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The small arms of T. rex may have been useful MNN



The Tyrannosaurus Rex was considered one of the most formidable carnivores of its time. While the debate rages on whether it's a sheer predator or a scavenger, we can all agree that T. rex looks like he knows how to eat a meal.

From his wild appearance, however, were a few small, two-digit claws. They looked as if they belonged to a much smaller creature, not to the so-called king of tyrant lizards.

However, scientists say these stunted arms can still be useful if an analysis of the forelimbs of distant relatives is any indication.

Looking at the Present to Understand the Past

To look at the forelimbs of a T. rex, Christopher Langel, a student of geology, and Matthew Bonnan, a professor of biology, both at Stockton University in New Jersey, looked at the limbs of the domestic turkey (Meleagris gallopavo) and the American alligator (Alligator mississippiensis). They took the ulna and humeral bones of both animals and placed them in two devices that produced a so-called X-ray reconstruction of agitated morphology or XROMM.

The XROMM allows researchers to create a 3D model of the bones of all scanned objects. Movement data is then added to the scan and the result is a 3D moving image that, according to the XROMM website, allows scientists to see "fast bony movements such as during bird flight, frog hopping and human running".

While XROMM can be used with live specimens, Langel and Bonnan used only the extremities of turkeys and alligators for their study. The wings and arms were placed on a Plexiglas platform between the XROMM machines. The two researchers then used fishing wire to pull on the elbows of each limb while the XROMM recorded the bone movements.

 Closeup of the Front Left Front Leg of an Alligator
The American Alligator can help scientists understand how the T. rex moved its arms. (Photo: Wing-Chi Poon / Wikimedia Commons)

The results showed that the elbows of both animals are much more complicated in their movements, much more than ours. "When we bend our elbows, both forearm bones follow the hinge joint to fold to the upper arm," the researchers said on October 17, during the 78th annual Vertebrate Paleontology Society. "Our hands often turn the palm up when we bend our elbows because one forearm bone turns around the other.

"The elbow joint [for turkeys and alligators] is more complex, and both bones in the forearm not only pivot around the joint, but [also] rock sideways to the humerus when the elbow is flexed," the researchers said. "Unlike our elbows, both forearm bones make the palm turn inwards and slightly upwards."

This, according to Live Science, surprised researchers.

"It was particularly surprising to see how much the forearm bones at the elbow can swing from side to side, a movement that is essentially taboo for mammals like us," said Langel and Bonnan. "In principle, alligators and turkeys can turn the palm up and down like us, but [they do it] through more complex movements of the bones on the elbows." Once again, Mother Nature has solved the same problem in various ways. "

Reach something and touch something

 Close-up of a plastic model of T. rex's arms
The T. rex may have kept his arms inboard. (Photo: JopsStock / Shutterstock)

What that means for the T. rex is explained by Live Science as indicating that the dinosaur was a "clapper, not a slapper". That means the T. rex would keep his hands folded inwards as if they were clapping rather than looking down and out as if they were clapping.

The results indicate that the arms of T. rex "may have been able to turn the palm in and out so that the palm of the hand points to the breast as the elbow flexes," the researchers said.

However, why T. rex would do that remains a mystery, because we really can not see the dinosaur in action.

"But we could speculate that such a movement (turning the forearm and hand to chest) could allow some theropods to bite their prey," Langel and Bonnan said in an email to Live Science ,

The research of the duo was not published in a journal.

T. Rex's Tiny Arms May Have Been Useful

According to studies of turkeys and alligators, the researchers speculate that the T. rex could turn its palms in and out – which could affect how and what it eats.


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