Washington: It is believed that the mighty T. rex may have thrashed its massive head from side to side to dismember prey, but a new study has shown that its smaller cousin Allosaurus was a more dexterous hunter and tugged at prey more like a modern-day falcon.
"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," said Ohio University paleontologist Eric Snively, lead author of the new study.
Snively led a diverse team of Ohio University researchers, including experts in mechanical engineering, computer visualization and dinosaur anatomy. They started with a high-resolution cast of the five-foot-long skull plus neck of the 150-million-year-old predatory theropod dinosaur Allosaurus, one of the best known dinosaurs.
They CT-scanned the bones at O`Bleness Memorial Hospital in Athens, which produced digital data that the authors could manipulate in a computer.
Snively and mechanical engineer John Cotton applied a specialized engineering analysis borrowed from robotics called multibody dynamics. This allowed the scientists to run sophisticated simulations of the head and neck movements Allosaurus made when attacking prey, stripping flesh from a carcass or even just looking around.
To figure out how Allosaurus de-fleshed a Stegosaurus, the team had to "re-flesh" Allosaurus. The anatomical structure of modern-day dinosaur relatives, such as birds and crocodilians, combined with tell-tale clues on the dinosaur bones, allowed Snively and anatomists Lawrence Witmer and Ryan Ridgely to build in neck and jaw muscles, air sinuses, the windpipe and other soft tissues into their Allosaurus 3D computer model.
A key finding was an unusually placed neck muscle called longissimus capitis superficialis. In most predatory dinosaurs, such as T. rex, which Snively studied previously, this muscle passed from the side of the neck to a bony wing on the outer back corners of the skull.
"This neck muscle acts like a rider pulling on the reins of a horse`s bridle. 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," explained Snively.
But the analysis of Allosaurus revealed that the longissimus muscle attached much lower on the skull, which, according to the engineering analyses, would have caused "head ventroflexion followed by retraction."
"Allosaurus was uniquely equipped to drive its head down into prey, hold it there, and then pull the head straight up and back with the neck and body, tearing flesh from the carcass ... kind of like how a power shovel or backhoe rips into the ground," Snively said.
In the animal world, this same de-fleshing technique is used by small falcons, such as kestrels. Tyrannosaurs like T. rex, on the other hand, were engineered to use a grab-and-shake technique to tear off hunks of flesh, more like a crocodile.
But the team`s engineering analyses revealed a cost to T. rex`s feeding style: high rotational inertia. That large bony and toothy skull perched at the end of the neck made it hard for T. rex to speed up or slow down its head or to change its course as it swung its head around.
Allosaurus, however, had a relatively very light head, which the team discovered as they restored the soft tissues and air sinuses.
"Allosaurus, with its lighter head and neck, was like a skater who starts spinning with her arms tucked in," said Snively, "whereas T. rex, with its massive head and neck and heavy teeth out front, was more like the skater with her arms fully extended ... and holding bowling balls in her hands. She and the T. rex need a lot more muscle force to get going."
The end result is that Allosaurus was a much more flexible hunter that could move its head and neck around relatively rapidly and with considerable control. That control, however, came at the cost of brute-force power, requiring a de-fleshing style that, like a falcon, recruited the whole neck and body to strip flesh from the bones.
Results of the new study have been published in Palaeontologia Electronica.