Quirks & Quarks

First fossil evidence of a pregnant T-rex

Scientists detect a characteristic signature of bone that stores calcium for egg laying

Scientists detect a characteristic signature of egg laying in bone tissue

Tyrannosaurs Rex fossil cast at the Royal Tyrell Museum (Pierre Camateros, cc-by-sa-3.0)
It has always been difficult to determine the sex of dinosaurs from the fossil record. The overall skeletal anatomy of male and female dinosaurs is almost identical. But a recent study by Dr. Mary Higby Schweitzer, a Professor in the Department of Biological Sciences at North Carolina State University, has confirmed that a 68-million-year-old T-rex, found in 2005, is, in fact, female and pregnant.

She and her team found medullary bone tissue in the dinosaur's femur. Medullary bone is found in modern female birds that are in the process of preparing to lay eggs. It is distinct in both its chemical composition and molecular structure from other bone.

Because birds are the modern relatives of dinosaurs, scientists assume medullary bone served the same purpose in T-rex. They hope that this discovery will help determine the sex of other Tyrannosaur fossils.     

Related Links

Paper in Nature Scientific Reports
- North Carolina State University release
- CBC News story
- National Geographic blog
- Washington Post story