Pregnant T. Rex Unearthed

(CNN)Through the years of searching for fossils of the ever-popular Tyrannosaurus rex, locating a pregnant one has been understandably difficult.

But scientists now believe they've located one, determining this particular T. rex that roamed Montana was female.

Traditionally, it's been extraordinarily difficult to figure out a dinosaur fossil's gender.

Specifically, the researchers from North Carolina State University and the North Carolina Museum of Natural Sciences found a medullary bone in a T. rex femur.

These bones are found only in female birds in the period before or during egg-laying.

Now, the scientists believe they will be able to find differences between male and female dinosaurs of this kind (theropod dinosaurs), and learn more about the evolution of egg-laying in birds.

"It's a dirty secret, but we know next to nothing about sex-linked traits in extinct dinosaurs. Dinosaurs weren't shy about sexual signaling, all those bells and whistles, horns, crests, and frills, and yet we just haven't had a reliable way to tell males from females," said Lindsay Zanno, a Museum of Natural Sciences paleontologist, in a press release.

"Just being able to identify a dinosaur definitively as a female opens up a whole new world of possibilities. Now that we can show pregnant dinosaurs have a chemical fingerprint, we need a concerted effort to find more."

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