Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian

@article{Chen2004SmallBF,
  title={Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian},
  author={Jun‐yuan Chen and David J. Bottjer and Paola Oliveri and Stephen Q. Dornbos and F. Gao and Seth Ruffins and Huimei Chi and CHIA-WEI Li and Eric H. Davidson},
  journal={Science},
  year={2004},
  volume={305},
  pages={218 - 222}
}
Ten phosphatized specimens of a small (<180 micrometers) animal displaying clear bilaterian features have been recovered from the Doushantuo Formation, China, dating from 40 to 55 million years before the Cambrian. Seen in sections, this animal (Vernanimalcula guizhouena gen. et sp. nov.) had paired coeloms extending the length of the gut; paired external pits that could be sense organs; bilateral, anterior-posterior organization; a ventrally directed anterior mouth with thick walled pharynx… 

Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian"

Coelomate bilaterians from the ∼600-million-year-old Doushantuo phosphorites in southern China might meet some common expectations of small, simple bilaterian emerging after the worldwide glaciations of the Neoproterozoic.

Tiny Sea Anemone from the Lower Cambrian of China

The features found in the present fossils fall within the morphological spectrum of modern Hexacorallia excluding Ceriantharia, and thus Eolympia pediculata could be a stem member for this group.

The rise of bilaterians: a few closing comments

Although Vernanimalcula is a fossil, the purported germ layers of Vern animalcula are of diagenetic origin and there is no morphological evidence in support of its bilaterian affinity, so it is inappropriate to analyse Ediacara fossils using “promorphologies” of extant animals.

Phanerozoic evolution—Ediacaran biota

Complex embryos displaying bilaterian characters from Precambrian Doushantuo phosphate deposits, Weng'an, Guizhou, China

These embryos provide further evidence for the presence of bilaterian animals in the Doushantuo biota and indicate that the last common ancestor of the bilaterians lived much earlier than is usually thought.

Critical appraisal of tubular putative eumetazoans from the Ediacaran Weng'an Doushantuo biota

New insights are presented into the anatomy, original composition and phylogenetic affinities of these taxa based on data from synchrotron radiation X-ray tomographic microscopy, ptychographic nanotomography, scanning electron microscopy and electron probe microanalysis.

The rise of bilaterians

While genera with both kinds of symmetry properties and unitary and colonial animals were present during the early Ediacaran, there was a large proportional increase in new bilaterian genera and a decrease in colonial genera beginning between 560–550 MA.

The Cambrian Conundrum: Early Divergence and Later Ecological Success in the Early History of Animals

A compilation of the patterns of fossil and molecular diversification, comparative developmental data, and information on ecological feeding strategies indicate that the major animal clades diverged many tens of millions of years before their first appearance in the fossil record.

Response to Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian"

It is counterfactual to deny preservation of structural morphology at the cellular level in this kind of material.
...

References

SHOWING 1-10 OF 19 REFERENCES

The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism

This work reconstructs Kimberella as a bilaterally symmetrical, benthic animal with a non-mineralized, univalved shell, resembling a mollusc in many respects, important evidence for the existence of large triploblastic metazoans in the Precambrian and indicates that the origin of the higher groups of protostomes lies well back in the precambrian.

Precambrian animal life: probable developmental and adult cnidarian forms from Southwest China.

The new observations reported in this paper indicate the existence of a diverse and already differentiated cnidarian fauna, long before the Cambrian evolutionary event.

Precambrian animal diversity: putative phosphatized embryos from the Doushantuo Formation of China.

Putative fossil embryos and larvae from the Precambrian phosphorite rocks of the Doushantuo Formation in Southwest China have been examined in thin section and identified what appear to be modern cnidarian developmental stages, including both anthozoan planula larvae and hydrozoan embryos.

Eumetazoan fossils in terminal proterozoic phosphorites?

  • S. XiaoX. YuanA. Knoll
  • Geography, Environmental Science
    Proceedings of the National Academy of Sciences of the United States of America
  • 2000
Evidence for Doushantuo eumetazoans is provided by millimeter-scale tubes that display tabulation and apical budding characteristic of some Cnidaria, especially the extinct tabulates.

Age of Neoproterozoic bilatarian body and trace fossils, White Sea, Russia: implications for metazoan evolution.

A uranium-lead zircon age for a volcanic ash interstratified with fossil-bearing, shallow marine siliciclastic rocks in the Zimnie Gory section of the White Sea region indicates that a diverse assemblage of body and trace fossils occurred before 555.3 +/- 0.3 million years ago, making co-occurring trace fossils the oldest that are reliably dated.

Acoel flatworms: earliest extant bilaterian Metazoans, not members of Platyhelminthes.

Sequence data of 18S ribosomal DNA genes from non-fast evolving species of acoels and other metazoans reveal that this group does not belong to the Platyhelminthes but represents the extant members of the earliest divergent Bilateria, an interpretation that is supported by recent studies on the embryonic cleavage pattern and nervous system of acOels.

PHOSPHATIZED ANIMAL EMBRYOS FROM THE NEOPROTEROZOIC DOUSHANTUO FORMATION AT WENG'AN, GUIZHOU, SOUTH CHINA

Phosphorites of the uppermost Neoproterozoic Doushantuo Formation exposed at Weng'an, South China, contain globular microfossils characterized by distinctively sculpted outer coverings and precise patterns of cell division, which support their reinterpretation as the eggs and embryos of early animals.

The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes

The results imply that the last common ancestor of bilaterian metazoans was a small, benthic, direct developer without segments, coelomic cavities, nephrida or a true brain.

Estimating metazoan divergence times with a molecular clock.

The last common ancestor of bilaterians arose somewhere between 573 and 656 Ma, depending on the value assigned to the parameter scaling molecular substitution rate heterogeneity, and this results support the view that the Cambrian explosion reflects, in part, the diversification of bilateralian phyla.