Remember back in March when Mary Schweitzer found soft tissue inside a T. Rex bone? Back then I said that “the discovery could shed light on […] the evolutionary relationship between dinosaurs and contemporary species.” Am I a freakin’ prophet or what?

Today we learn that the unusual gross anatomy from the interior of the MOR 1125 femur was immediately recognized by Schweitzer as Medullary bone. Medullary tissue is a calcium-rich layer lining the inside of bird’s bone marrow cavities that develops during the egg-laying process. The formation of medullary tissue is today uniquely avian and distinct from reptilian egg-laying biology.

The tissue in question is also an indicator as to the gender of the specimen – since medullary tissue is created only my momma dinosaurs, any specimen that’s missing it is either male or under age. Keep your eyes open for a more detailed analysis at the Panda’s Thumb once they’ve had a chance to sift through Schweitzer et al.’s paper.