Adolescent Tyrannosaur Multi-Step Tracks Are The First Of Their Kind

The first track at the dig site, made by either Tyrannosaurus rex or Nanotyrannus lancensis. Scott Persons

An incredibly rare set of Tyrannosaurus rex tracks have been discovered in Wyoming. These multi-step tracks are the first of their kind, and interestingly they don’t belong to an adult – these appear to have been made by an adolescent, as a study in the journal Cretaceous Research reveals.

Inarguably one of the most famous dinosaurs, the T. rex (“tyrant lizard king”) was a fearsome beast that weighed up to 5 tonnes (5.5 tons) and grew up to 12.3 meters (40 feet) in length.

Although there is an ongoing debate as to whether it was a true carnivore, a scavenger or even a cannibal, no paleontologist doubts its ferocity. And frighteningly, a recently discovered series of tracks suggests that tyrannosaurs may have even hunted in packs. The terrifying image of several of them chasing after a hapless herbivore at speeds of up to 29 kilometers per hour (18 miles per hour) can only be mediated by one thing: at that speed, if one tripped, it would fall to the ground so hard that it would crush its own skull.

Despite the wealth of knowledge paleontologists have on tyrannosaurs, finding tracks made by the Upper Cretaceous (100 to 66 million years ago) apex predators has proven very difficult. Fortunately, a team of researchers from the University of Alberta have found some just outside Glenrock, Wyoming, dated to be 66 million years old – tracks made right at the end of the age of the dinosaurs.

“Jane,” an 11-year-old juvenile T. rex specimen at the Burpee Museum of National History at Rockford, Illinois. Volkan Yuksel/Wikimedia Commons; CC BY-SA 3.0

The three front sharp claws, the presence of a smaller fourth claw at the rear, and the size of the prints themselves – 47 centimeters (18.5 inches) across – indicate that they belonged to a huge carnivore. Only two possibilities fitted the bill: T. rex, or Nanotyrannus lancensis. Although individual tyrannosaur footprints have been found before, these are the first multi-step tracks belonging to T. rex or N. lancensis known to science.

As the name might suggest, the N. lancensis was a closely related but somewhat smaller dinosaur than its more famous cousin – although it was still no small fry, with one specimen measuring 5.2 meters (17 feet) long. However, several paleontologists think that the two (possibly three) specimens of N. lancensis are in fact just juvenile T. rex specimens, so the species designation remains controversial.

If the tracks did belong to a T. rex, however, it certainly wasn’t an adult. “The tracks are just a bit too small to belong to a full grown T. rex,” paleontologist Scott Persons, one of the co-authors of the paper, said in a statement. “But they could very well be the tracks of an adolescent Tyrannosaurus rex.”

Either way, these multi-step tracks allowed the researchers to estimate the speed at which this ancient beast was running when it made them. At just 4.5 to 8 kilometers per hour (2.8 to 5 miles per hour), this puts it at a slow trot. This speed, nevertheless, would have been enough for it to catch up with its prey – large, herbivorous hadrosaurs – that it presumably hunted at the time.

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