fossil Hopetedia is the oldest known record of the filmy fern
lineage and dates from the Late Triassic (Axsmith et al. 2001).
A07
A09
Water ferns
Berriasian (137)
Regnellites
nagashimae
Similarities in
leaf and stem
morphology to
extant genera
Yamada &
Kato 2002
The authors demonstrate that this fossil is part of the
Marsileaceae lineage.
Middle to Late
Jurassic (159)
Cyathocaulis
Anatomy of the
stele is similar to
extant scaly tree
ferns
Tidwell &
Nishida 1993;
Lantz et al.
1999; Skog
2001; Stewart
& Rothwell
2001
Many reviews accept a Triassic origin for the tree ferns based on
similarities of Triassic and Jurassic fossils to extant
Dicksoniaceae. These reviews especially emphasize the sorus,
but ignore the occurrence of similar soral structures in basal
polypodiaceous ferns such as dennstaedtioids. Samylina (1976)
reported remarkable similarities of Coniopteris dicksonioides from
the Early Cretaceous with the extant genus Sphenomeris in the
lindsaeoid ferns (see further discussion in Schneider & Kenrick
2001). Recent phylogenetic studies (Pryer et al. 2001) have
demonstrated a sister group relationship between tree ferns and
polypodiaceous ferns. The soral characters that have been used
to define Dicksoniaceae in the paleobotanical literature are likely
to be plesiomorphic for the larger clade of tree ferns +
polypodiaceous ferns. Therefore, the possibility exists that some
fossils, especially members of Coniopteris, may be the remains of
either tree ferns, or basal polypodiaceous ferns, or of the stem
groups of these ferns. In addition, phylogenetic studies indicate
that the Dicksoniaceae is likely paraphyletic in its current
circumscription. To avoid these problems, we use here the oldest
fossil of the certainly monophyletic Cyatheaceae (Cyathocaulis) to
provide a minimum age within tree ferns. As shown by Lantz et al.
(1999), other Jurassic tree fern fossils may be related to extant
Dicksoniaceae and form a dicksoniaceous grade from which the
Cyatheaceae were derived. A recent study gave further
unequivocal evidence for the occurrence of Cyatheaceae in the
Early Cretaceous based on fossils with preserved soral structures
(Smith et al. 2003). Members of the sister clade (node A08,
Plagiogyria and the related family Loxomataceae) have a less
complex stem anatomy than members of the Cyathea/Dicksonia
clade. The genus Plagiogyria lacks a fossil record, but its putative
sister clade (Loxomataceae) is known from Early Cretaceous
fossils (Skog 2001). These Loxomataceae fossils, however, are
Schneider et al., Supplementary Information on Fossils, pg.5
younger than the oldest certain fossils of the Cyatheaceae.
A10
Polypods
A11
A14
Dennstaedtioids
Neocomian (121)
Various
Sporangia with a Chen et al.
vertical, broken 1997; Deng
annulus
2002
The oldest putative member of the polypodiaceous ferns is
Aspidistes thomasii from the Middle Jurassic (Lovis 1977; Cleal
1993). However, the position of the taxon is ambiguous because
critical synapomorphic characters, such as the position of the
annulus, are not preserved. We accept here the arguments of
Collinson (1996) that this fossil cannot be accepted as definitely
belonging to this fern lineage. Deng and Chen et al. described
fossils from Lower Cretaceous sediments of Northern China that
possess broken vertical annuli. These fossils are the first
unequivocal polypodiaceous ferns and we use them here to
constrain this node. Their precise relationships within polypods,
however, are uncertain. Deng and Chen et al. assigned them to
several derived modern genera, but their evidence is inconclusive.
These very important fossils need further study. The reported
diversity in China contrasts strongly with the poor record of
polypodiaceous ferns elsewhere throughout the Cretaceous.
