Since it was described in a specimen of T. rex, medullary bone has been the center of much attention. Medullary bone is a tissue unique to living female birds and found only during the egg-laying cycle that forms in the medullary cavity (and other spaces) inside bones. Following the first description in T. rex, many dinosaurs and even pterosaurs were described with medullary bone. However, at this time Science is unable to distinguish fossil medullary bone from other types of bone tissue with similar morphologies such as pathological bone growths. The best argument for medullary bone in Mesozoic fossils comes from two enantiornithines from China, the specimen shown here and the holotype of Avimaia(see Death by…). My team and I at the IVPP are currently working on developing techniques to help us distinguish fossil pathologies from true medullary bone.
Link to article:
Blog-entry for the NEE community: