The remains of a pregnant Tyrannosaurus rex that had died in ancient Montana about 68 million years ago may provide hints into how to identify male and female theropods, or bipedal meat-eating dinosaurs.

In a new study, researchers said they looked at the organic components in the dinosaur’s bone structure and after verify details of the fossil, reached at the conclusion that the T. rex was pregnant. The bone structure had survived for tens of millions of years since the predator’s death.

Mary Schweitzer, an evolutionary biologist at North Carolina State University and study lead researcher, said the T. rex was discovered in 2000 by Bob Harmon, a paleontologist at the Museum of the Rockies in Montana, Hell Creek Formation.

Schweitzer said Harmon sat down in dinosaur territory and one day unexpectedly felt a fossil behind his back. Harmon immediately shared the information with his team members and colleagues and all of them spent the next three years digging out the enormous specimen.

Schweitzer said in a statement: “We need to quit selling fossils short. They have a lot more information in them than we would think of [finding in] 65-million-year-old bone… 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. I think good scientists should always be second-guessing themselves".

Eleven years ago, the team had published a study in the journal Science, which claimed that the fossil contained medullary bone that is a kind of bone that has extra calcium deposits and the organic compound keratan sulfate that are believed to help female creatures lay eggs.

Medullary bone is present only during the egg-laying process and just before it. Schweitzer said its occurrence in the fossils suggested that the T. rex was pregnant.