Downloaded from geology.gsapubs.org on June 15, 2012
Geology
The advent of hard-part structural support among the Ediacara biota:
Ediacaran harbinger of a Cambrian mode of body construction
Erica C. Clites, Mary L. Droser and James G. Gehling
Geology 2012;40;307-310
doi: 10.1130/G32828.1
Email alerting services
click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new
articles cite this article
Subscribe
click www.gsapubs.org/subscriptions/ to subscribe to Geology
Permission request
click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA
Copyright not claimed on content prepared wholly by U.S. government employees within scope of
their employment. Individual scientists are hereby granted permission, without fees or further
requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent
works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms
to further education and science. This file may not be posted to any Web site, but authors may post
the abstracts only of their articles on their own or their organization's Web site providing the posting
includes a reference to the article's full citation. GSA provides this and other forums for the
presentation of diverse opinions and positions by scientists worldwide, regardless of their race,
citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect
official positions of the Society.
Notes
© 2012 Geological Society of America
Downloaded from geology.gsapubs.org on June 15, 2012
The advent of hard-part structural support among the Ediacara biota:
Ediacaran harbinger of a Cambrian mode of body construction
Erica C. Clites1*, Mary L. Droser1, and James G. Gehling2
1
Department of Earth Sciences, University of California, 900 University Avenue, Riverside, California 92521, USA
South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia
2
ABSTRACT
The apparent lack of taxonomic continuity between the Precambrian and Cambrian fossil
records has led to controversial and conflicting interpretations about the Ediacara biota and
their place in the evolution of metazoan life on this planet. This has been further complicated
by the absence of similar modes of construction between these faunas and the rarity of
Precambrian skeletonized fossils. We describe a new Ediacaran organism that represents the
oldest multielement organism with structural support through either biomineralization or
chitin. Coronacollina acula gen. et sp. nov. from the Ediacara Member (Rawnsley Quartzite)
was constructed from a framework of rigid and brittle elements that disarticulated after
death. It reveals a constructional mode not recognized previously among members of this
assemblage, but one that was prevalent among Cambrian organisms. Coronacollina consists
of a truncated cone associated with spicules, up to 37 cm in length, diverging radially from
the cone. This constructional morphology is similar to the Cambrian Choia, a low conical
demosponge with a corona of long spicules, providing a long-predicted constructional link
between the Ediacara biota and the Cambrian fossil record.
INTRODUCTION
The Ediacara biota consist of macroscopic,
morphologically diverse and generally soft-bodied organisms (Xiao and Laflamme, 2009), with
most classified only to the genus and species
level. A few Ediacaran fossils have been interpreted as stem group metazoans, but the Cambrian period marks the unequivocal appearance
of most major phyla. The apparent discontinuity between the Precambrian and the Cambrian
fossil record is largely based on the absence of
skeletal hard parts until the very end of the Ediacaran period and the lack of Cambrian-type constructional morphologies among the Ediacara
biota. With rare exceptions (Conway Morris,
1993; Hagadorn et al., 2000; Jensen et al., 1998;
Lin et al., 2006), fossils of the Ediacara biota are
not found in Cambrian strata, and those that are
reported are typical Ediacara morphologies. For
lack of a strong alternative, much of the biota is,
thus, commonly interpreted to have gone extinct
by the end of the Ediacaran period (Narbonne,
2005; Vickers-Rich and Komarower, 2007), a
view supported by the documented extinction
of a skeletonized genus coincident with the Precambrian-Cambrian boundary (Amthor et al.,
2003) and the decline of acritarchs at this time
(Cohen et al., 2009). Here we report on a new
Ediacaran fossil, Coronacollina acula gen. et
sp. nov., that bears morphological resemblance
to the Cambrian sponge Choia and unlike other
taxa of the Ediacara biota, bore the major evolutionary novelty of structural support.
*Current address: Glen Canyon National Recreation Area, P.O. Box 1507, Page, Arizona 86040,
USA; E-mail: eclites@gmail.com.
