Sunday, 6 December 2015

Animal evolution: Sponges really are oldest animal phylum


Date:December 1, 2015
Source:Ludwig-Maximilians-Universitaet Muenchen (LMU)

Who came first -- sponges or comb jellies? A new study by an team of Ludwig-Maximilians-Universitaet (LMU) in Munich reaffirms that sponges are the oldest animal phylum -- and restores the classical view of early animal evolution, which recent molecular analyses had challenged.

The answer to the question of whether the sponges or the comb jellies (also known as sea gooseberries) represent the oldest extant animal phylum is of crucial importance to our understanding of organismic evolution. The two possible solutions have very different consequences for our understanding of central aspects of the early evolution of multicellular animals (Metazoa), such as the origins of nervous systems, tissues and organs. In recent years, new data have once again brought this issue into focus and given rise to controversial debates among zoologists. Now, a re-analysis of the evidence by an international group of evolutionary biologists has convincingly refuted the proposition that comb jellies are the phylogenetically oldest extant metazoan group. The new study, a collaborative effort by groups led by Professor Gert Wörheide (Chair of Paleontology and Geobiology at LMU) and Dr. Davide Pisani (Bristol University, UK) reaffirms the traditional view that the sponges were the first phylum to diverge from the common ancestor of metazoans. "Some recent studies seemed to imply that comb jellies were the trendsetters in animal evolution. But we were able to disprove this idea by using more powerful and sophisticated methods to analyze the genetic data presented in those studies," says Wörheide. The new results appear in the journal Proceedings of the National Academy of Sciences (PNAS).

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