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Perspectives in Animal Phylogeny and Evolution$
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Alessandro Minelli

Print publication date: 2008

Print ISBN-13: 9780198566205

Published to Oxford Scholarship Online: May 2009

DOI: 10.1093/acprof:oso/9780198566205.001.0001

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Metazoans enter the stage

Metazoans enter the stage

(p.19) Chapter 3 Metazoans enter the stage
Perspectives in Animal Phylogeny and Evolution

Alessandro Minelli

Oxford University Press

Molecular phylogenetics places the animals firmly within the clade of the Opisthokonta, with the choanoflagellates as their most likely sister group. Choanoflagellates possess many of those cell-adhesion and cell-cell signalling molecules that are required for multicellularity. These molecules thus largely predate the evolutionary transition from single cells to multicellular organisms. Palaeontological evidence of the earliest stages of metazoan evolution is either lacking or problematic. Late Precambrian fossils include a diversity of macroscopic forms (often known as the vendobionts) whose phylogenetic relationships to modern metazoans are disputed, and a number of recently described embryos from the Chinese Doushantuo deposits, probably corresponding to adults organisms of minute size. Fossil evidence still supports the concept of a quite sudden Cambrian explosion of animal diversity. Molecular estimates of the timing of divergence of the main metazoan lineages mostly point to ages quite than the base of the Cambrian, but those results are not consistent overall.

Keywords:   Cambrian explosion, choanoflagellates, Doushantuo embryos, Late Precambrian fossils, multicellularity, vendobionts

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