Dinosaur chomped like a bird of prey, say scientists

A study of an Allosaurus fossil found that the massive dinosaur dined more like a kestrel than a crocodile, tearing flesh from carcasses by pulling its head straight back. 

At first glance, a nearly 30-foot long, 150-million-year-old dinosaur may not seem to have much in common with a modern-day bird of prey, but according to new research, the Allosaurus and the falcon at least had the same table manners.

In a study published this week in the journal Palaeontologia Electronica, Ohio University researchers used a CT scanner to create a digital image of an Allosaurus fragilis skull. After adding neck and jaw muscles, air sinuses, and a windpipe to the image, they then, using a physics simulator, modeled how the dinosaur would have moved its head.

They found that, unlike the Tyrannosaurus, which paleontologists say dismembered its victims by thrashing its head from side to side like a crocodile, the Allosaurus, which, like Tyrannosaurus walked on two legs and had stubby forelimbs, most likely dined by biting into its prey and then tearing the flesh retracting its head back and upward.

Their discovery hinged on a neck muscle that was unusually positioned on the Allosaurus. On most predatory dinosaurs, such as the T. rex the longissimus capitis superficialis runs along the side of the neck, where it attaches to a bony protrusion at the base of the skull. But on the Allosaurus, the muscle is attached much lower on the skull. 

"This neck muscle acts like a rider pulling on the reins of a horse's bridle," said  Ohio University paleontologist Eric Snively, the study's lead author, in an Ohio University press release. "If the muscle on one side contracts, it would turn the head in that direction, but if the muscles on both sides pull, it pulls the head straight back."

Most Allosaurus specimens, including the one used in this study, have been unearthed in the western United States, in a fossil-rich region known as the Morrison Formation. During the late Jurassic period, about 150 million years ago, the Allosaurus sat at the top of the food chain. In 2005, paleontologists detailed evidence of combat between Allosaurus and Stegosaurus, suggesting that the armored quadroped was on the Allosaurus's menu.

The Tyrannosaurs lived much later, about 65 million years ago.

"Apparently one size doesn't fit all when it comes to dinosaur feeding styles," said Dr. Snively. "Many people think of Allosaurus as a smaller and earlier version of T. rex, but our engineering analyses show that they were very different predators."

Both genuses are theropods, a group of two-legged dinosaurs that includes today's birds. In other words, the Allosaurus and the falcon have at least one more thing in common: they are both dinosaurs.