Albian (99)
Lindsaeoid fossil
Root cortex
Schneider &
structure shows Kenrick 2001
a character
combination (6
cells in the inner
cortex +
sclerenchymatous outer
cortex) that is
unique to
lindsaeoid ferns
Based on a root anatomical apomorphy, this fossil gives
unequivocal evidence for the presence of lindsaeoid ferns in the
Early Cretaceous. Unfortunately, nothing else is known about the
fossil, and therefore it does not provide evidence for the
diversification of extant taxa of lindsaeoid ferns. All critical
features of the root anatomy are identical among extant lindsaeoid
ferns, and the fossil may be either a member of the stem group or
crown group of this clade. Therefore, we do not assign it to the
crown group (node A12) but to the next deeper and wellsupported node (A11). As discussed in Schneider & Kenrick
(2001), fossils showing convincing similarities in leaf shape and
position of the sori to extant lindsaeoid ferns were reported from
the Early Cretaceous of Siberia (Samylina 1976). Several authors
compared the Early Cretaceous fossil Adiantites lindsayoides with
extant lindsaeoid ferns (Seward 1904; Lovis 1977; Tidwell & Ash
1994), but the reported evidence is insufficient to accept its
assignment to lindsaeoids (Douglas 1973; Drinnan & Chambers
1986; Schneider & Kenrick 2001).
Middle Eocene
Dennstaedtia-like Shape of the
fossils
indusia,
anatomical
features of the
rhizome
Collinson
2001
Fossils pertinent to this node were not used as time constraints.
Fossils that show characters of Dennstaedtia and its close
relatives occur in sediments from the Middle Eocene onward.
Some of these are likely parts of other clades such as Dennastra,
a putative relative of Saccoloma. Several dennstaedtioid-like
fossils occur in the Late Cretaceous and Tertiary, but their exact
relationships are ambiguous. Similar anatomical features occur in
Schneider et al., Supplementary Information on Fossils, pg.6
related families, especially pteridoid ferns.
Cenomanian (93.5) Pteris sp.
Leaf shape and Krassilov &
This leaf impression is likely the oldest known fossil of the
the presence of Bacchia 2000 pteridoid fern lineage. It cannot be assigned unequivocally to any
pseudoindusia
extant lineage of pteridoid ferns. Therefore, we interpret it as a
stem group member of the pteridoid ferns and assign it to node
A15. The shape of the pinnae and the pseudoindusia-like
impressions resemble leaves of pteridoid ferns, especially
cheilanthoids, but no further assignment is possible with the
existing material and the currently existing phylogenetic
hypothesis for this clade.
A17
Middle Eocene (37) Hewardia regia
Dimidiate pinnae Collinson
with adiantioid
2001
pseudoindusia
These Adiantum-like fossils are likely the oldest known remains of
the clade comprising cheilanthoid and adiantoid ferns. The
occurrence of dimidiate pinnae with adiantioid pseudoindusia
supports assignment to the extant genus Adiantum (node A18),
but we assign it to node A17 to reflect uncertainty in the currently
available phylogenetic hypotheses concerning the evolution of the
pteridoid ferns, especially the uncertainty in relationships of the
monotypic genus Rheopteris that has characters of both the
vittarioid and the Adiantum clades.
A19
Maastrichtian (65) Acrostichum
Anatomical
Bonde &
features that are Kumaran
known only from 2002
Acrostichum
This fossil shows many characteristics of Acrostichum, but it is not
clear if these characters are synapomorphic for the genus
Acrostichum or for the Acrostichum/Ceratopteris clade (node
A20). We assign the fossil to node A19, because it has
characters that likely evolved earlier than the split between the
two extant genera Acrostichum and Ceratopteris. This fossil has
some diagnostic anatomical features, whereas Paleocene fossils
assigned to Acrostichum are often only leaf impressions with
anastomosed venation strongly resembling extant Acrostichum,
but they could be remains of close relatives of the Acrostichum/
Ceratopteris clade. Similar venation patterns are found in Pteris
holttumii and the monotypic pteridoid genus Neurocallis.
