Starfish (or sea stars) are among the most distinctive animals encountered on the seashore today. Together with other easily recognizable forms such as brittle stars, sea cucumbers, sea lilies, and sea urchins, they belong to a major group of invertebrates called the echinoderms. Echinoderms are well represented in modern marine environments, with around 7000 living species, and the group is also characterized by a rich fossil record, which dates back over half a billion years. As a result, studying the fossil record of echinoderms can provide valuable insights into the history and evolution of this important animal group.

A new special issue of the Journal of Paleontology, published on 12th June 2017, brings together a collection of 17 papers focused on different aspects of echinoderm paleobiology. The issue is the result of a meeting in Zaragoza, Spain, held in June 2015, where about 50 scientists interested in echinoderms gathered together to celebrate the career of Dr. Andrew Smith, a world-renowned specialist in echinoderms who retired in late 2012. The papers included in this issue showcase the latest research on fossil echinoderms, with contributions covering a broad range of topics.

Papers by Paul and Sumrall tackle the contentious question of how to determine if parts of the skeleton in different echinoderm groups are derived from the same ancestral structure (i.e. homology). Next, a study by Deline and Thomka explores how variation in how well fossils are preserved can influence attempts to characterize differences in the form and structure of different species.

Grun et al. present new information on how frequently a species of fossil sea urchin was damaged by predatory snails. Belaústegui et al. review the record of burrows and borings produced by echinoderms, as well as the traces left by other organisms on echinoderms.

Waters et al. make use of a method more commonly used in engineering, computational fluid dynamics, to study how the inner structures of a fossil echinoderm direct water flow.

Following this are seven papers focused on detailed descriptions of fossil echinoderms. Nardin et al. describe a new genus of primitive echinoderm from the Cambrian of the Czech Republic. Allaire et al. revise the genus Rhopalocystis from the Ordovician of Morocco. Cole et al. describe several new crinoids from the Ordovician of Spain. Reich et al. report the first cyclocystoid from the Ordovician of Morocco. Sheffield and Sumrall revise the puzzling Holocystites fauna from the Silurian of midcontinental North America. Thompson et al. describe new sea urchins from the Permian of Texas. Lastly, Ewin and Thuy describe three new species of brittle star from the Jurassic of the United Kingdom.

The special issue ends with four papers dealing with the evolutionary relationships of fossil echinoderms. Wright, Cole, and Wright et al. present analyses of the relationships of different crinoids, while Bauer et al. explore the relationships of the extinct blastoids.

Dr. Andrew Smith, to whom the special issue is dedicated, said: “Echinoderms, with their complex multiplated skeleton and often excellent fossil record, provide a wonderful group with which to explore evolutionary patterns and processes over deep time. While the living fauna allows detailed understanding of the links between form and function to be established, early fossil representatives still pose a major challenge to palaeontologists, as the group has undergone some radical shifts in body plan and lifestyle.  This set of papers highlights how the study of fossil echinoderms continues to surprise, as new discoveries and new insights progress our understanding of their rich and varied history”. Dr. Jisuo Jin, editor of the Journal of Paleontology, added: “In many ways, echinoderm research is leading the field of paleontological research, from sophisticated morphometric analysis to cutting-edge systematics that combines quantitative techniques with evolutionary hypotheses to extend far beyond the traditional Linnaean classification system. These leading-edge research directions are well reflected in the excellent papers of this special issue”.

Written by Guest Editors: Samuel Zamora and Imran A. Rahman

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