Theropod Teeth and Feeding Styles

Dinosaur teeth, particularly those of theropods, are among the most common type of fossil found with the remains of these extinct creatures. The hard, enameled construction of teeth improved their chances of becoming fossilized, and some specimens still retain their original, enamel outer surface. Sometimes the only clue to the presence of a theropod is a tooth that it left behind. Fossil teeth have been found singly, without any other associated body parts, embedded in the bones of fossilized prey. Other teeth, most dramatically, have been found in association with the skull and jaws of a theropod fossil.

Teeth can be highly informative. In most cases, the general shape, size, and structure of a tooth immediately identifies its owner as being a carnivore or a herbivore. Pointed, serrated teeth are associated with carnivorous dinosaurs. Despite a superficial similarity in the shape and structure of theropod teeth among different taxa, closer examination can reveal subtle clues that disclose the kind of dinosaur that had a given tooth, its method of biting prey, and its eating habits.

Theropod teeth fall into three morphological categories, and each of these categories can be associated with a general group of predatory dinosaurs. The largest and most robust teeth were those of tyrannosaurs. The teeth of T. rex and its kin were as long and thick as bananas, deeply rooted, and sturdy enough to withstand contact with bones. Most other theropods had more bladelike teeth that were thinner and more razorlike than the teeth of tyranno-saurs. The third kind of theropod tooth was that of the spinosaurs, giant carnivores with gavial-like snouts. Spinosaur teeth were conical rather than bladelike, sharply pointed, and often not serrated.

The ways in which a theropod bites and uses its teeth are related to two aspects of the animal's anatomy and physiology: tooth design and cranial mechanics.

Tooth Design

Theropod teeth have been collected by paleontologists for nearly 200 years. The most typical theropod tooth had a slightly curved and pointed profile, with a bladelike shape and serrations on the forward and backward edges. Serrations consist of tiny undulations or bumps arranged in a tightly conforming row along the edge of the tooth. Serrations vary somewhat in shape from one kind of theropod to another, but most serrations are generally square and capped with tooth enamel.

The bladelike shape and serrated edges of theropod teeth led to a conventional view that they operated more or less like steak knives, slicing through the side of a prey animal with the ease of a knife through a juicy cut of meat. This view has changed since American researcher William Abler began examining the mechanical action behind serrated tooth designs. In 1992, Abler set out to take a close, comparative look at different kinds of theropod teeth to ascertain how they actually cut through meat. He did this by fashioning steel hacksaw blades to mimic a variety of serration patterns, in particular those of the giant carnivore Tyrannosaurus and the smaller, more ostrichlike Troodon (Late Cretaceous, western North America). Through his experiments, Abler identified two distinctive biting mechanisms at work in theropods with bladelike teeth.

Shapes and structure of theropod teeth

The fat, robust teeth of T. rex had an innate gripping action associated with "tiny frictional vises" between neighboring serrations. The teeth of T. rex could not slice through meat with the ease of a sharp steak knife as once had been thought. Abler characterized the biting action of such robust teeth as a "grip and hold" action. T. rex muscled its way through dinner, grabbing, crushing, and tearing off chunks of meat. Theropods such as Troodon, with thinner, sharper, bladelike teeth, could more easily slice through meat using an action that Abler called "grip and rip"—an action more like that of the traditional steak knife.

Abler's examination of T. rex teeth revealed another surprise. The tiny gripping surfaces between the serrations of T. rex teeth were capable of snagging tiny fibers of meat that were difficult to remove. Abler speculated that the pockets trapped grease and spawned infectious bacteria on the biting edges of the teeth, essentially transforming the teeth of T. rex into a poison-tipped dental arsenal. An animal bitten by T. rex that escaped immediate death may have become sick enough from the toxic bite to weaken soon thereafter, while the lumbering T. rex followed not too far behind to finish it off. As speculative as this seems, a similar behavior is seen today in the Komodo dragon of Indonesia.

The Cranial Mechanics of Feeding Style

Abler's work on the innate cutting ability of serrated teeth was provocative. He reasoned that evolution produced teeth that were optimally designed for the lifestyle of a given dinosaur, and that understanding how the teeth worked could reveal aspects of a given theropod's lifestyle. This led to additional studies of theropods that modeled the action of the teeth within the context the animals' cranial mechanics.

Paleontologist Emily Rayfield of Cambridge University is a leading expert in the bite and stress forces that probably took place in the skull of a theropod when it fed. She has conducted noninvasive studies of fossil theropod skulls using computed tomography (CT) scans and engineering software normally applied to building mechanics. Using these technologies, Rayfield has been able to model the strong and weak points in various theropod skulls and suggest the ways the animals probably used their teeth when feeding. Her conclusions nicely dovetail with the tooth functions suggested by Abler.

Abler's "grip and hold" view of T. rex tooth design fits well with Rayfield's conclusion that tyrannosaurs used a "puncture and pull" technique when feeding. The big bite and bone-crushing teeth of T. rex would close on the prey and hold fast while the predator pulled back to rip off meat. A separate study by paleontologist Greg Erickson of the University of California, Berkeley, provided hard fossil evidence for the "puncture and pull" technique in the form of a Triceratops (Late Cretaceous, western North America) skeleton with bite marks that matched the puncture size of T. rex teeth.

In contrast to the "puncture and pull" technique was the feeding style of theropods with more slender, bladelike teeth, such as Coe-lophysis and Allosaurus. Rayfield's modeling of the skulls of those two theropods suggested that the power of the bite was focused at the front of the jaw, resulting in a "slash and tear" approach to feeding that reduced stress on the animals' teeth. In this scenario, a theropod would grip the prey with its front teeth and swing its head from side to side to rip off meat. This view fits nicely with the "grip and rip" tooth action described by Abler for this style of theropod tooth.

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