Probably the world's most famous family of dinosaurs, the tyrannosaurs included the 40-ft (12-m) Tyrannosaurus rex within their ranks. Newly studied fossils now suggest that the reptiles were about "the size of a border collie" when first hatching from the egg.
The research was conducted by a team of scientists who are all affiliated with both Scotland's University of Edinburgh and Canada's University of Alberta.
They performed 3D scans of a 3-cm (1.2-in) section of jawbone from an embryonic Daspletosaurus tyrannosaur – found in Montana's Two Medicine Formation – along with a claw most likely from an embryonic Albertosaurus tyrannosaur, found in Alberta's Horseshoe Canyon Formation.
The jawbone exhibited a number of tyrannosaur-specific features, such as a pronounced "chin." Its teeth were just beginning to develop, indicating that the individual was indeed a baby.
Based on the measurements of the specimens, it was estimated that the dinosaurs couldn't have been any larger than 3 feet (0.9 m) in length upon hatching. It was additionally determined that the eggs they were curled up inside of were approximately 17 inches long (432 mm) – this is a significant discovery, as paleontologists have yet to find fossilized eggs that they know for a fact are those of a tyrannosaur.
"These bones are the first window into the early lives of tyrannosaurs and they teach us about the size and appearance of baby tyrannosaurs," says U Edinburgh's Dr. Greg Funston, who led the study. "We now know that they would have been the largest hatchlings to ever emerge from eggs, and they would have looked remarkably like their parents – both good signs for finding more material in the future."
A paper on the research was recently published in the Canadian Journal of Earth Sciences.
Source: University of Edinburgh