GEOLOGIC SETTING
The fossiliferous Ediacara Member of the
Rawnsley Quartzite is located 50–500 m below
a basal Cambrian disconformity (Fig. DR1
in the GSA Data Repository1) and consists of
medium-grained sandstone beds deposited in
shallow marine environments with widespread
microbial mats (Droser et al., 2006). The Ediacara Member fills southeastern-trending paleovalleys cut into the Chace Quartzite Member of
the Rawnsley Quartzite, and is disconformably
overlain by the early Cambrian Uratanna Formation, bearing the first assemblage of complex
trace fossils and rare body fossils (Jensen et al.,
1998; Gehling, 2000). The Rawnsley Quartzite
has not been dated, but the fauna places it within
the White Sea Assemblage (Waggoner, 2003).
A range of undescribed fossil forms has been
revealed during excavation and overturning of
large areas of fossiliferous bed soles near Nilpena, South Australia. These new forms provide
data on new body fossils (i.e., Sappenfield et
al., 2011) and new constructional morphologies not previously recognized. Coronacollina
acula gen. et sp. nov. is described from several
sites in the Flinders Ranges, including Nilpena,
Ediacara Conservation Park, and Bathtub Gorge
(Fig. DR2), from excavated beds and slabs in
float. Fossils are described from latex casts made
of needle-like spicular impressions and external
molds of conical bodies on sandstone bed bases.
1
GSA Data Repository item 2012088, stratigraphic column, locality map, and data tables, is
available online at www.geosociety.org/pubs/ft2012
.htm, or on request from editing@geosociety.org or
Documents Secretary, GSA, P.O. Box 9140, Boulder,
CO 80301, USA.
DESCRIPTION OF FOSSILS
Thirty-two articulated specimens and 338
additional incomplete specimens of Coronacollina acula gen. et sp. nov. were studied on five
separate bedding surfaces. Coronacollina consists of two components: (1) a thimble-like,
truncated cone, with the rim (top outer edge)
diameter slightly smaller than the base, and (2)
narrow, radially arranged spicules (Fig. 1). Spicules found directly associated with cone rims
are here described as articulated, while isolated
spicules are disarticulated. On bed MMS, where
Coronacollina is most abundant, 13 of 269 individuals have one to two articulated spicules, but
up to four spicules have been recorded on specimens on other beds. The cone varies from 1 mm
to 22 mm in diameter and can be up to 15 mm
in height (Tables DR1 and DR2). The cone rim
is threefold. The spicules are commonly <1 mm
wide and up to 370 mm long, and are straight
with rare lenticular sections (Table DR3). Any
deviation from a sharp, straight groove is slight,
and only noticeable when a ruler is placed next
to the groove. Tapering, splaying, widening, or
true curving of spicules is not observed. In the
best-preserved examples, the cone is radially
symmetrical, with a circular to polygonal shallow recess at the top. The periphery of the cone
base is not sharply defined. Irregular specimens
have similar relief and cone shape but lack rims.
Up to four spicules are observed attached at the
cone rim, although additional specimens could
reveal more than four attached spicules.
Smaller cones with threefold rims are the
most commonly recognized form of the Coronacollina body throughout the Flinders Ranges
(Fig. 2). This threefold symmetry appears as
three separate nodes instead of a continuous rim
(Fig. 3). While some large rimmed specimens
of Coronacollina display threefold symmetry, it is more pronounced in small specimens.
Slabs with abundant small Coronacollina specimens are not commonly found with associated
spicular impressions (Fig. 2A), likely because
the spicules were too thin to be molded by the
medium-grained sand of the fossil beds.
PRESERVATION
Coronacollina acula occurs exclusively in
negative hyporelief as a deep subcircular pit
associated with multiple straight grooves (Figs. 1
and 2; Appendix). Small and large Coronacollina specimens were subject to different
© 2012 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org.
