2012 Annual Science Report
Massachusetts Institute of Technology Reporting | SEP 2011 – AUG 2012
Ediacaran-Cambrian Diversification of Animals
We have continued our focus on the record of the early origin of animals, focusing on the fossil record of the Ediacaran and Early Cambrian. Our comprehensive analysis of the Ediacaran-Cambrian diversification of animals, using a new database of first occurrences combined with new molecular clock results (in collaboration with Peterson’s group), was published last year in Science. Erwin and Valentine completed the first comprehensive book on the Cambrian explosion, which is in press and due for release in late 2012 or early 2013.
Team member Doug Erwin, post-doc Marc Laflamme, and graduate student Sarah Tweedt, continued work on the diversification of animals during the Ediacaran and Cambrian. This work built upon a Research Article, published in Science in late 2011 (and in press for the 2011 NAI Annual Report), which combined a new compilation of the fossil record of this interval with a new molecular clock analysis (conducted by Team Member Kevin Peterson, and colleagues) as well as an analysis of the environmental, ecological and developmental aspects of the Cambrian Radiation. Erwin completed the first comprehensive, book-length treatment of the Cambrian radiation, with Jim Valentine (UC Berkeley). Profusely illustrated, this 450 pg book discusses the geological setting, metazoan phylogeny, the pattern of fossil diversification during the Ediacaran and Cambrian, and the paleoecological and developmental aspects of this event, before presenting a new perspective on its complex causality. Generation of figures and art, editing and proofing of the book has been completed and it is now at the printer, with publication expected in early 2013. Sarah Tweedt has been focusing on her dissertation; this will involve several components, focusing on constructing developmental morphospaces of Ediacaran macrofossils, and of Cambrian panarthropods. Rather than debating the phylogenetic affinities of the Ediacaran forms, Tweedt is developing an approach to understanding the developmental tools required to generate these fossils, an approach with obvious applicability to remote analysis of complex life.
Our group also focused this year on an analysis of a putative end-Ediacaran mass extinction event, which has been discussed for many years. A comprehensive database of first and last occurrences and biogeographic distributions of all Ediacaran species, combined with paleoecological evaluations of diverse Ediacaran communities, was compiled by NAI funded postdoctoral fellow Marc Laflamme. Our study does not support an environmentally-driven mass extinction akin to the Phanerozoic “big five mass extinctions”, but instead supports a drastic ecosystem restructuring across the Ediacaran-Cambrian boundary driven by metazoan ecosystem engineers. This paper was invited and is presently in review at Gondwana Research.