RALEIGH, N.C., March 15 (UPI) -- Currently, paleontologists have no tried and true method for differentiating male and female dinosaur remains, but researchers are hoping the bones of a pregnant Tyrannosaurus rex can change that.

The 68-million-year-old fossil was first discovered by a team of researchers from North Carolina State University and the North Carolina Museum of Natural Sciences in 2005, but only recently were researchers able to confirm the fossil contains a sex-specific reproductive tissue called medullary bone.


Scientists hope further analysis of the medullary bone can illuminate the evolution of egg laying in modern birds as well as offer a strategy for dinosaur sex-typing.

Medullary bone is only found in female birds; it is synthesized for the purpose of egg-laying. Theropod dinosaurs like T. rex and other scaled relatives of modern birds also laid eggs.

Because certain bone diseases found in birds can mimic medullary bone, researchers had to develop a chemical test to confirm the presence of the egg-laying bone in the T. rex. Keratan sulfate is unique to medullary bone, and researchers were able to locate its presence in the pregnant dino fossil.

"This analysis allows us to determine the gender of this fossil, and gives us a window into the evolution of egg laying in modern birds," lead study author Mary Schweitzer, a paleontologist at N.C. State, said in a news release.

The findings, detailed in the journal Scientific Reports, have paved the way for a litmus test capable of identifying pregnant female dinosaurs.

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"It's a dirty secret, but we know next to nothing about sex-linked traits in extinct dinosaurs," study co-author Lindsay Zanno explained. "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."

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