GEOLOGY,
April
2012
Geology,
April
2012;
v. 40; no. 4; p. 307–310; doi:10.1130/G32828.1; 3 figures; Data Repository item 2012088.
307
Downloaded from geology.gsapubs.org on June 15, 2012
(rather than a multiple of three), it is the best
reconstruction based on current evidence. The
abundance of disarticulated spicules suggests
that they easily disarticulated and that there
could have been more on the organism.
Beds within the Ediacara Member of the
Rawnsley Quartzite mold the surface of the Ediacaran seafloors and the organisms thereon. Early
diagenesis in the form of a mineralized “death
mask” (Gehling, 1999) has enabled molding of
impressions of resilient elements that did not
collapse or decay immediately after burial, as in
this case, where the body of Coronacollina and
its spicular supports were consistently preserved
as an external mold on bed soles, while evidence
of soft tissue is either absent or present as a diffuse halo. Detailed study of bedding surfaces
indicates that Coronacollina was resting on, or
partly embedded in, microbial mats. The preservation of Coronacollina suggests a rigid body
with lateral support, which prevented its collapse as sediment accumulated around it. With a
relief of up to 1.5 cm, Coronacollina possessed
the highest relief of any Ediacara organism preserved in situ.
Figure 1. Coronacollina acula gen. et sp. nov. Arrows indicate Coronacollina main body.
Scale bars represent 1 cm. The number of articulated spicules is indicated for each specimen below. Additional spicules are present, but these are disarticulated and not included in
the total count. A: Coronacollina SAM P43375, specimen from Ediacara South with four articulated spicules, external mold in rock. B: Latex impression of SAM P43375. C: Two groups
of Coronacollina specimens, most without articulated spicules, NP06, Nilpena. D: Holotype
SAM P43257, an external mold exhibiting both fossil components, Bathtub Gorge. Four articulated spicules extend from the right side of this specimen. E: Coronacollina SAM P43378
associated with three radiating articulated spicules, external mold, Nilpena. F: Latex impression, SAM P43378.
preservational biases. As a result, the largest
cones are more variable in shape than the smaller
specimens, dominantly due to deformation during burial and compaction. Small specimens can
be obscured by the textured organic surface of
the bed, while large specimens are recognizable even when irregularly shaped as a result
of deformation. In addition, articulated spicules
do not cross, while disarticulated spicules can
be broken or crossing. The length distribution
of spicules (Fig. DR3) also suggests that large
308
spicules may break into smaller pieces during
transport. This relatively common separation
of spicular impressions and cones reflects their
preservation beneath storm event beds involving
some distortion or alignment of organisms from
these benthic communities (Tarhan et al., 2010).
Coronacollina is reconstructed in Figure 3
with four spicules, because this is the highest
number of articulated spicules observed in any
specimen. While it is unusual for an organism
with threefold symmetry to have four spicules
PALEOECOLOGY
Within the Ediacara Member, individual beds
display a high degree of heterogeneity in body
fossil assemblages in terms of composition and
abundance (Droser et al., 2006) (Table DR4).
On bed MMS at Nilpena, Coronacollina is the
most abundant fossil, representing 269 of 405
observed fossil specimens. While Coronacollina is found at other localities, nowhere is it
as abundant. The presence of low-relief fossils
such as Dickinsonia and Parvancorina on bed
MMS suggests that localized abundance of
Coronacollina is not due to taphonomic bias but
rather the organism’s patchy distribution on the
Ediacaran seafloor. Coronacollina is most common on beds that represent deposition below
fair-weather wave base.
In life, the spicules appear to have radiated
from the body as support struts, in a manner
similar to the Cambrian sponge, Choia. After
the death of the organism, spicules apparently
disarticulated from the cone and fell to the seafloor. The morphological consistency between
articulated and disarticulated spicules suggests
they were made of a rigid substance, such as
chitin, opaline silica, or calcium carbonate.
DISCUSSION
Coronacollina bears morphological resemblance to Choia, a demosponge with a body
up to 70 mm in diameter and spicules up to
1 mm wide and 80 mm long (Rigby, 1986).
