Tyrannosaurus rex hatchlings were roughly the size of small house cats, yet they were active predators that began hunting shortly after leaving the nest, according to a study published in the peer-reviewed journal Gizmodo. Researchers found that these young dinosaurs were unsafe at any size,
functioning as bone-crushing predators within their own size classes from a very early age.
Evidence from Fossilized Metatarsals
The findings are based on the analysis of the first known fossils of hatchling tyrannosaurs, including T. rex and its close cousin Gorgosaurus libratus. Paleontologist Nicholas Longrich, an evolutionary biologist at the University of Bath in the UK and the study’s lead author, discovered the metatarsals of a baby T. rex within the collection of the Royal Saskatchewan Museum’s T. rex Discovery Centre in Canada.
To analyze the bones, the team used synchrotron computed microtomography—a sophisticated version of X-ray CT scanning. This technology revealed several key details about the animal’s early life:
- Age: The scans showed no growth rings, confirming the fossil belonged to a nearly newborn animal less than a year old.
- Growth Rate: A dense, intricate web of interconnected blood vessels and bone cell spaces indicated the specimen was growing rapidly.
- Activity Level: Canals found in the bone provided evidence that the hatchlings were quickly out of the nest and running around.
Hunting Capabilities and Physical Dimensions
While the baby T. rex was small, it was lethal. Eric Snively, an Oklahoma State University anatomy professor and study co-author, stated that babies were smashing into the bones of their food, just like giant adults.
This claim is supported by fossilized teeth from the hatchlings, which exhibited thick enamel and wear and tear at the apex, consistent with the dental damage seen in adult fossils of the species.
The physical dimensions of these tyrannosaur tykes
differ from previous projections. While some earlier claims suggested they measured three feet from nose to tail, this study found they were roughly 30 inches long. They weighed approximately 5.5 pounds (2.5 kilograms)—similar to the average size of a Yorkshire terrier—and may have weighed only around 4 pounds when newly hatched.
Reproductive Strategies and Parental Care
Although a complete T. rex egg has never been identified, the research suggests these dinosaurs laid large clutches of 20 to 30 eggs, with each egg being approximately the size of a half-gallon of milk. This reproductive strategy indicates that T. rex produced large bundles of offspring rather than investing high energy into a few babies.
The study suggests a transitional style of parenting. Longrich noted that T. rex parents invested more in their offspring than turtles, lizards, or crocodilians, but were less attentive than modern mammals and birds. Snively added that there was likely some parental investment, such as guiding the young and guarding the nest, though the babies could fend for themselves shortly after hatching.
According to Snively, this research is significant because it documents the full range of size for Tyrannosaurus individuals as they grew, illustrating how they maintained similar ecosystem roles as bone-crushing predators throughout their entire lives.
Worth a look
