Friday, May 31, 2013

The "Lion of the Jurassic" fed like a falcon

People seem to think that giant predatory dinosaurs were absolute monsters. Of course, they were monstrous in size, with some species reaching upwards of 50ft in length. However, just because they attained these great sizes does not mean they were reckless, ruthless killers. The more we discover about the giant theropods, the more we are able to compose a lifelike and accurate picture of their biology. In recent years, technological advances have allowed us to take a look not only at the surface of fossils, but test their strength and stress under conditions which they would have faced in life.

Recently, the juggernaut theropod Allosaurus, the lion of the Jurassic, was the subject of a study on feeding mechanisms. Combining engineering and technology with a biological perspective allowed Eric Snivley and his team from Ohio University to examine the living mechanics of the predator and determine how it would have fed. They determined that, although Allosaurus was a large predator, it had a very light skull, and its muscles were not suited for vigorous shaking as much as they were for plucking and tearing at flesh.

Allosaurus and Falco. Image coutresy of WitmerLab, Ohio University.

A major find from this study was the placement of the longissimus capitis superficialis muscles on Allosaurus' neck. These muscles, Snivley explains, are comparable to "a rider pulling on the reins of a horse's bridle." If a muscle on either side contracts, then the head moves in that direction, allowing the head to shake from side to side. However, if both muscles contract, the head is pulled directly down. On Allosaurus, these muscles were located very low on the skull, and indicated that the animal drove its head into its prey, held it there, and then tore straight back and up ( This feeding strategy can be seen in modern raptors, including kestrels.

The Jurassic Paleodiet
This comparatively delicate method of feeding, along with the animal's lightweight skull, raise some interesting questions. Allosaurus is commonly portrayed hunting and feeding on the huge sauropods with which it shared its environment. It is true that Allosaurus likely hunted with hatchet-like movements of its skull, slashing through skin and muscle and bleeding out its prey; however, I believe that the possibility of Allosaurus hunting adult sauropods is becoming slimmer and slimmer with each new discovery we make.

Although it was the most abundant large carnivore of the late Jurassic (at least in North America and Europe), it probaby did not hunt the most abundant herbivores, which were the sauropods. I'm sure that allosaurs attempted to tackle juveniles frequently, and probably with some success, but the bulk of their prey likely consisted of animals which were much easier to tackle. Small ornithopods, juvenile stegosaurs, and other small herbivores, as well as small carnivores and many non-dinosaurian prey items, were likely higher of a priority to Allosaurus than the titanic sauropods.

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