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How Big Were Baby Tyrannosaurs? About the Size Of A Border Collie Dog, Study Finds

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Rachael Funnell

author

Rachael Funnell

Writer & Senior Digital Producer

Rachael is a writer and digital content producer at IFLScience with a Zoology degree from the University of Southampton, UK, and a nose for novelty animal stories.

Writer & Senior Digital Producer

baby tyrannosaur

An adorable illustration of a juvenile Tyrannosaur. Image credit: Julius Csotonyi

You don’t need to have seen a Tyrannosaurus to know they weren't something you’d want to find yourself in front of, but a new study published in the journal Canadian Journal of Earth Sciences has revealed that, like apex predators alive today, they didn’t start life at their full, terrifying potential. The research looked at fossil remains of Tyrannosaur embryos to estimate the size of their eggs and found that newborn tyrannosaurs were probably about the size of a Border Collie dog when they took their first steps.

The specimens examined in the study are the first-known fossils of Tyrannosaurus embryos ever to be identified. As such, they offered a rare opportunity to shed light on the early stages of a tyrannosaur’s life, how they developed, and even the likelihood of finding more fossilized embryonic specimens.

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A team of palaeontologists made 3D scans of delicate, fossilized remains including a tiny jaw bone and claw that were found in Canada and the United States. This information made it possible to identify the fragments as belonging to a baby Tyrannosaur. Scientists are able to scale up the size of animals from small fragments including teeth (the same has been done for Megalodon) and it’s thought the owners of these Tyrannosaur fragments would have been just under a meter (3 feet) long when they hatched. Their eggs have yet to be found in the fossil record, but the researchers estimate these would have been around 43.2 centimeters (17 inches long). Having an estimate for the lengths of these could aid their discovery in the future.

"These bones are the first window into the early lives of tyrannosaurs and they teach us about the size and appearance of baby tyrannosaurs,” said Dr Greg Funston of the University of Edinburgh's School of GeoSciences, who led the study, in a statement. “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."

how big was a baby tyrannosaur
Diagram shows the size of a baby T. rex relative to the study author. Image credit: Greg Funston

Tyrannosaurs walked the Earth around 70 million years ago in the Late Cretaceous and at their peak weighed around 8,000 kilograms (17,640 pounds or 8 tons), growing to lengths of around 12.2 meters (40 feet). The colossal animals were fierce predators in their prime, with serrated teeth made for tearing flesh and large, powerful jaws. Evidence of this bloodthirsty lifestyle has been found in the form of its teeth embedded in prey specimens (they may have even been cannibals), while their fossilized droppings have been found to contain bone fragments of Edmontosaurus and Triceratops.

But boy, were their babies apparently cute.


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