In the case of figuring out fossil species, a lone leg bone isn’t a lot to go on. But a brand new evaluation of a giant fossil tibia suggests it provides a clue to the origins of Tyrannosaurus rex, the hulking, sharp-toothed apex predator that dominated the twilight of the Age of Dinosaurs.
The bone’s sheer dimension hints that it was a tyrannosaurid, a gaggle that features essentially the most large members of the tyrannosaur household tree, researchers declare in a research printed March 12 in Scientific Stories. Tyrannosaurids lived late within the Cretaceous Interval, between 83 million and 66 million years in the past, and have been discovered solely in Asia and North America. This tibia was present in rocks that date to about 74 million years outdated.
T. rex advanced within the ultimate a part of the Cretaceous, in what’s now northern North America, about 68 million to 66 million years in the past, the youngest, greatest and most extremely specialised predator of the group. But the origins of the long-lasting dino are murky. Probably the most extensively accepted speculation is that its large-bodied ancestors migrated throughout a land bridge from Asia; that’s supported by T. rex’s putting similarity to Tarbosaurus, a tyrannosaurid that lived in what’s now Mongolia and China.
However a big tyrannosaurid residing just a few million years earlier in southern North America lends assist to a unique speculation, says Nick Longrich, a paleontologist on the College of Bathtub in England. As an alternative of journeying from Asia, tyrannosaurids residing in what’s now southern North America could have migrated northward, he says.
The tibia, which is about 96 centimeters lengthy, is a part of a set of bones discovered within the Kirtland Formation of New Mexico and housed for many years on the New Mexico Museum of Pure Historical past and Science in Albuquerque. The bone was surprisingly large, much more so than these of older tyrannosaurs reminiscent of Albertosaurus discovered elsewhere in North America, Longrich says.
“It was this huge bruiser of a shinbone,” Longrich says. The workforce estimated that the creature it belonged to should have had a physique mass of about 4.5 metric tons. For comparability, Albertosaurus was as much as 3 metric tons, whereas T. rex weighed as much as 9 metric tons.
The shinbone’s proprietor was maybe “small by Tyrannosaurus requirements, however perhaps 50 p.c greater than something we all know of from that point interval,” Longrich says. “Simply actually chunky.”
But it surely’s nonetheless only one leg bone, different researchers say, and that’s simply not sufficient to attract agency conclusions about what sort of animal it belonged to, not to mention questions of T. rex’s origins. “These are fairly unbelievable claims a few single bone that’s not effectively preserved,” says Thomas Carr, a paleontologist at Carthage School in Kenosha, Wis., who was not concerned within the research.
Carr says he’s not satisfied that there’s sufficient proof to recommend the bone should have belonged to a tyrannosaurid, versus, say, Bistahieversor, a smaller tyrannosaur nicknamed the “Bisti Beast” that was already recognized to reside in that very same time and place. “In my opinion, the null speculation is that the tibia is from a big and heavy Bistahieversor, since no different tyrannosaurids are recognized from that geological unit.”
The brand new research suggests the leg bone is each too huge and the fallacious form to belong to Bistahieversor, however tyrannosaur leg bones are tough, Carr says. The leg bones of juvenile tyrannosaurids reminiscent of T. rex are recognized to be markedly completely different from grownup leg bones, in that they’re thinner and extra bowed. Because the creature grows, its leg bones bulk as much as bear the animal’s weight or else shatter. “Functionally, [these creatures are] all the identical: They run round killing issues then get outdated and massive and stroll round killing issues.”
“The underside line,” Carr says, “is that they haven’t demonstrated convincingly that the similarities between that tibia and people of tyrannosaurids isn’t merely the consequence of enormous dimension.”
