First-known foot bone of a baby T. rex found stashed in pile of fossils after being mistakenly identified

The discovery of a tiny baby Tyrannosaurus rex foot bone gave researchers insight into what T. rex reproduction looked like, from how big a clutch of eggs was to how large the T. rex hatchlings were.

Nick Longrich, a paleontologist and evolutionary biologist at the University of Bath in England, along with other researchers, made this discovery while going through collections of small dinosaur bones that were tucked away and typically misidentified. 

In a video posted to his YouTube page, Longrich described how he stumbled upon such a rare find, saying he couldn't make sense of a third metatarsal or foot bone of what was believed to be a theropod dinosaur. 

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Longrich said this bone varied in appearance from other theropod bones he'd seen in the past, and determined it wasn't from a number of species of dinosaur. 

"It doesn't match anything I've seen before," Longrich said, as he described the discovery. "It just didn't seem to fit in any of the categories." 

He said upon taking a closer look at the bone, he noticed its texture, which was porous and typical of an immature dinosaur. 

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Eventually, the bone was identified as that of a hatchling T. rex. 

"By process of elimination, this is the foot bone of a very, very tiny T. rex," Longrich said. "This is the smallest T. rex that we've ever seen." 

This little bitty bone helped Longrich and his research partners figure out a whole host of information about these tiny hatchlings, information which was published in the journal Biology. 

Researchers discovered that hatchling T. rex's were very small, likely no bigger than a small cat, Longrich said. 

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Additionally, they theorized that baby T. rex's moved quickly after hatching, much like modern day chickens or crocodiles. 

Evidence suggests that these babies would be protected by their parents, but in general, the babies would seek their own food and receive little care from their parents otherwise. 

The study also revealed that T. rex egg clutches were likely very large, with somewhere between 15 and 30 eggs per clutch, with the chance of between 50 and 100 eggs in a clutch also possible. 

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Longrich said dozens of eggs were likely, but the mortality rate was also likely incredibly high. 

The bone marks an important discovery for scientists and paleontologists who are working to learn more about the dinosaurs, how they lived and the evolution of the extinct species.