A20
Middle Eocene
Magnastriatites
Spore
ornamentation
Dettmann &
Clifford 1991,
1992;
Collinson
2001
Fossils pertinent to this node were not used as time constraints.
Spores assigned to the fossil form-genus Magnastriatites strongly
resemble spores of extant Ceratopteris. Hence they support the
occurrence of Ceratopteris following the divergence of the two
extant genera, Ceratopteris and Acrostichum (which has very
different spores).
Middle Eocene
Rumohra
Leaf and sorus
shape
Collinson
2001; Wilde &
Frankenhäuser 1998
Fossils pertinent to this node were not used as time constraints.
Fossils that are remarkably similar to modern Rumohra and
related dryopteridoid ferns are reported from several localities in
the Middle Eocene.
A15
A21
Derived ferns
Eupolypods
Schneider et al., Supplementary Information on Fossils, pg.7
A24
A25
Eupolypods II
Late Eocene
Pseudodrynaria
Shape of the
Van Uffelen
pinnae
1991
combined with
the arrangement
of the sori
Fossils pertinent to this node were not used as time constraints.
The oldest generally accepted fossil within this lineage (node A24)
is from the Late Eocene. Recently reported fossils from the
Middle Eocene are based on inconclusive evidence because
similar structures are found in other eupolypod genera.
Middle Eocene
Cyclosorus
striatus
Pneumatopteris
Venation with
secondary veins
arising from
fusion of veins
from adjacent
vein groups
(Cyclosorus,
Pneumatopteris)
Anatomical
features of the
petiole, rhizome,
and root
(Makopteris).
Barthel 1976;
Stockey et al.
1999;
Collinson
2001
Fossils pertinent to this node were not used as time constraints.
The venation (goniopteroid or meniscioid) supports the
unequivocal assignment of two of these fossils (Cyclosorus,
Pneumatopteris) to the Cyclosorus lineage within the
Thelypteridaceae. Anatomical features provide unequivocal
evidence for close relationships of the third fossil, Makopteris, to
extant species of the athyrioid fern genera Athyrium and
Diplazium.
Shape and
position of the
elonagte,
indusiate sorus
Collinson
2001
Fossils pertinent to this node were not used as time constraints.
These are the oldest fossils that can be assigned unequivocally to
asplenioid ferns using characteristics such as shape of the
indusiate sori, venation, and shape of the blade. These fossils
cannot be assigned to a clade of extant asplenioid ferns because
key features are missing in the fossil record.
Makopteris
Asplenium-like
fossils
A26
Middle Eocene
A29
Onoclea
Campanian/
Maastrichtian (65) Woodwardia
Leaf shape
combined with
venation
patterns
Upchurch &
Mack 1998;
Rothwell &
Stockey 1991;
Pigg &
Rothwell 2001
Leaf impressions assignable to the extant genera Onoclea and
Woodwardia in the uppermost Cretaceous are very convincing
because these fossils so strongly resemble the form of the
modern taxa. In addition, these genera have a good fossil record
from their first occurrence in the Late Campanian/Maastrichtian to
the Eocene. The reported characters of the Woodwardia-fossil
from the Late Cretaceous and Early Paleocene did not allow the
assignment to any extant species of Woodwardia and we cannot
rule out the hypothesis that this fossil represents a blechnoid fern
stem lineage (node A30). The oldest Woodwardia-fossil
assignable to an extant species (W. virginica) is from the Miocene
(Pigg & Rothwell 2001).
A30
Middle Eocene (37) Blechnum
dentatum
Leaf shape
combined with
the position of
the elongate,
indusiate sorus
Collinson
2001
The fossil record indicates the first appearance of the blechnoid
ferns in the Late Cretaceous (see node A29) but the oldest fossil
of the genus Blechnum is known only from the Middle Eocene.
The split between Woodwardia and Blechnum likely happened in
the Paleocene or Eocene (Cranfill 2001).
Schneider et al., Supplementary Information on Fossils, pg.8
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