Darwin's Dilemma: the Realities of the Cambrian 'explosion'

Overview

Journal Philos Trans R Soc Lond B Biol Sci

Specialty Biology

Date 2006 Jun 7

PMID 16754615

Citations 28

Authors

Simon Conway Morris

Affiliations

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Abstract

The Cambrian 'explosion' is widely regarded as one of the fulcrum points in the history of life, yet its origins and causes remain deeply controversial. New data from the fossil record, especially of Burgess Shale-type Lagerstätten, indicate, however, that the assembly of bodyplans is not only largely a Cambrian phenomenon, but can already be documented in fair detail. This speaks against a much more ancient origin of the metazoans, and current work is doing much to reconcile the apparent discrepancies between the fossil record, including the Ediacaran assemblages of latest Neoproterozoic age and molecular 'clocks'. Hypotheses to explain the Cambrian 'explosion' continue to be generated, but the recurrent confusion of cause and effect suggests that the wrong sort of question is being asked. Here I propose that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.

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References

Magallon S, Sanderson M . Angiosperm divergence times: the effect of genes, codon positions, and time constraints. Evolution. 2005; 59(8):1653-70. DOI: 10.1554/04-565.1. View

Seo H, Edvardsen R, Maeland A, Bjordal M, Jensen M, Hansen A . Hox cluster disintegration with persistent anteroposterior order of expression in Oikopleura dioica. Nature. 2004; 431(7004):67-71. DOI: 10.1038/nature02709. View

Huang D, Chen J, Vannier J, Saiz Salinas J . Early Cambrian sipunculan worms from southwest China. Proc Biol Sci. 2004; 271(1549):1671-6. PMC: 1691784. DOI: 10.1098/rspb.2004.2774. View

Clarke J, Tambussi C, Noriega J, Erickson G, Ketcham R . Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature. 2005; 433(7023):305-8. DOI: 10.1038/nature03150. View

Morris S . Evolution: bringing molecules into the fold. Cell. 2000; 100(1):1-11. DOI: 10.1016/s0092-8674(00)81679-7. View

Narbonne G . Modular construction of early Ediacaran complex life forms. Science. 2004; 305(5687):1141-4. DOI: 10.1126/science.1099727. View

Chen J, Oliveri P, Gao F, Dornbos S, Li C, Bottjer D . Precambrian animal life: probable developmental and adult cnidarian forms from Southwest China. Dev Biol. 2002; 248(1):182-96. DOI: 10.1006/dbio.2002.0714. View

Heckman D, Geiser D, Eidell B, STAUFFER R, Kardos N, Hedges S . Molecular evidence for the early colonization of land by fungi and plants. Science. 2001; 293(5532):1129-33. DOI: 10.1126/science.1061457. View

Rasmussen B, Bengtson S, Fletcher I, McNaughton N . Discoidal impressions and trace-like fossils more than 1200 million years old. Science. 2002; 296(5570):1112-5. DOI: 10.1126/science.1070166. View

10.

Seilacher , Bose , Pfluger . Triploblastic animals more than 1 billion years ago: trace fossil evidence from india . Science. 1998; 282(5386):80-3. DOI: 10.1126/science.282.5386.80. View

11.

Gissi C, Iannelli F, Pesole G . Complete mtDNA of Ciona intestinalis reveals extensive gene rearrangement and the presence of an atp8 and an extra trnM gene in ascidians. J Mol Evol. 2004; 58(4):376-89. DOI: 10.1007/s00239-003-2559-6. View

12.

Bleidorn C, Vogt L, Bartolomaeus T . New insights into polychaete phylogeny (Annelida) inferred from 18S rDNA sequences. Mol Phylogenet Evol. 2003; 29(2):279-88. DOI: 10.1016/s1055-7903(03)00107-6. View

13.

Van Tuinen M, Hadly E . Calibration and error in placental molecular clocks: a conservative approach using the cetartiodactyl fossil record. J Hered. 2004; 95(3):200-8. DOI: 10.1093/jhered/esh045. View

14.

De Rosa R, Grenier J, Andreeva T, Cook C, Adoutte A, Akam M . Hox genes in brachiopods and priapulids and protostome evolution. Nature. 1999; 399(6738):772-6. DOI: 10.1038/21631. View

15.

Roy S, Gilbert W . Resolution of a deep animal divergence by the pattern of intron conservation. Proc Natl Acad Sci U S A. 2005; 102(12):4403-8. PMC: 555513. DOI: 10.1073/pnas.0409891102. View

16.

Smith M, Johanson Z . Separate evolutionary origins of teeth from evidence in fossil jawed vertebrates. Science. 2003; 299(5610):1235-6. DOI: 10.1126/science.1079623. View

17.

Shu D, Conway Morris S, Han J, Zhang Z, Liu J . Ancestral echinoderms from the Chengjiang deposits of China. Nature. 2004; 430(6998):422-8. DOI: 10.1038/nature02648. View

18.

Butterfield N . Exceptional fossil preservation and the cambrian explosion. Integr Comp Biol. 2011; 43(1):166-77. DOI: 10.1093/icb/43.1.166. View

19.

Xiao S, Shen B, Zhou C, Xie G, Yuan X . A uniquely preserved Ediacaran fossil with direct evidence for a quilted bodyplan. Proc Natl Acad Sci U S A. 2005; 102(29):10227-32. PMC: 1177372. DOI: 10.1073/pnas.0502176102. View

20.

Dong X, Donoghue P, Cheng H, Liu J . Fossil embryos from the Middle and Late Cambrian period of Hunan, south China. Nature. 2004; 427(6971):237-40. DOI: 10.1038/nature02215. View