Biology and Evolution of Crocodylians
Article number: 19.2.2R
August 2016
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Gordon Grigg and David Kirshner, 2015, Comstock Publishing Associates. 672 pages, ISBN: 0801454107
$149.95 (hardcover)
As a paleontologist, I see two primary goals that Gordon Grigg and David Kirshner’s Biology and Evolution of Crocodylians must achieve for readers. It must serve crocodylian biologists by accurately reflecting and summarizing our current understanding of the evolutionary history of Crocodylia and their fossil relatives. Secondly, the book should serve paleontologists as an exhaustive summation of crocodylian anatomy, physiology, life history, ecology, and conservation. I am happy to say that the authors accomplish both goals, making the book an extremely useful resource for anyone interested in this charismatic group of reptiles.
The evolutionary history of Crocodylia is detailed in Chapter 2, entitled “The Crocodylian Family Tree.” This section follows the evolutionary history of the group back to the origin of Diapsida, through the early diversification of Archosauria and Pseudosuchia within the Triassic, the Jurassic and Cretaceous diversification of multiple lineages of Crocodylomorpha, and the surprisingly complex evolution of Crocodylia during the Cenozoic. For each of the major groups in the early Mesozoic (e.g., “sphenosuchians,” “protosuchians”) and later radiations (Thalattosuchia, Notosuchia, Neosuchia), Grigg briefly describes general anatomy and history. He describes one or two exemplar taxa of each broader radiation in detail to illustrate the high diversity in past eras. The research incorporated is up-to-date, and the illustrations capture the history described in the text. This chapter serves as a good and succinct summation of the current knowledge of the fossil history of crocs for non-paleontologists.
Grigg contextualizes the subsequent chapters in evolutionary history. In sections focused on locomotion and metabolism in modern crocodylians, he calls back to the erect posture and cursorial adaptations of early crocodylomorphs. It is refreshing to see the traditionally “reptilian” characters of modern crocodylians considered as apomorphic in a well-founded evolutionary context throughout the text.
The book also succeeds as a summation of knowledge of other aspects of crocodylian biology, and it is one I will refer back to often in the future. In each section, Grigg describes both the current state of knowledge and the historical context for that knowledge, including evolving misconceptions. Chapter 3 is a well-illustrated guide to external and musculoskeletal anatomy.
- Chapter 4 covers locomotion and movement in Crocodylia, with discussions of walking, galloping, diving, and swimming. Extensive attention is given to long-distance travel in Crocodylus porosus.
- Chapter 5 describes the sensory system in Crocodylia, with excellent anatomical illustrations of the eye, brain, and cranial sensory nervous system. Grigg describes the changing knowledge of crocodylian integumentary sense organs in great detail.
- Chapter 6 describes feeding, digestion, and nutrition in Crocodylia. Methods for extracting stomach contents from Crocodylia and the diversity of dietary resources (e.g., fruits, insects) are of particular interest.
- Chapter 7 describes energetics and metabolism. Grigg makes extensive reference to recent discoveries of bird-like lung morphology in Crocodylia and its evolutionary implications. Kirshner provides excellent schematics of the circulatory system in Crocodylus .
- Chapter 8 focuses exclusively on the anatomy and function of the crocodylian heart, which exhibits a unique “cog-wheel valve” at the base of the pulmonary artery. This chapter details numerous hypotheses for the function of this unique circulatory system.
- Chapter 9 explores the mechanics and physiology of diving and submergence. This chapter captures another strength of the book in the large number of graphs and data tables reproduced from past studies, showing the data supporting broader statements about the length, timing, and physiological parameters of dives.
- Chapter 10 describes temperature control in Crocodylia. Extensive attention is given to evolutionary history of endothermy in Archosauria and the hypothesis that Crocodylomorpha are ancestrally endothermic.
- Chapter 11 describes the maintenance of salt and water balance in Crocodylia.
- Chapter 12 covers the reproductive process in Crocodylia, from mating displays and strategies to reproductive physiology to parental care.
- Chapter 13 describes population structure in crocodylian species. This chapter examines a number of large-scale demographic studies of Paleosuchus trigonatus, Crocodylus johnstoni, and Alligator mississippiensis.
- Chapter 14 closes the book with a discussion of the interaction of crocodylians and humans, particularly in terms of conflict, commercialization, and conservation.
The writing style is clear and succinct, and the chapters are broken up with supplemental informational boxes. Grigg opens each chapter with personal anecdotes about his interest in and history with Crocodylia, and some sections are interspersed with his personal research experiences. Many chapters extensively discuss Crocodylus porosus and C. johnstoni to the exclusion of other animals, likely a consequence of Grigg’s extensive background studying Australian species. However, the data referenced throughout the book draw from research on all crocodylian species. Grigg is far from a dispassionate writer, injecting his own enthusiasm for crocodiles throughout the text. Some may find the style and narrative detours overly conversational, but they emphasize the author’s own interests and opinions on open research questions.
All chapters are accompanied with high-quality photographs, illustrating both anatomy and behaviors. The illustrations by David Kirshner throughout the book are an excellent accompaniment to the text, especially in the sections on anatomy and physiology in modern Crocodylia. If I were to critique any particular aspect of the book, it would be the limited references to taxa other the A. mississippiensis and the Australian Crocodylus species. I realize that this is a bias inherent in the literature as it is today, but it is unclear in many sections if the authors elected to focus on these species or if there is virtually no data on other taxa. It would have been more interesting and engaging to have open-ended questions stated explicitly in text. Biology and Evolution of Crocodylians is an expensive book, but it is one that will serve any paleontologist seeking a detailed review of all aspects of modern crocodylian biology. The photographs and illustrations also make it a very attractive book for any natural history enthusiast.
