This particular team hails from the North Carolina State University and the North Carolina Museum of Natural Sciences, where they have already published their findings. Lead author Mary Schweitzer said, “This analysis allows us to determine the gender of this fossil, and gives us a window into the evolution of egg-laying in modern birds.”
In this particular fossil, it carries a kind of tissue — medullary bone — which is normally found in female birds that happen to carry eggs, or are just done laying them. With theropod dinosaurs such as the T. rex theorized to evolve into modern-day birds, extrapolating modern information into the past makes logical sense. Schweitzer continued, “All the evidence we had at the time pointed to this tissue being medullary bone. But there are some bone diseases that occur in birds, like osteopetrosis, that can mimic the appearance of medullary bone under the microscope. So to be sure, we needed to do chemical analysis of the tissue.”