A Review And Evaluation Of Homology Hypotheses In Echinoderm Paleobiology

The extraxial-axial theory (EAT) and universal elemental homology (UEH) are often portrayed as mutually exclusive hypotheses of homology within pentaradiate Echinodermata. EAT describes homology upon the echinoderm bauplan, interpreted through early post-metamorphic growth and growth zones, dividing it into axial regions generally associated with elements of the ambulacral system and extraxial regions that are not. UEH describes the detailed construction of the axial skeleton, dividing it into homologous plates and plate series based on symmetry, early growth, and function. These hypotheses are not in conflict; the latter is rooted in refinement of the former. Some interpretive differences arise because many of the morphologies described from eleutherozoan development are difficult to reconcile with Paleozoic forms. Conversely, many elements described for Paleozoic taxa by UEH, such as the peristomial border plates, are absent in eleutherozoans. This Element recommends these two hypotheses be used together to generate a better understanding of homology across Echinodermata.

This Element reviews the ecologies of skeletal trace-producing interactions on echinoids in Modern ecosystems and the recognition of those biogenic traces in the fossil record. This title is also available as Open Access on Cambridge Core.

The dominant faunal elements in shallow Paleozoic oceans, echinoderms are important to understanding these marine ecosystems. Echinoderms (which include such animals as sea stars, crinoids or sea lilies, sea urchins, sand dollars, and sea cucumbers) have left a rich and, for science, extremely useful fossil record. For various reasons, they provide the ideal source for answers to the questions that will help us develop a more complete understanding of global environmental and biodiversity changes. This volume highlights the modern study of fossil echinoderms and is organized into five parts: echinoderm paleoecology, functional morphology, and paleoecology; evolutionary paleoecology; morphology for refined phylogenetic studies; innovative applications of data encoded in echinoderms; and information on new crinoid data sets.

The quantification of morphology through time is a vital tool in elucidating macroevolutionary patterns. Studies of disparity require intense effort but can provide insights beyond those gained using other methodologies. Over the last several decades, studies of disparity have proliferated, often using echinoderms as a model organism. Echinoderms have been used to study the methodology of disparity analyses and potential biases as well as documenting the morphological patterns observed in clades through time. Combining morphological studies with phylogenetic analyses or other disparate data sets allows for the testing of detailed and far-reaching evolutionary hypotheses.

Modern videography provides an ever-widening window into subsea echinoderm life with vast potential for new knowledge. Supported by video evidence throughout, this Element begins with time-lapse video made in 1983 on film, using an off-the-shelf camera, flash, and underwater housings. Although quality has now been significantly improved by digital imagery, films from over thirty years ago captured crinoid feeding behavior previously unknown and demonstrated a great potential to learn about many other aspects of their biology. This sequence is followed by several examples of recent digital videography from submersibles of deep-sea crinoids and remotely operated vehicles (ROVs) (stalked and unstalked), as well as close-up video of crinoids in aquaria. These recent studies enabled a new classification of crinoid arm postures, provided detailed views of food particle capture, and revealed a wide range of behaviors in taxa never before seen in life.

“An enjoyable read that provides a substantial amount of detail on the biology, ecology, and distribution of these fantastic animals . . . Highly recommended.” —Choice More than 10,000 years ago spectacularly large mammals roamed the pampas and jungles of South America. This book tells the story of these great beasts during and just after the Pleistocene, the geological epoch marked by the great ice ages. Megafauna describes the history and way of life of these animals, their comings and goings, and what befell them at the beginning of the modern era and the arrival of humans. It places these giants within the context of the other mammals then alive, describing their paleobiology—how they walked; how much they weighed; their diets, behavior, biomechanics; and the interactions among them and with their environment. It also tells the stories of the scientists who contributed to our discovery and knowledge of these transcendent creatures and the environment they inhabited. The episode known as the Great American Biotic Interchange, perhaps the most important of all natural history “experiments,” is also an important theme of the book, tracing the biotic events of both North and South America that led to the fauna and the ecosystems discussed in this book. “Collectively, this book brings attention to the discovery and natural history of ancient beasts in South America while providing a broader temporal and geographic background that allows readers to understand their evolution and potential immigration to South America.” —Quarterly Review of Biology “An excellent volume . . . This book is likely to facilitate progress in the understanding of fossil mammals from the Americas.” —Priscum

Looks at the wildlife of the ancient supercontinent of Gondwana.