Scientists Identify Dinosaur Gender Through Bone Tissue

Scientists identify dinosaur gender through bone tissue

LOS ANGELES, June 2 (Xinhua) — By comparing bone tissue of the Tyrannosaurus Rex (T. rex) fossil with that of living birds, scientists said Thursday that they have found a way to identify the gender of the extinct mighty dinosaurs.

A 68-million-year-old Tyrannosaurus Rex (T. Rex) fossil is that of a young female, and she was producing eggs when she died, Mary Schweitzer, an assistant professor at North Carolina State University, and colleagues concluded in the June 3 issue of the journal Science.

Scientists discovered unusual bone tissue lining the hollow cavity of the T. rex’s broken leg bone. They said 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.

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, then 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 dinosaurs’ relative crocodiles, 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, the researchers 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 with dinosaurs than other present- day birds. They selected an ostrich and an emu in different stages of their laying cycles, when medullary bone is present.

Schweitzer viewed the tissues under both a light and an electron microscope, and found that the dinosaur tissues were virtually identical to those of the modern birds in form, location and distribution.

Demineralization of the samples revealed that the medullary bone from the ostrich and emu was virtually identical in structure, orientation and even color, with that seen in the T. rex.

Since only females produce medullary bone, its presence in the T. rex femur indicates that this fossil was a female, and probably one who died toward the end of her laying cycle, the researchers concluded.

From a biological perspective, the tissue provides another link between dinosaurs and living birds, scientists noted.

“The identification of medullary tissues in dinosaurs supports a closer relationship to birds than to other extant archosaurs, sheds light on reproductive strategies of nonavian theropods, and provides an objective means of gender determination in extinct dinosaurs,” they wrote in the Science paper.