T. rex’s short arms may have reduced the risk of bites during binge eating

T. rex is probably the most famous dinosaur of all, but for years a key question about its anatomy has lingered — why were its arms so short?

Now an American paleontologist has claimed that the fearsome creature has evolved stumpy arms to keep it out of the way when it gorges.

Short arms may have reduced the risk of being bitten by other hungry T. rex adults while devouring a carcass.

The tiny arms of the otherwise mighty Tyrannosaurus rex are one of paleontology’s greatest and enduring mysteries.

For example, a 45-foot T. rex might have a five-foot skull but arms only three feet long—equivalent to a 6-foot human with 5-inch arms.

According to the Natural History Museum, Tyrannosaurus rex is one of the most fearsome animals that ever existed – but why did it have such small arms? Shown here is a tyrannosaurus eating its prey – a dead hadrosaurus

Ancestors of tyrannosaurids had longer arms, so there must have been a reason they were reduced in both size and joint mobility.  Here is an artist's rendering of a T. rex

Ancestors of tyrannosaurids had longer arms, so there must have been a reason they were reduced in both size and joint mobility. Here is an artist’s rendering of a T. rex

T. rex and other tyrannosaurids first appeared in the late Jurassic and peaked in the late Cretaceous before becoming extinct around 65.5 million years ago.

WHAT WAS T.REX?

Tyrannosaur Rex was a type of bird-like, carnivorous dinosaur.

It lived 68 to 66 million years ago in what is now western North America.

They could grow up to 12 meters long and 4 meters high.

More than 50 fossilized specimens of T.Rex have been collected so far.

The monstrous beast had one of the strongest bites in the animal kingdom.

The new study was led by paleontologist Kevin Padiana, a professor at the University of California, Berkeley, and curator at the UC Museum of Paleontology (UCMP).

Professor Padian noted that the tyrannosaurid ancestors had longer arms, so there must have been a reason they were reduced in both size and joint mobility.

The answer came to him after other paleontologists found evidence that some tyrannosaurids hunted in packs, not individually as depicted in many paintings and dioramas.

“What if several adult tyrannosaurs converged on a carcass?” he said. “You have a bunch of massive skulls with incredibly powerful jaws and teeth that tear and crush flesh and bone right next to you.

“What if your friend over there thinks you’re getting a little too close? They could warn you by cutting off your arm,’ he said.

“So it might be an advantage to reduce the front legs since you don’t use them for hunting anyway.”

When he taught a freshman seminar called The Age of Dinosaurs, Professor Padiana was always asked by students why T. rex’s arms were so ridiculously short, but the answer was always, “Nobody knows.”

When the great dinosaur hunter Barnum Brown discovered the first T. rex fossils in 1900, he thought the arms were too small to be part of the skeleton.

A life-size cast of the T. rex in the atrium of UC Berkeley's Valley Life Sciences Building shows how unusually short the dinosaur's forearms were considering the creature was the fiercest predator of its time

A life-size cast of the T. rex in the atrium of UC Berkeley’s Valley Life Sciences Building shows how unusually short the dinosaur’s forearms were considering the creature was the fiercest predator of its time

T.REX ENJOYS A COMFORTABLE WALK AT JUST 4.8 MPH, RESULTS OF ANALYZING THEIR COCKS

The fearsome Tyrannosaurus rex (T. rex) enjoyed a “slow” stroll at just 2.8 miles per hour (4.6 km per hour), a new study shows.

scientist in Netherlands developed a new method for estimating the preferred walking speed of T. rex based on analysis of a preserved specimen named Trix.

They say their new speed estimate is similar to the natural walking speed of emus, elephants, horses and humans – and lower than previous estimates.

Key to the study was Trix — the 6-ton, 43-foot-long (13-meter) female T-Rex whose complete and superbly preserved skeleton was unearthed in Montana in 2013.

Trix – currently on display at the Museum Naturalis – lived 66 million years ago in what is now western North America, on an island continent then known as Laramidia.

