Hidden fossils go on the record

Fossil Crinoids
January 5, 2001

Among fossil organisms, dinosaurs, early humans and other vertebrates continue to have the highest media profile, but ancient invertebrates also have a devoted public following, as indicated by the success of such books as Richard Fortey's Trilobite! and Stephen Jay Gould's Wonderful Life . These volumes were largely devoted to arthropods and other segmented things, but there is more to lacking a backbone than having multiple pairs of jointed legs.

There are no more beautiful living or fossil organisms than the crinoids, a group of animals of plant-like grace closely related to starfishes and sea urchins. However, unlike these related vagile, benthic groups, with mouths directed downwards in search of food, the crinoids are like an inverted starfish, feeding on plankton with their mouths directed away from the sea floor. The arms are commonly branched many times over, producing an efficient net for capturing plankton.

In all probability you will never see a live crinoid in a zoo or aquarium, because they live cryptically or in habitats difficult to reproduce for public displays, particularly deep water. If you really want to see living crinoids, scuba or a research submersible are the best options. An easier possibility is to examine the fossil representatives while treading the galleries of your local natural history museum. Easier still, with the advent of Fossil Crinoids , you can admire their beauty in the comfort of your own home. Hans Hess and his co-authors have written a gem of a book that is beautifully illustrated. It succeeds in bringing the fascination of this ancient group of organisms alive for the reader - professional, student and amateur.

It might be argued that most animal groups alive today are better known from direct observation than from their fossil record. Not so the crinoids, which during the Palaeozoic (between about 500 and 250 million years ago) were present in such numbers in marine environments that their remains formed major rock units. Such regional encrinites, each containing millions of crinoid fragments, may be metres thick and cover hundreds of square kilometres.

Fossil Crinoids is divided into two unequal parts. Five introductory chapters discuss general palaeobiological issues and other matters particularly applicable to crinoids, including where to find the best specimens. This section demonstrates the bias of this volume towards examples from North America and Europe. However, this comment is not a criticism because this geographic selectivity is a good demonstration of what is best known (and, perhaps, where the main market for this book is). It is true that other notable faunas are covered, such as the Permian crinoids of Timor, but such examples are rare.

The remaining 20-plus chapters consider the stratigraphic and spatial distribution of crinoids during the past 500 million years. It is the chapters on fossil assemblages that form the core of the book, examining the history of the crinoids by reference to those assemblages that show exceptional preservation and diversity. This approach, using a series of "focused snapshots", is original and works exceedingly well, resting on those assemblages that provide the maximum palaeobiological information.

Living crinoids are a hot topic and the authors ably apply modern insights on crinoid ecology to the fossil record. Because of the difficulties hitherto experienced in studying the deep water stalked sea lilies, such an authoritative book could only have been published now. The advent of the research submersible led to a revolution in ideas on the ecology of these sea lilies, which hitherto were known only from dredged samples and the fossil record.

In 1974, Bradford Macurda and David Meyer published the first direct observations of extant sea lilies and demonstrated that they are current-loving rheophiles, turning on its head the traditional view of palaeontologists and zoologists that they were current-hating rheophobes. Since then, direct and laboratory observations and experiments have determined that sea lilies show other adaptations and abilities that were similarly unexpected. Thus, it is now recognised that isocrinids, the most commonly studied group, can relocate by walking on their arms and are able to regenerate the crown following autotomy (self-mutilation). An appreciation of such new insights informs the authors' discussions of ancient crinoids.

One problem of the crinoid skeleton is that it is composed of multiple elements of various shapes, called ossicles, analogous to the skeleton of a vertebrate. Hess et al rightly concentrate on complete specimens of the type that grace museum (and notable private) collections, yet the overwhelming majority of crinoid fossils are ossicles.

By concentrating on the rarer, complete end of a preservational spectrum, this volume might prove to be of limited use as an identification guide. However, such selectivity is desirable, as this book is not intended as a treatise on fossil crinoids, but as an introduction to their variety and palaeobiology from the vantage point of some of the best fossil sites in the world.

Stephen K. Donovan is keeper of palaeontology, Natural History Museum, London.

Fossil Crinoids

Author - Hans Hess, William I. Ausich, Carlton E. Brett and Michael J. Simms
ISBN - 0 521 45024 1
Publisher - Cambridge University Press
Price - £47.50
Pages - 5

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