The internal morphology of primary spines of extant regular echinoids in the tropical western Atlantic: a SEM atlas
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REGULAR RESEARCH ARTICLE
The internal morphology of primary spines of extant regular echinoids in the tropical western Atlantic: a SEM atlas Stephen K. Donovan1 Received: 19 March 2018 / Accepted: 5 July 2018 Ó Akademie der Naturwissenschaften Schweiz (SCNAT) 2018
Abstract The spines of echinoids are common palaeontological objects, but rarely supply more than this minimal information, because they are difficult to identify to genus or species. Some taxa, particularly cidaroids, may be named based on the external morphology of their spines, but this is of no assistance when identifying spines in thin section. Yet, the internal complexities of the stereom of the echinoid spine may be unique to a particular species or, at least, genus or family. A scanning electron micrograph (SEM) atlas of the internal structure of the primary spines of 14 of the most common species of regular echinoids from shallow–water environments of the tropical western Atlantic Ocean is presented herein. This demonstrates the stereom structure of the spines of each of these species by reference to multiple images. Plates of SEMs are supplemented by brief descriptions and comparisons. This atlas is intended as a tool that can be applied to diverse aspects of palaeontological and sedimentological studies in thin section. Keywords Palaeoecology Pliocene Pleistocene Preservation Completeness of the fossil record
Introduction The Palaeontological Association Newsletter publishes a regular series of images of ‘mystery fossils’ that have previously defied the best attempts of researchers to identify them; the readership are invited to do better. The only mystery fossil to attract a reply from me, which was several years ago, was a thin section through a Neogene (Pleistocene?), shallow-water limestone which had sliced through a primary spine of a diadematoid echinoid. I sent my identification to the ‘mystery fossils’ editor and was, by reply, informed that I was wrong and that the specimen had already been identified as a holothurian ossicle. I knew that this was erroneous, yet despite my qualifications to identify an echinoid spine in thin section, the editor of ‘mystery fossils’ was adamant—it was holothurian, not echinoid. I then suggested that a leading expert on extant echinoids
Editorial Handling: D. Marty. & Stephen K. Donovan [email protected] 1
Taxonomy and Systematics Group, Naturalis Biodiversity Center, Postbus 9517, 2300 RA Leiden, The Netherlands
and holothurians might be approached as a neutral referee; he agreed that it was an echinoid. This story demonstrates that even an experienced geologist can have trouble identifying a section through one of the commonest of fossil echinoderm fragments in thin section, that is, an echinoid spine. The present contribution aims to help correct this aberration, at least in part, by providing an atlas of some of the commoner echinoid spines that might be found in shallow-water limestones in the region that I know best, that is, in
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