Choia is a low conical to elliptical sponge surrounded by a corona of long spicules, which
radiate from the central disc. Choia specimens
are generally preserved flattened, although in
GEOLOGY, April 2012
Downloaded from geology.gsapubs.org on June 15, 2012
Figure 2. Smaller cones with threefold rims are the most commonly recognized form of Coronacollina acula throughout the Flinders Ranges. Scale bars represent 1 cm. A: Several dozen
Coronacollina specimens without preserved articulated spicules, SAM P46306, East Mount
Scott Range. B: Several Coronacollina specimens, two associated with spicules (arrows to
main body), SAM P44335, Ediacara South.
Figure 3. Reconstruction
of Coronacollina acula
morphology. Three raised
points on rim are evident,
with a central hollow, and
four spicules extending from the cone rim.
Note that a Corona collina specimen could have
more than four spicules,
but this has not been observed in this study.
the Cambrian Fezouata Formation of Morocco,
silicified examples with raised central regions
28 mm in diameter may represent soft tissue
that was replaced with pyrite (Botting, 2007).
In terms of proportions, Coronacollina has a
smaller central disc and fewer, longer radiating structures (spicules) than Choia. Choia
spicules also occur in closer proximity to each
other and, apparently, taper at both ends.
Wang et al. (2010) suggest that Choia rested
on the seafloor, rather than being attached to it.
They concluded that the large Choia spicules
may have acted as stabilizing pillars against
rotation or tumbling. The spicules possessed by
Coronacollina may have served a similar function, or helped anchor the organism in the microbial mat. Biomineralization had evolved by the
latest part of the Ediacaran Period, as evident
in mineralized tubes such as Cloudina (Germs,
1972; Hua et al., 2005; Hofmann and Mountjoy, 2001). Coronacollina spicules are straight,
rigid structures that were most commonly broken once disarticulated. Some spicules display
a slight deviation from ruler-straight, implying
either a composition of chitin that was plastic
during life, or a mineralized composition of
biogenic silica or calcium carbonate preserved
deformed due to plastic behavior postburial as
GEOLOGY, April 2012
described in Harvey (2010). The abundance
of small spicules suggests breakage after disarticulation and supports a mineralized composition of calcium carbonate or biogenic
silica. The actual spicules are not preserved, if
only because biogenic silica, calcium carbonate, or chitin are all materials that are not likely
to be preserved in coarse siliciclastic sediment
(Droser et al., 2006). Spongin fibers resist
decay longer than cellular tissue, but are readily
washed away and degraded by bacterial action
over weeks or months (Rützler and Macintyre,
1978). Opaline silica spicules dissolve rapidly
(Rützler and Macintyre, 1978), and no organic
material is preserved in the Ediacara Member
of the Rawnsley Quartzite. As no evidence of
movement was observed, Coronacollina is
interpreted as a sessile benthic organism. Its
similarity to Choia suggests that it can best be
interpreted as a sponge-grade metazoan.
Although biomarker evidence suggests the
presence of sponges before the late Cryogenian
glaciation at ca. 635 Ma (Love et al., 2009), and
various Ediacaran fossils have been proposed
as putative sponges (Gehling and Rigby, 1996;
Brasier et al., 1997; Li et al., 1998; Clapham
et al., 2004; Serezhnikova and Ivantsov, 2007;
Sperling et al., 2007), Coronacollina solidifies
the Precambrian fossil record of sponges with the
presence of unequivocal macroscopic spicules.
More importantly, this discovery bears on the
issue of the early evolution of hard-part skeletons
and the development of complex morphologies.
The long, straight and very thin impressions in
bed soles simply cannot be attributed to anything
else but rigid materials, such as silica spicules.
Pseudopods, tentacles, and other soft tissues are
never preserved in sharp, negative hyporelief like
these needle-like forms of Coronacollina and
the spicular meshwork of Palaeophragmodictya
reticulata (Gehling and Rigby, 1996), the other
sponge-grade organism described from the Ediacara Member. Coronacollina provides evidence
of skeletal hard parts in the Ediacaran period,
as well as the presence of a Cambrian-type constructional morphology.
