T. rex fossils reveal newborn dinosaurs were cat-sized

An international team of researchers has identified the first fossils of a newborn Tyrannosaurus rex, revealing that the apex predator began its life at a size comparable to a small cat. The discovery, published in the journal Biology, was made possible by analyzing a tiny metatarsal bone found in the Frenchman Formation in Saskatchewan, Canada.

The fossil, currently held at the Royal Saskatchewan Museum, belonged to an animal less than a year old. Researchers estimate the specimen weighed approximately 2.5 kilograms at the time of death, with an estimated hatching weight of around 1.6 kilograms. The findings suggest that even at this early stage, the juvenile possessed long legs and teeth that had already begun to function, potentially indicating they were capable of hunting shortly after hatching.

In addition to the T. rex remains, the study includes fossils of a Gorgosaurus libratus, an older relative of the T. rex. These represent the earliest known fossils of tyrannosaurids immediately after hatching. The key specimen was identified by Nicholas Longrich, a paleontologist from the University of Bath, within the T. rex Discovery Centre collection.