Paleontologists at North Carolina State University have determined that a 68 million year-old Tyrannosaurus Rex fossil from Montana is that of a young female, and that she was producing eggs when she died.
The proof, they say, is in the bones.
In a case of a literal "lucky break," the scientists discovered unusual bone tissue lining the hollow cavity of the T. rex's broken leg bone. In a paper published in the June 3 issue of the journal Science, Dr. Mary Schweitzer, assistant professor of paleontology with a joint appointment at the N.C. Museum of Natural Sciences, and her technician, Jennifer Wittmeyer, along with colleagues at Montana State University, share their findings and say that the presence of this particular tissue provides evidence of the dinosaur's gender and a connection between the extinct giants and living birds, specifically ostriches and emus.
Schweitzer believes that the unusual tissue inside the T. rex bone is actually medullary bone: a thin layer of highly vascular bone that is found in present-day female birds only during ovulation. This estrogen-linked reproductive bone tissue is laid down inside the hollow leg bones of the birds and persists until the last egg is laid, at which time it is completely resorbed into the bird's body. Its formation is triggered by an increase in estrogen levels, and the temporary tissue provides the calcium necessary to form eggshells. Medullary bone is only found in present-day female birds; no other egg-laying species including crocodiles, the other living dinosaur relative produces this tissue naturally.
Because the dinosaur tissues didn't look exactly like pictures published of medullary bone in living birds like chicken and quail, Schweitzer's team compared the tissue from the femur of the T. rex to that taken from leg bones of more primitive ratites, or flightless birds, such as ostriches and emus. These birds share more features
Contact: Tracey Peake
North Carolina State University