CONCLUSIONS
Coronacollina has skeletonized components
and represents both the oldest multielement
and the oldest disarticulating fossil. The occurrence of Coronacollina on fossil-bearing slabs,
collected for other taxa, indicates that it was a
common element of the Ediacara biota in South
Australia, belatedly recognized because of its
common disarticulation that left needle-like
spicules separated from the variably preserved
sponge body. This complex mode of construction is prevalent among Cambrian clades as
well as taxa extant today. While the genus Coronacollina does not itself extend into the Cambrian as far we know now, the discovery of this
fossil does provide a critical link between the
Ediacara biota and the subsequent Cambrian
fauna in terms of constructional morphologies
and is consistent with the idea that the Ediacara
biota represent stem group taxa of extant clades
(Erwin, 2009) rather than a failed experiment
(Seilacher, 1989).
APPENDIX: SYSTEMATIC PALEONTOLOGY
Coronacollina acula gen. et sp. nov.
Etymology
Name based on fossil morphology; corona L. for
rim; collis L. for hill; acula L. for needle.
Type Specimens
Holotype SAM P43257, an external mold exhibiting both fossil components. Paratypes SAM P43378,
SAM P44335, SAM P43375.
Locality and Horizon
Ediacara Member, Rawnsley Quartzite, Flinders
Ranges, South Australia, with holotype from Bathtub
Gorge (Heysen Range). Other type specimens from
Nilpena, and Ediacara Conservation Park. Articulated
specimens found on five separate bedding surfaces in
negative hyporelief.
Diagnosis
Truncated cone 1–22 mm in diameter, 1–15 mm
tall associated with narrow (commonly <1 mm wide)
309
Downloaded from geology.gsapubs.org on June 15, 2012
straight spicules <2 cm to 37 cm in length, with rare
lenticular sections. Multiple spicules (up to four
observed) diverge radially from cone and commonly
disarticulate. Cone thimble-shaped, with threefold rim
(top outer edge) diameter slightly smaller than base
diameter. Periphery of cone base not sharply defined.
In best-preserved examples, cone symmetrical with
circular to polygonal shallow recess at top. Irregular
specimens have similar relief and cone shape but lack
distinct rims. Spicules attach at cone rim. Smaller
specimens have three separate nodes instead of a continuous rim and are not commonly found with associated spicules.
ACKNOWLEDGMENTS
This research was supported by a National Science Foundation grant (EAR-0074021) and a NASA
grant (NNG04GJ42G NASA Exobiology Program)
to M.L.D., a University of California, Riverside,
John Dunham Field Grant to E.C.C., and an Australian Research Council Discovery Grant (DP0453393)
to J.G.G. We are indebted to Jane and Ross Fargher
for access to their property. Fieldwork was facilitated
by D. Rice, M. Dzaugis, M.E. Dzaugis, J. Perry, A.
Sappenfield, D.A. Droser, members of the South Australian Museum Waterhouse Club, and the Ediacaran
Foundation. A. Sappenfield assisted with Figure 1; D.
Garson constructed Figure 3; M.-A. Binnie assisted
with cataloging. Thanks to three anonymous reviewers for their constructive comments.
REFERENCES CITED
Amthor, J.E., Grotzinger, J.P., Schroeder, S., Bowring, S.A., Ramezani, J., Martin, M.W., and
Matter, A., 2003, Extinction of Cloudina and
Namacalathus at the Precambrian-Cambrian
boundary in Oman: Geology, v. 31, p. 431–
434, doi:10.1130/0091-7613(2003)031<0431:
EOCANA>2.0.CO;2.
Botting, J.P., 2007, “Cambrian” demosponges in
the Ordovician of Morocco: Insights into the
early evolutionary history of sponges: Geobios, v. 40, p. 737–748, doi:10.1016/j.geobios
.2007.02.006.
