Soft tissue, amazingly found surviving in a hollow cavity of a 68 million-year-old Tyrannosaurus rex dinosaur leg bone fossil has revealed that the ancient creature was a young female that was producing eggs when she died in what is now Montana.
National Science Foundation paleontologists at the North Carolina Museum of Natural Sciences stated in a press release that the presence of this particular tissue provides evidence of the dinosaur's gender, and a connection between dinosaurs and present-day birds.
Scientists believe the tissue is "medullary bone," a type of tissue found in present-day female birds only during ovulation. The tissue forms inside the birds' hollow leg bones and persists until the last egg is laid, at which time it is completely reabsorbed into the bird's body. The tissue provides calcium needed to produce eggshells.
"The discovery of medullary bone in T. rex is important because it allows us to figure out the gender of a dinosaur," said NSF scientist Mary Schweitzer in a press release. "It also adds to the support linking birds and dinosaurs, and shows that their reproductive physiologies may have been similar. We hope to be able to identify features in dinosaurs that will help determine the gender of other fossils, and lead to information about their herd structure or family groups."
Medullary bone is only found in present-day female birds; no other egg-laying species (including crocodiles, the other living dinosaur relative) produces the tissue naturally.
"Schweitzer's recognition of medullary tissues in T. rex is very important because it indicates a close relationship between dinosaurs and birds," said Enriqueta Barrera, program director in the National Science Foundation (NSF)'s earth sciences division, which funded the research. "Birds and dinosaurs may have mobilized calcium and shelled their eggs in a similar manner. The discovery also provides us with the means to identify gender in dinosaurs."
Schweitzer found that the dinosaur tissue was virtually identical to that of the modern birds in form, location and distribution. Removal of the bones' minerals revealed that medullary bone from the ostrich and emu was virtually identical in structure, orientation and even color, with that of the T. rex.
[Source: National Science Foundation]