T. Rex Hatchlings Were Cat-Sized, Not Dog-Sized: What Museum Drawer Fossils Reveal

"Going through museum collections, my colleagues and I have discovered the first remains of hatchling tyrannosaurs," Longrich announced . The find was described as "vanishingly rare" by ScienceAlert .

Revised Hatchling Size: A House Cat, Not a Dog

The T. rex hatchling bone came from an animal estimated to have weighed roughly 2.5 kilograms—about 5.5 pounds—comparable to a small house cat . The individual was likely just a few weeks to a few months old at death . This is far smaller than the dog-sized or turkey-sized hatchlings often depicted in popular media, including Jurassic Park .

Prior estimates had commonly cited hatchlings as being the size of a Border Collie (around 3 feet long) or a large turkey, based on earlier studies of tyrannosaur relatives and embryonic bones . The new direct fossil evidence revises that picture downward significantly.

Revised Egg and Clutch Size: 15 to 30 Small Eggs

Using scaling relationships between body mass and egg size, the team estimated that T. rex eggs were much smaller than previously assumed. The resulting clutch sizes were estimated at 15 to 30 eggs per nest . Larger clutches were possible, but the authors considered it unlikely that the number fell below 15 . This suggests a reproductive strategy that prioritized quantity over enormous individual egg size.

Revised Parental Care: Precocial and Independent

Perhaps the most surprising finding concerns parental behavior. Histological analysis of the hatchling bones showed no lines of arrested growth (LAGs), meaning the young grew continuously and rapidly without seasonal pauses in their earliest months . This growth pattern is consistent with precocial young—chicks that can walk, feed themselves, and flee predators shortly after hatching, much like baby chickens or ducks .

The findings suggest minimal to no prolonged parental feeding or guarding by adult tyrannosaurs . Instead, the reproductive strategy emphasized high egg numbers and low investment per offspring—more like a sea turtle than a modern bird of prey . The authors also interpreted tooth wear on the hatchlings as indicating they fed on relatively large vertebrates, further supporting the idea of independent, active hunters from a very young age .

What This Means for the Jurassic Park Image

The iconic scene of a protective adult T. rex guarding its nest and young appears to be fiction. "It turns out, Jurassic Park was wrong. Again," noted one report . While earlier research had debated the extent of tyrannosaur parental care, this study provides the first direct fossil evidence that T. rex hatchlings were largely on their own from birth .

Bottom Line

The first confirmed T. rex hatchling fossils—discovered in museum drawers—reveal that newborns were cat-sized (~2.5 kg), not dog- or turkey-sized; nests likely held 15 to 30 small eggs; and the young were precocial and largely independent from birth, contradicting the protective-parenting image popularized in films .