Brasier, M., Green, O., and Shields, G., 1997, Ediacaran sponge spicule clusters from southwestern
Mongolia and the origins of the Cambrian fauna:
Geology, v. 25, p. 303–306, doi:10.1130/0091
-7613(1997)025<0303:ESSCFS>2.3.CO;2.
Clapham, M.E., Narbonne, G.M., Gehling, J.G.,
Greentree, C., and Anderson, M.M., 2004,
Thectardis avalonensis: A new Ediacaran fossil from the Mistaken Point biota, Newfoundland: Journal of Paleontology, v. 78, p. 1031–
1036, doi:10.1666/0022-3360(2004)078<1031:
TAANEF>2.0.CO;2.
Cohen, P.A., and 13 others, 2009, Tubular compression fossils from the Ediacaran Nama Group,
Namibia: Journal of Paleontology, v. 83,
p. 110–122, doi:10.1666/09-040R.1.
Conway Morris, S., 1993, Ediacaran-like fossils in
Cambrian Burgess Shale–type faunas of North
America: Palaeontology, v. 36, p. 593–635.
310
Droser, M.L., Gehling, J.G., and Jensen, S.R., 2006,
Assemblage palaeoecology of the Ediacara
biota: The unabridged edition?: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 232,
p. 131–147, doi:10.1016/j.palaeo.2005.12.015.
Erwin, D.H., 2009, Early origin of the bilaterian
developmental toolkit: Royal Society of London Philosophical Transactions, ser. B, v. 364,
p. 2253–2261, doi:10.1098/rstb.2009.0038.
Gehling, J.G., 1999, Microbial mats in terminal Proterozoic siliciclastics: Ediacaran death masks:
PALAIOS, v.14, p. 40–57, doi:10.2307/3515360.
Gehling, J.G., 2000, Environmental interpretation
and a sequence stratigraphic framework for
the terminal Proterozoic Ediacara Member
within the Rawnsley Quartzite, South Australia: Precambrian Research, v. 100, p. 65–95,
doi:10.1016/S0301-9268(99)00069-8.
Gehling, J.G., and Rigby, J.K., 1996, Long expected
sponges from the Neoproterozoic Ediacara
fauna of South Australia: Journal of Paleontology, v. 70, p. 185–195.
Germs, J.G.B., 1972, New shelly fossils from the
Nama Group, South West Africa: American Journal of Science, v. 272, p. 752–761,
doi:10.2475/ajs.272.8.752.
Hagadorn, J.W., Fedo, C.M., and Waggoner, B.M.,
2000, Early Cambrian Ediacaran-type fossils from California: Journal of Paleontology, v. 74, p. 731–740, doi:10.1666/00223360(2000)074<0731:ECETFF>2.0.CO;2.
Harvey, T.H.P., 2010, Carbonaceous preservation of
Cambrian hexactinellid sponge spicules: Biology Letters, v. 6, p. 834–837, doi:10.1098/
rsbl.2010.0377.
Hofmann, H.J., and Mountjoy, E.W., 2001, Namacalathus-Cloudina assemblage in Neoproterozoic Miette Group (Byng Formation), British
Columbia: Canada’s oldest shelly fossils: Geology, v. 29, p. 1091–1094, doi:10.1130/0091
-7613(2001)029<1091:NCAINM>2.0.CO;2.
Hua, H., Chen, Z., Yuan, X., Zhang, L., and Xiao, S.,
2005, Skeletogenesis and asexual reproduction in
the earliest biomineralizing animal Cloudina: Geology, v. 33, p. 277–280, doi:10.1130/G21198.1.
Jensen, S., Gehling, J.G., and Droser, M.L., 1998,
Ediacara-type fossils in Cambrian sediments:
Nature, v. 393, p. 567–569, doi:10.1038/31215.
Li, C.-W., Chen, J.-Y., and Hua, T.-E., 1998, Precambrian sponges with cellular structures: Science, v. 279, p. 879–882, doi:10.1126/science
.279.5352.879.
