Tyrannosauridae (meaning “Tyrant Lizard”) was a family of dinosaurs that lived during the Late Cretaceous period approximately 60 million years ago. Tyrannosaurids were almost always the largest predators of their habitats, and Tyrannosaurus rex is one of the most famous meat-eaters of all time. At up to 40 feet in length and 7.2 tons in weight, T. rex is aptly dubbed the “King of Lizards.” The only small and non-threatening part of the great predator was its puny arms, which had only two functioning digits.

A recent study published in the Journal of Zoology claims these arms were even more useless than previously believed. Researchers now assert that tyrannosaurids’ necks were so powerful that all grasping, pulling, striking, and clenching the great predator performed was done with its jaws and neck. The study, headed by Eric Snively of the University of Wisconsin–La Crosse and his colleagues, analyzed the physiology of the neck bones left behind by fossilized tyrannosaurids to determine how the neck muscles must have been attached to the skeleton. Then, scientists compared this musculature to the physiology and function of neck muscles in birds of this era.

It has been common scientific knowledge for a time that today’s birds are the closest living relative of dinosaurs. Indeed, the raptors of today (eagles, hawks, falcons) can trace their heritage directly back to the raptors of the Cretaceous (Velociraptor and Utahraptor), and a little farther to the other theropodssuch as the tyrannosaurids. Also closely related are modern day crocodilians. By studying how the muscles in crocodiles, alligators, eagles, hawks, falcons, and chickens work as they feed, scientists could make inferences about how similar muscles must have worked in tyrannosaurids.

Researchers headed by Eric Snively of the University of Wisconsin–La Crosse and his colleagues, attached myocardiogram instruments to the heads and necks of various birds. The instruments showed what muscles were contracting when the birds performed different feeding maneuvers. They found that the birds often raised their heads and set their eyes on prey before lowering their heads and attacking. Tyrannosaurids had many of the same muscles, suggesting they would perform similar movements – including raising the head, thrusting it upwards, and pulling back with the legs to remove flesh once the dinosaur has taken a bite.

Birds and crocodiles alike would also shake the prey in their mouth from side to side once taking a bite, perhaps to better remove flesh or to more quickly subdue prey. The main muscles involved in this motion are also present in the necks of tyrannosaurids. Scientists purport that the massive predators likely struck their prey like a bird (the way you see a hawk or eagle striking its meal) and then shook it like a crocodile, using similar powerful neck musculature.

Snively said “Tyrannosaurs didn’t need big arms to hunt, because their powerful bites and hyper-bulldog necks did the job. From the shoulders forward, T. rex was like a whole killer whale: just bite, shake and twist.”

It would seem jokes about the uselessness of T. Rex arms are even truer than previously thought, but with such a strong neck to support powerful jaws, Tyrannosaurs were just as mean a predator as there ever was.

Snively, E., Russell, A. P., Powell, G. L., Theodor, J. M., & Ryan, M. J. (2014). The role of the neck in the feeding behaviour of the Tyrannosauridae: inference based on kinematics and muscle function of extant avians. Journal of Zoology, 292(4), 290-303. doi:10.1111/jzo.12109.

The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.

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Published On: June 2, 2014

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