Researchers Find First Known Fossils of Cat-Sized T. rex Hatchlings

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Paleontologists examining collections of small dinosaur bones tucked away in drawers have uncovered what researchers identify as the first known fossils of Tyrannosaurus rex hatchlings. Nicholas Longrich, a paleontologist and evolutionary biologist at the University of Bath in England, stumbled upon a tiny third metatarsal, or foot bone, in the collection of the Royal Saskatchewan Museum’s T. rex Discovery Centre in Canada. Longrich noted that the bone varied in appearance from other theropod bones he had seen, describing It doesn’t match anything I’ve seen before and adding It just didn’t seem to fit in any of the categories as reported by FOX Weather.

The discovery of a tiny baby Tyrannosaurus rex foot bone gave researchers insight into what T. rex reproduction looked like, from how big a clutch of eggs was to how large the T. rex hatchlings were. Nicholas Longrich, along with other researchers, made this discovery while going through collections of small dinosaur bones that were tucked away and typically misidentified. In a video posted to his YouTube page, Longrich described how he stumbled upon such a rare find, saying he couldn’t make sense of a third metatarsal or foot bone of what was believed to be a theropod dinosaur.

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Upon taking a closer look, researchers realized the bone possessed a porous texture typical of an immature dinosaur. By process of elimination, this is the foot bone of a very, very tiny T. rex, Longrich said, calling it This is the smallest T. rex that we’ve ever seen. The discovery, detailed in a study published in the journal Biology, also included a hatchling foot bone from the related predator Gorgosaurus libratus along with several shed teeth scattered among museum collections. Together, the fossils suggest that newborn tyrannosaurs moved soon after hatching, fed themselves and probably emerged in clutches numbering in the dozens.

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To understand the age and lifestyle of the animals, researchers used high-tech computed tomography (CT) equipment to examine the inner tissue of the T. rex foot bone. The researchers scanned the foot bone fossil at the Canadian Light Source at a resolution of 4.4 microns, allowing them to trace microscopic canals through the bone. The scans revealed no growth rings, confirming that the specimen came from an individual less than a year old. The inner tissue was porous and crowded with blood-vessel channels, indicating extremely rapid growth, while the denser outer layer appeared to have formed after hatching.

Eric Snively at Oklahoma State University worked with the fossils, and Snively saw the potential immediately. Metatarsals of a baby Tyrannosaurus might tell us if the babies were hunting right away or were in the nest for a longer time, Snively said in a statement. Both species displayed persuasive dental and vascular evidence that their little infant progeny were actually quite active and quite lethal.

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At 5.5 pounds (2.5 kilograms) — with a body weighing perhaps 3.7 pounds (1.6 kg) at hatching — baby T. rex was no bigger than a house cat. Tyrannosaurus were unsafe at any size, study co-author and Oklahoma State University anatomy professor Eric Snively said in a statement. Babies were quickly out of the nest and killing the heck out of things. The babies were smashing into the bones of their food, just like giant adults, according to Snively, hitting the ground running, scarpering around and devouring relatively large prey shortly after birth. Combined with previous evidence of worn teeth from T. rex hatchlings, this showed that T. rex was not waiting around, coming out of the egg ready to chase its own food rather than relying on its parents like most modern birds.