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Bone Histology of Fossil Tetrapods: Advancing Methods, Analysis, and Interpretation

Paleohistology has developed significantly over the last 30 years and has become a very fruitful interdisciplinary area of research addressing questions relative to paleobiology and bone tissue evolution. This book followed a National Evolutionary Synthesis Center workshop that took place at the end of 2009, and its intent is to “provide guidance to people new to the field about how to select, process, and image specimens, and about the questions and issues in the field that had been addressed and that need further work” (p. ix), and thereby to introduce paleohistology and its recent advances to beginners and colleagues in related fields. Bone Histology of Fossil Tetrapods is divided into 10 chapters. The first broadly discusses the goals of studying the bone microstructure of fossil tetrapods and introduces the (according to the author) four main signals in fossil bone histology, based on which the histodiversity can be explained: ontogeny, phylogeny, mechanics, and environment. Chapter 2 presents a summary of the basis of bone histology and briefly reviews the early evolution of vertebrate bone tissue types. This chapter deals with the essentials, but it would have been helpful for beginners if it had been more clearly organized and if some illustrations were larger and more extensively labeled. It is maybe unfortunate that, e.g., endosteal and endochondral bones, the differences in cell shape between the various tissue types, metaplastic bone, and osteoderms are poorly or not discussed and that some biological terms possibly outside the repertoire of many paleontologists are not explained. Chapters 3 to 6 deal with methodology. In Chapter 3 are discussed the selection of specimens and the equilibrium required between the need to obtain sufficient material in both quality and number in order to answer the biological questions raised and avoid unnecessary sampling. Chapter 4 is a very large (106 pages) and well-illustrated presentation about how to prepare bones and make histological thin sections. Some sections, notably concerning the equipment required, include too many details and company names. The methods used at the Museum of the Rockies are described in detail and, though excellent, it might have been interesting to mention those used in other histology laboratories. In the last third of the chapter, there is a very dynamic and instructive series of questions and answers. Generally, this chapter is full of recommendations and advice that will be valuable for those wanting to create (or improve) a histology laboratory. As specified at the end, it is written as a guide for technicians with some experience of thinsectioning already. Image acquisition and processing in paleohistology is explained very clearly in Chapter 5. It covers a wide range of technical issues and would be of interest to a large audience. Chapter 6 very clearly explains how to preserve histological samples, images, and data by focusing on specimen and image databases. Chapter 7 discusses the methods and difficulties in analyzing growth marks in bones and the various processes of retrocalculation used to estimate skeletal age and reconstruct skeletochronological trajectories. Chapter 8 reviews recent work on growth rates, discusses both absolute calculations, when growth increments are measured, and relative analyses based on the bone tissue microstructure. It also explains the different purposes of cross-sectional versus longitudinal sampling, evokes the difficulties and interests of mass estimations and linear dimensions, and clarifies some misconceptions about vertebrate growth. Finally, it describes the different models used to build growth curves and the procedures of model selection. Chapter 9 explains how to compare growth rates between taxa in a phylogenetic context in order to investigate growth rate evolution. The concluding chapter discusses the four signals evoked in the introduction in the light of what was covered in the book. It outlines what is known and what remains to be done, notably emphasizing the need for additional comparative data for a large number of extant taxa, and briefly discusses the relationships of paleohistology to other fields of research. As stated in the preface, this book is obviously not exhaustive in its treatment of all subjects relative to bone histology. Regrettably missing, however, is coverage of crystallographic parameters. Furthermore, the four signals reflected in bone tissue are not given equal treatment, the link between bone microanatomy and habitat is hardly evoked, and bones other than long bones are very rarely cited. Moreover, although what is presented can be generalized to all vertebrates, most of the examples focus on dinosaurs and do not reflect vertebrate diversity, and nonpaleontologists can regret that the taxonomy is never detailed. Also, although Bone Histology of Fossil Tetrapods is organized like a paleohistology course, it is not suitable for beginners without any basic knowledge in histology. It is more appropriate for a graduate student wanting to be independent in this type of research, or to scientists wanting to develop paleohistology in their own laboratory. Very few books deal with paleohistology, and those generally focus on specific groups, such as dinosaurs (Chinsamy-Turan, 2005) or therapsids (Chinsamy-Turan, 2012), and only partly deal with histology. Histological techniques were described by Wilson (1994) but in less detail and an update was required. Bone Histology of Fossil Tetrapods is thus a first in being entirely dedicated to paleohistology and in proposing for the first time a very general approach. This well-illustrated and rather complete guide is thus an important book for anyone interested in conducting paleohistological research.