A pregnant T. rex, which lived 68 million years ago in Montana, was recently confirmed by researchers from North Carolina State University and the North Carolina Museum of Natural Sciences and could shed new light on the evolution of egg-laying in modern birds.
Researchers, whose work was documented in a study
published online Tuesday in the science journal Nature, said they were able to identify the presence of medullary bone, a gender-specific reproductive tissue, in a fossilized Tyrannosaurus rex femur,
according to a statement from North Carolina State University.
The statement said that medullary bone is only found in female birds and only during the period before or during egg-laying.
"All the evidence we had at the time pointed to this tissue being medullary bone," Mary Schweitzer, the lead author of the study and a paleontologist with North Carolina State, said in the university's statement.
"But there are some bone diseases that occur in birds, like osteopetrosis, that can mimic the appearance of medullary bone under the microscope. So to be sure we needed to do chemical analysis of the tissue," she continued.
Researchers were able to confirm that tissue was indeed medullary bone by testing for keratin sulfate using monoclonal antibodies. They then compared the results to the same tests performed on known medullary tissue from ostrich and chicken bone.
The Washington Post said it will be difficult for researchers to find more medullary bone since the tissue was present for such a brief time in dinosaurs and not all scientists are comfortable with cracking open fossils to do the research needed.
Yet, Lindsay Zanno, a North Carolina Museum of Natural Sciences paleontologist, said there needs to be a concerted effort to find more since they now have a chemical fingerprint.
"It's a dirty secret, but we know next to nothing about sex-linked traits in extinct dinosaurs," Zanno said in the university statement. "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."