A critical reappraisal of the fossil record of the bilaterian phyla

  title={A critical reappraisal of the fossil record of the bilaterian phyla},
  author={Graham E. Budd and S{\"o}ren Jensen},
  journal={Biological Reviews},
It has long been assumed that the extant bilaterian phyla generally have their origin in the Cambrian explosion, when they appear in an essentially modern form. Both these assumptions are questionable. A strict application of stem‐ and crown‐group concepts to phyla shows that although the branching points of many clades may have occurred in the Early Cambrian or before, the appearance of the modern body plans was in most cases later: very few bilaterian phyla sensu stricto have demonstrable… 

Ecological innovations in the Cambrian and the origins of the crown group phyla

  • G. BuddI. Jackson
  • Geography, Environmental Science
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2016
It is suggested that the vagrant lifestyle of annelids, nemerteans and molluscs would be independently derived from such a sessile ancestor, with potentially important implications for the homology of their sensory and nervous systems.

The origin of the animals and a ‘Savannah’ hypothesis for early bilaterian evolution

  • G. BuddS. Jensen
  • Environmental Science, Geography
    Biological reviews of the Cambridge Philosophical Society
  • 2017
The subtle remnants of Ediacara‐style taxa within the Cambrian suggest that they remained significant components of Phanerozoic communities, even though at some point their enabling role for bilaterian evolution was presumably taken over by bilaterians or other metazoans.

The origin of annelids

A novel clade of machaeridians, the Cuniculepadida, is identified, which exhibit a series of adaptations for burrowing, and is identified as a convincing body of molecular evidence that polychaetes form a paraphyletic grade and that clitellates are derived polychaETes.

The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records

The two historical records of life both suggest that although the cradle of Metazoa lies in the Cryogenian, and despite the explosion of ecology that occurs in the Cambrian, it is the emergence of bilaterian taxa in the Ediacaran that sets the tempo and mode of macroevolution for the remainder of geological time.

Morphological and developmental macroevolution: a paleontological perspective.

Study of genomic differences among crown classes and orders whosetiming and mode of origin can be inferred from morphological data inthefossil record should throw further light on the timing and mode-of- origin of genomic disparities.

The earliest fossil record of the animals and its significance

  • G. Budd
  • Geography, Environmental Science
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2008
A reasonable case can now be made for the extension of the fossil record of at least basal animals (sponges and perhaps cnidarians) to a period of time significantly before the beginning of the Cambrian.

The Precambrian emergence of animal life: a geobiological perspective

It is proposed that the recorded Precambrian evolution of animals includes three intervals of advancement that begin with sponge-grade organisms, and that any preceding cryptic fauna would be no more complex than sponges.

The origin of animals: Can molecular clocks and the fossil record be reconciled?

Despite challenges provided by incomplete preservation, a paucity of phylogenetically informative characters, and uncertain expectations of the anatomy of early animals, a number of Neoproterozoic fossils can reasonably be interpreted as metazoans.

Exceptionally preserved crustaceans from western Canada reveal a cryptic Cambrian radiation

Diverse crustacean appendages of Middle and Late Cambrian age from shallow-marine mudstones of the Deadwood Formation in western Canada provide the earliest evidence for crown-group branchiopods and total-group copepods and ostracods, extending the respective ranges of these clades back from the Devonian, Pennsylvanian, and Ordovician.



Late Precambrian bilaterians: grades and clades.

  • J. W. Valentine
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1994
Evidence from the fossil record can be combined with that from molecular phylogenetic trees to suggest that the last common ancestor of (i) protostomes and deuterostomes was a roundish worm with a blood vascular system and (ii) of arthropods and annelids was similar, with a hydrostatic hemocoel, among trace makers of the late Precambrian.

The Cambrian evolutionary ‘explosion’: decoupling cladogenesis from morphological disparity

Evidence is presented that the important events in the generation of clades were earlier than the Cambrian ‘explosion’, at which time the groups become manifest in the fossil record.


A model of ecospace occupation involving evolutionary preclusion and access appears to be consistent with the data as now understood, and the genome hypothesis is unlikely to explain the restriction on evolutionary novelty.


  • M. Lynch
  • Biology
    Evolution; international journal of organic evolution
  • 1999
The results of this study suggest that, with appropriate levels of taxon sampling and a focus on conserved regions of protein‐coding sequence, complete mitochondrial genome analysis may be sufficiently powerful to elucidate the genealogical relationships of many of the animal phyla.

Lower Cambrian vertebrates from south China

The discovery of two distinct types of agnathan from the Lower Cambrian Chengjiang fossil-Lagerstätte imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, ∼555 Myr BP), if not earlier.

Eggs and embryos from the Cambrian.

  • S. Morris
  • Environmental Science
    BioEssays : news and reviews in molecular, cellular and developmental biology
  • 1998
A surprising new discovery of eggs with blastomeres and embryos with well-defined anatomy from the Cambrian of China and Siberia promises to extend the arena of debate on the nature of the earliest animals and when they originated.

The Origin of Bodyplans

The nested hierarchical structure of developmental control genes and bodyplan originations suggests certain temporal inhomogeneities to the evolutionary process: as certain developmental patterns are established they limit subsequent evolutionary trajectories.

Testing the Darwinian legacy of the Cambrian radiation using trilobite phylogeny and biogeography

Although the tempo of evolution during the Cambrian radiation may not have been uniquely high, there were largely unique tectonic events that transpired during the late Neoproterozoic and Early Cambrian, such as extensive cratonic fragmentation.

Origin of the metazoan phyla: molecular clocks confirm paleontological estimates.

This work has analyzed 18 protein-coding gene loci and estimated that protostomes (arthropods, annelids, and mollusks) diverged from deuterostomes about 670 million years ago, and chordates from echinoderms about 600 million years old, consistent with paleontological estimates.

The monophyletic origin of the Brachiopoda

Cladistic analysis of both living forms and Lower Paleozoic taxa strongly supports the contention that brachiopods are monophytetic and closely related to the phoronids and suggests, however, that the ‘inarticulate’ Paterinida and Kutorginida are genealogically more closely related than they are to the remaining Inarticulata.