Abstract
The origin and differentiation of major clades is often assumed to have occurred in tandem with the 'explosion' of fossil evidence of diverse morphologies ('disparity') at the base of the Cambrian. Evidence is presented that this was not the case. Biogeographical and morphological differentiation among the earliest trilobites reveals incompleteness in the known early Cambrian record; similar evidence can be accrued for other major groups. Phylogenetic analysis proves the likelihood of 'ghost' lineages extending into the Precambrian. 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. It is likely that the important phylogenetic changes happened in animals of small size; sister taxa of major groups are shown to be small animals. Decoupling cladogenesis from the Cambrian 'explosion' removes the necessity of invoking unknown evolutionary mechanisms at the base of the Phanerozoic. Genes controlling development may have played a role in generating new morphologies, through heterochrony for example, in the early differentiation of metazoan body plans.
| Original language | English |
|---|---|
| Pages (from-to) | 13-33 |
| Number of pages | 21 |
| Journal | Biological Journal of the Linnean Society |
| Volume | 57 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 1996 |
Bibliographical note
Funding Information:We thank Andrew B. Smith, Douglas Erwin, Geoffrey Levinton, Colin Patterson and an anonymous referee for reading and suggesting improvements to the manuscript. Jan Bergström and Richard J. Jenkins provided photographs. We thank Mike Foote, Michael Akam, Adrian Friday and Richard Jenkins for discussion. MAW was funded by a University of Bristol postgraduate scholarship. DEGB’s contribution was written while he was a Distinguished Visiting Scholar at the University of Adelaide.
Funding
We thank Andrew B. Smith, Douglas Erwin, Geoffrey Levinton, Colin Patterson and an anonymous referee for reading and suggesting improvements to the manuscript. Jan Bergström and Richard J. Jenkins provided photographs. We thank Mike Foote, Michael Akam, Adrian Friday and Richard Jenkins for discussion. MAW was funded by a University of Bristol postgraduate scholarship. DEGB’s contribution was written while he was a Distinguished Visiting Scholar at the University of Adelaide.
Keywords
- Adaptive radiation
- Basal Cambrian
- Cladistics
- Ghost ranges
- Metazoan phylogeny
- Vendozoa
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics