Geological Magazine; January 2008; v. 145; no. 1;
p. 155-156; DOI: 10.1017/S0016756807004116
© 2008 Cambridge University Press (CUP)
BARRAS, C. G. 2006. British Jurassic Irregular Echinoids.
Palaeontographical Society Monographs 159 (no. 625). 273 pp. + 14 plates. London: The Palaeontographical Society. Price £130 plus p+p (paperback). ISSN 0269-3445.
Rich Mooi
Recently there has been an upsurge in interest in sea urchin evolution, inspired in part by the acquisition in 2006 of a complete echinoid DNA sequence, use of echinoids as model organisms in a variety of contexts, their important roles as keystone consumers in several ecological realms, and events that lead to major embryological changes not only in developmental modes but in axes of symmetry. The evolutionary history of the group is therefore of extreme importance, and Barras has provided a fine glimpse into a major component thereof. He considers the systematics of more than 30 critical Jurassic species, provides many luscious drawings and photos for these forms, develops well-explicated keys to their identification, sets the taxa in a stratigraphic context, clarifies many nomenclatural problems, and then analyses phylogenetic relationships. As a reference work on British Jurassic echinoids, the book is unparalleled in its breadth of coverage and detail. There are fine drawings and descriptions of overall morphology to help the novice, and plenty of information for specialists as well. For me, the photos on page 32 showing the spines, pedicellariae, and even a sphaeridium otherwise so rarely preserved in fossil urchins (never mind those from the Mesozoic) are almost worth the price of admission alone. There are also numerous plots of various anatomical features that provide a glimpse into the carefully collected mensural data that are required to distinguish species.
I remain somewhat leery of geographically constrained phylogenetic analyses because the omission of non-British forms could potentially alter views on homologies and relationships among the characters and taxa. In fact, a recent work uncited by Barras, likely because it was developed virtually in parallel with the book (Saucède, Mooi & David, 2007), takes a somewhat more global approach and arrives at slightly different phylogenetic conclusions. I suggest, for example, the placement of Hyboclypus. The characters that push this form into the atelostomates are not entirely convincing and the low bootstrap values for this part of the phylogeny are no surprise. A look at some of the characters that link this important Jurassic echinoid to more crownward groups in the atelostomates is especially telling as every one of them is homoplastic, with one supporting at least four other rather disparate nodes.
In spite of some remarkably similar major findings between the two studies, it is clear that there is still some room for discussion about the origins of bilateral symmetry within the Echinoidea, and a truly definitive work that includes all the major clades of the Irregularia, including post-Jurassic ones, is a logical next step in resolving important, outstanding issues. Apart from being a lavish introduction to British species, in the context of ongoing research, Barras’ book will best be used in conjunction with other works dealing with the precise placement of taxa integral to our understanding of the evolutionary history of the Irregularia – a history that is clearly rooted in the Jurassic.
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SAUCEDE, T., MOOI, R. & DAVID, B. 2007. Phylogeny and origin of Jurassic irregular echonoids (Echinodermata: Echinoidea). Geological Magazine 144, 333–59.[Abstract/Free Full Text][CrossRef][Web of Science][GeoRef]
Copyright © 2009 by Cambridge University Press (CUP)
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