T. Rex's weak arms were useful after all

A fossil of a Tyrannosaur rex known as "Sue" was seen at the Field Museum in Chicago on October 6, 2016.
(Reuters)

ALBUQUERQUE, N.M. – Tyrannosaurus rex and other meat-eating dinosaurs are often ridiculed for their ridiculously puny arms, but new research indicates that these dreaded predators could do much more with these smaller members than previously thought.

By studying the movements of the arms of two distant parents T. rex – the domestic turkey (Meleagris gallopavo) and the American alligator (Alligator mississippiensis) – researchers have learned that T. rex and other theropods (a group of bipedal dinosaurs eating mostly meat) could probably turn the palms of their hands towards their chests.

In essence, "they may have been able to rotate the palm of the hand inward and upward so that the palm of the hand was facing the chest when the elbow was flexed", Christopher Langel, a junior co-investigator in geology, and Matthew Bonnan, a professor of biology at Stockton University in New Jersey, told Live Science. [Photos: Newfound Dinosaur Had Tiny Arms, Just Like T. Rex]

This adds to the popular saying that says "T. rex was a fighter not a fighter, "in the way he held his hands. In other words, the dinosaur probably kept his hands in a position of applause (palms facing inward) rather than a slapping position (palms facing downwards). But the king dinosaur was not limited to applauding: the new research suggests T. rex and other theropods could turn their palms inward and upward if they wished.

As to why this would be beneficial, it is difficult to say with certainty without seeing a ferocious nonavian theropod in action, the researchers said. "But we could assume that such a movement (rotation of the forearm and hand towards the chest) could allow some theropods to approach their prey for a mouthful," Langel said. Bonnan to Live Science in an email.

In fact, the next stage of research scientists could shed light on this issue. The team plans to examine the shape of the bones of the anterior legs of the theropod Allosaurus and compare them with those of alligators and turkeys "to help us determine if this could actually occur in a theropod dinosaur," said Langel and Bonnan. Both presented their research at the 78th Annual Meeting of the Society of Vertebrate Paleontology yesterday (17 October). The research has not yet been published in a peer-reviewed journal.

Turkey time

The researchers could not just study a T. rex arm, because the soft tissues of the joints rarely fossilize. "As a result, we lack information about the forms of the [theropod] The joints really looked like and how far apart were the bones when the predatory dinosaur was alive, "said Langel and Bonnan.

To investigate, the researchers examined the ulna and the humerus in alligator and turkey with a technique called X-ray reconstruction of moving morphology, or XROMM. First, the investigators attached each wing and each arm to a Plexiglas platform between two devices generating X-ray film. Then the researchers used a fishing line to pull the elbow of each specimen, which caused the wing and arm to fold, the researchers said. [Image Gallery: The Life of T. Rex]

Finally, "we used the two x-ray views of each elbow to reconstruct the way the bones moved in three dimensions by precisely matching the virtual models of each bone to the movies," said the researchers.

The results showed just how complex turkey and alligator elbows are. In humans, "when we bend our elbows, the two bones of the forearm follow the hinge joint to fold up to the upper arm," the researchers said. "Our hands often turn the palm of our hand when we bend our elbows, as one forearm bone pivots around the other."

In contrast, in alligators and turkeys, "the elbow joint is more complex and the two forearm bones pivot not only around the joint, but [also] rock the stone laterally to the arm bone when the elbow is flexed, "said the researchers. Unlike our elbows, the two bones of the forearm [in alligators and turkeys] bring the palm of your hand to turn inward and slightly upward ".

These results were somewhat unexpected, the scientists said.

"It was particularly surprising how much the forearm bones could tilt from one elbow to the other, a movement that is essentially forbidden to mammals like us," said Langel. and Bonnan. "Essentially, alligators and turkeys can turn the palm of the hand inward and upward as we do, but [they do it] using more complex movements of the bones of the elbow. Once again, Mother Nature solved the same problem in different ways. " [Dinosaur Profile: Tyrannosaurus Rex (Infographic)]

Other paleontologists were impressed by the approach of the team.

"If we simply examined the bones without considering cartilaginous reconstructions, we could potentially lose different results as to how to reconstruct the movement of the limb joints," said Viktor Radermacher, a master's student in paleontology at the university. University of the Witwatersrand in Johannesburg, South Africa, which did not participate in the research, told Live Science. "And that has far-reaching implications down the way we interpret the ancestral things that then evolve into more specialized forms and understanding of that transition."

Matthew Inabinett, a paleontology graduate student at East Tennessee State University who did not participate in the research, nodded. "It's easy to forget how soft tissue and cartilage play a role" in the movement of creatures who died so long ago, Inabinett told Live Science.

Originally published on Science live.