First fossil evidence of a pregnant T-rex
Scientists detect a characteristic signature of egg laying in bone tissue
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.