An Illustrated Guide to Dinosaur Feeding Biology

This technical book gives a detailed and substantial taxon-by-taxon overview of what dinosaur skulls, jaws, and teeth reveal about what, but especially how dinosaurs ate. This is a welcome survey of an otherwise scattered literature that will be invaluable for specialists. Ali Nabavizadeh is an assistant professor of anatomy and David B. Weishampel a professor emeritus in anatomy and palaeobiology whose name you will undoubtedly recognize.

An Illustrated Guide to Dinosaur Feeding Biology breaks down into roughly two parts, starting with three background chapters. First is a guide to some of the major historical studies and milestones. Second is the basic biology of bones, teeth, and muscles, in particular their functional morphology, which studies what all this anatomy actually does in a living organism. Most of this relies on a solid understanding of, and comparison to, animals alive today. Functional morphology also involves techniques old and modern: bone histology, dental microwear analysis, or biomechanical analysis using techniques borrowed from engineering. Though you would have to look elsewhere for an introduction to biomechanics, my impression is that familiarity with this is not a strict requirement. The third thing you will need is an understanding of (skull) anatomy. This chapter provides names and terminology of cranial bones, muscles, and soft tissues; a primer on postcranial anatomy; and of course the all-important names for directions and orientations when navigating your way around this anatomy.

After this introduction, the bulk of the book consists of ten chapters that give a taxonomic overview. Each chapter opens with a family tree and then per subclade discusses available studies and findings on skulls, teeth, the likely feeding mechanism (i.e. how jaws chewed), inferred musculature, biomechanics (e.g. strains, stresses, and bite forces), the role of postcranial anatomy such as limbs and necks in feeding, and any direct (bite marks) and trace fossil (gastroliths, coprolites) evidence. This is illustrated with drawings of reconstructed heads with overlays of jaw musculature and hypothesized jaw motions, as well as annotated photographs of skulls pointing out relevant and noteworthy features.

What does this survey reveal? When dinosaur feeding biology does make the news, attention usually focuses on carnivorous theropods: apparently, we are all dying to know how hard T. rex's chompers chomped. The answer, as discussed here, is bone-pulverizingly hard. More interesting I found, for instance, the idea that Allosauroids, rather than biting down hard, used their heads like a hatchet, in puncture-pull fashion striking with and then pulling back their head to tear chunks of flesh off the prey. And remember the famous sickle-claw of Deinonychus? Rather than disembowelling prey, it was more likely used to grip and immobilize them, not unlike birds of prey do today.

Now, with all due respect to carnivorous dinosaurs, if this book taught me one thing about jaw mechanics it is that herbivorous dinosaurs is where it is at. For example, next to orthal (up-and-down) motion of the jaws, several groups add propalinal (back-and-forth) motion and even long-axis hemi-mandibular rotation: imagine that each half of your lower jaw could roll sideways, pointing your teeth inwards towards your tongue. Sauropods had unique skulls amongst dinosaurs, with adductor chambers for some of the major jaw muscles positioned below rather than behind the orbits holding the eyes. It is relatively well known that hadrosaurids and ceratopsids had dental batteries. More interesting is how these teeth consisted of not the usual two, but five or six tissue types of different hardness, wearing down in a complex fashion while eating tough and fibrous vegetation.

Equally interesting are the gaps in our knowledge. Except for ankylosaurs, for most groups we have little to no fossilized hyobranchial elements, the bones to which the tongue would have attached in life, meaning we know almost nothing about dinosaur tongues. What happened to diets as dinosaurs grew up? There are only a few taxa for which we have enough baby, juvenile, and adult fossils to construct ontogenetic series, but the results are intriguing. Limusaurus, part of the early theropod subclade Noasauridae, had small teeth as juveniles but lost them as adults, suggesting a shift from omnivory to herbivory. Similarly, the juveniles and adults of both diplodocoids and hadrosaurids differed in cranial and dental morphology, suggesting they fed on different types of plants as they grew up (niche partitioning).

Despite its advanced level and technical detail, this book is accessibly written. You get into the swing of the terminology soon enough and each chapter writes out abbreviations at first use, meaning that you can read the book out of order. Cladograms in each chapter are useful in helping you understand sometimes unwieldy descriptors such as "non-ceratopsoid ceratopsians". I have two minor nitpicks. First, I would not have minded if the authors had organized information for each subclade with further subheadings. The information is all there, and each chapter discusses skulls, teeth, biomechanics, etc. in the same order, but for intensively studied groups, this results in pages-long uninterrupted blocks of text. Some extra signposting would have helped navigate and later relocate information. Second, the drawings are very useful, though stylistically it feels Nabavizadeh is overusing the smudge/airbrush tool to smooth out textures. I actually prefer the few drawings where he has not done so, such as the comparison of Centrosaurus and Chasmosaurus on page 281. The use of white gradients around the arrows labelling photos and drawings is a lifesaver, however; it would have been impossible to tell what they are pointing to otherwise.

So, who is this book for? For palaeontologists and especially those working on dinosaur feeding biology, or facets thereof, this will be a very welcome overview, with the 38 pages of references being a goldmine of curated literature. For students entering this field, a book like this is a godsend. For the wider audience of dinosaur enthusiasts and palaeontology fanatics, this book should be, as mentioned earlier, accessible enough. If you take an undergraduate textbook such as Fastovsky & Weishampel's Dinosaurs as your starting point, An Illustrated Guide to Dinosaur Feeding Biology would be the logical and manageable follow-up to deepen your knowledge on the topic. I, for one, cannot get enough of these kinds of advanced-level syntheses and enjoyed ploughing through this book.