Continue reading: T-Rex roamed the earth at a “slow” pace, a study has found

Back then, his colleague Henry Fairfield Osborn, who described and named T. rex, hypothesized that the short arms might have been “breast clamps” — limbs that hold the female in place during copulation.

This is analogous to the pelvic clasps of some sharks and rays, which are modified fins.

But Osborn provided no evidence, and Professor Padian has determined that the T. rex’s arms are too short to bypass another T. rex, and certainly too weak to exert any control over a partner.

For more than a century, other proposed explanations for the short arms have included waving for mate attraction or social signals, serving as an anchor to allow T. rex to get up off the ground, hold down prey, stab enemies, and even poke over a nocturnal sleeping Triceratops, like cow butts.

Also, some paleontologists have suggested that the arms have no function at all, so let’s ignore them.

In his paper, Professor Padiana proposes his new hypothesis – T. rex arms were shrunk to prevent accidental or deliberate amputation when a pack of T. rex fell on a carcass with their massive heads and bone-crushing teeth.

Perhaps in the few million years that the species has existed, the arms have shrunk to get out of the way when feeding in packs.

Juvenile T. rex in particular would have been wise to wait until the larger adults had finished eating.

This is similar to the largest extant species of lizard, the giant Komodo dragon lizard (Varanus komodoensis) from Indonesia.

This extant species hunts in groups, and when killing prey, the larger dragons converge on the carcass, leaving the remains for the smaller ones.

Professor Padiana has admitted that 66 million years after the last T. rex went extinct, any hypothesis, including his, will be difficult to support.

Artist's rendering of a Tyrannosaurus Rex and its cubs feeding on an Alamosaurus carcass

Artist’s rendering of a Tyrannosaurus Rex and its cubs feeding on an Alamosaurus carcass

The giant Komodo dragon lizard (Varanus komodoensis, pictured) hunts in groups and when it kills prey, the larger dragons run towards the carcass, leaving the remains for the smaller ones

The giant Komodo dragon lizard (Varanus komodoensis, pictured) hunts in groups and when it kills prey, the larger dragons run towards the carcass, leaving the remains for the smaller ones

“Several important quarry sites excavated over the past 20 years keep adult and juvenile tyrannosaurs together,” he said.

“We can’t really assume that they lived together or even died together. All we know is that they were buried together.

“But if you find multiple sites with the same animals, that’s a stronger signal. And the possibility that other researchers have raised is that they hunted in groups.’

Further research could reanalyze the fossils of T. rex arms for bite marks.

‘Bite wounds on the skull and other parts of the skeleton are known to occur in tyrannosaurs and other carnivorous dinosaurs,’ Professor Padiana said.

“If fewer bite marks were found on the reduced limbs, this could be a sign that the reduction worked.”

The study was published in the journal Acta Palaeontologia Polonica.

T.REX COULD ACTUALLY HAVE BEEN THREE SPECIES, NOT ONE, FOSSIL ANALYSIS REVEALS

T.Rex may actually have been three species, not one, a recent fossil analysis shows.

US scientists re-analyzed nearly 40 fossilized tyrannosaurus skeletons found by paleontologists over the course of more than a century.

Among the specimens examined was “Sue,” a complete tyrannosaurus skeleton currently housed in the Field Museum of Natural History in New York Chicagoand ‘AMNH 5027’, known to be found at Big Dry Creek, Montana1908

They found physical differences in the femur, or femur, as well as tooth structures and other bones in the specimens — evidence that points to three different species of Tyrannosaurus.

The researchers suggest that the larger specimens found should be attributed to a new species they call Tyrannosaurus imperator (tyrant lizard emperor).

The smaller, slimmer specimens, on the other hand, should be attributed to a species they call Tyrannosaurus regina (tyrant lizard queen), they say.

Continue reading: T.Rex may actually have been THREE species, fossil analysis shows

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