Working Paper Article Version 1 This version is not peer-reviewed

Cambrian Chordates and Vetulicolians

Version 1 : Received: 27 June 2019 / Approved: 3 July 2019 / Online: 3 July 2019 (11:01:11 CEST)

How to cite: McMenamin, M. Cambrian Chordates and Vetulicolians. Preprints 2019, 2019070063 McMenamin, M. Cambrian Chordates and Vetulicolians. Preprints 2019, 2019070063

Abstract

Deuterostomes make a sudden appearance in the fossil record during the Early Cambrian. Two deuterostome groups, the chordates and the vetulicolians, are of particular interest for understanding the evolutionary dynamics of the Cambrian evolutionary event. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document an explosive radiation of deuterostomes at the base of the Cambrian. A new vetulicolian (••• nov. gen. nov. sp.) with a polygonal anterior section and a narrow, unsegmented posterior region (‘tail’) bearing possible myotomes provides new insight into the affinities of the various body plans that emerged during the Early Cambrian. It seems clear that the advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections.

Subject Areas

chordates; vetulicolians; cephalochordates; vertebrates; tunicates; Cambrian; Chenjiang Biota; Burgess Shale; Banffia; Vetulicolia; Myllokunmingia; Metaspriggina; agnathans; deuterostomes; all-trans-retinoic acid (ATRA); morphogen gradients

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