Lin, J.-P., Gon, S.M., III, Gehling, J.G., Babcock,
L.E., Zhao, Y.-L., Zhang, X.-L., Hu, S.-X.,
Yuan, J.-L., Yu, M.-Y., and Peng, J., 2006, A
Parvancorina-like arthropod from the Cambrian of South China: Historical Biology, v. 18,
p. 33–45, doi:10.1080/08912960500508689.
Love, G.D., and 12 others, 2009, Fossil steroids record the appearance of Demospongiae during
the Cryogenian period: Nature, v. 457, p. 718–
721, doi:10.1038/nature07673.
Narbonne, G.M., 2005, The Ediacara biota: Neoproterozoic origin of animals and their ecosystem:
Annual Review of Earth and Planetary Sciences, v. 33, p. 421–442, doi:10.1146/annurev.
earth.33.092203.122519.
Rigby, J.K., 1986, Sponges of the Burgess Shale
(Middle Cambrian, British Columbia): Calgary, Alberta, Canadian Society of Petroleum
Geologists, and Toronto, Ontario, Geological
Association of Canada, 105 p.
Rützler, K., and Macintyre, I.G., 1978, Siliceous
sponge spicules in coral reef sediments: Marine Biology, v. 49, p. 147–159, doi:10.1007/
BF00387114.
Sappenfield, A., Droser, M.L., and Gehling, J.G.,
2011, Problematica, trace fossils, and tubes
within the Ediacara Member (South Australia):
Redefining the Ediacaran trace fossil record
one tube at a time: Journal of Paleontology,
v. 85, p. 256–265, doi:10.1666/10-068.1.
Seilacher, A., 1989, Vendozoa: Organismic construction in the Proterozoic biosphere: Lethaia, v. 22,
p. 229–239, doi:10.1111/j.1502-3931.1989.
tb01332.x.
Serezhnikova, E.A., and Ivantsov, A.Y., 2007, Fedomia mikhaili—A new spicule-bearing organism
of sponge grade from the Vendian (Ediacaran)
of the White Sea, Russia: Palaeoworld, v. 16,
p. 319–324, doi:10.1016/j.palwor.2007.07.004.
Sperling, E.A., Pisani, D., and Peterson, K.J., 2007,
Poriferan paraphyly and its implications for
Precambrian palaeobiology, in Vickers-Rich,
P., and Komarower, P., eds., The rise and fall of
the Ediacaran biota: The Geological Society of
London Special Publication 286, p. 355–368.
Tarhan, L.G., Droser, M.L., and Gehling, J.G., 2010,
Taphonomic controls on Ediacaran diversity:
Uncovering the holdfast origin of morphologically variable enigmatic structures: PALAIOS,
v. 25, p. 823–830, doi:10.2110/palo.2010.p10
-074r.
Vickers-Rich, P., and Komarower, P., editors, 2007,
The rise and fall of the Ediacaran biota: The
Geological Society of London Special Publication 286, 456 p.
Waggoner, B., 2003, The Ediacaran biotas in space
and time: Integrative and Comparative Biology,
v. 43, p. 104–113, doi:10.1093/icb/43.1.104.
Wang, X., Hu, S., Gan, L., Wiens, M., and Mueller, W.E.G., 2010, Sponges (Porifera) as living
metazoan witnesses from the Neoproterozoic:
Biomineralization and the concept of their evolutionary success: Terra Nova, v. 22, p. 1–11,
doi:10.1111/j.1365-3121.2009.00909.x.
Xiao, S., and Laflamme, M., 2009, On the eve of animal radiation: Phylogeny, ecology, and evolution of the Ediacara biota: Trends in Ecology
& Evolution, v. 24, p. 31–40, doi:10.1016/j
.tree.2008.07.015.
Manuscript received 14 September 2011
Revised manuscript received 18 October 2011
Manuscript accepted 30 October 2011
Printed in USA
GEOLOGY, April 2012