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Bone Test Confirms T. rex Was Pregnant

(Image:  pixabay/  CC0 1.0)

A pregnant Tyrannosaurus rex died around 68 million years ago, and may just be the key to gender differences between theropod or meat-eating dinosaur species. It could also give some insight into the evolution of egg laying in modern birds.

Researchers from North Carolina State University and the North Carolina Museum of Natural Sciences have confirmed the presence of medullary bone — a gender-specific reproductive tissue — in a fossilized T. rex femur.

Paleontologist, Bob Harmon from the Museum of the Rockies in Montana, discovered the T. rex in Hell Creek Formation back in 2000. While exploring the dinosaur territory he sat down, and then felt a fossil behind his back. Harmon then shared his news with his colleagues, where they then spent the next three years excavating the enormous specimen, according to live science.

Medullary bone is only found during the period before or during egg laying, and is chemically different from other bone types. According to an NC State University statement:

Mary Schweitzer, an NC State paleontologist with a joint appointment at the NC Museum of Natural Sciences and the lead author of the paper published in journal, Scientific Reports, made the discovery of what she believed to be medullary bone in the femur of the 68 million year old T. rex fossil in 2005. Schweitzer explains:

A substance called keratan sulfate is only present in medullary bone, however, it was believed that the original chemistry of dinosaur bone could not survive millions of years.

Transverse section of MOR 1125 whole femur, showing almost complete infilling of the medullary cavity with MB. No gross deformation (corresponding to fracture callus) or bony expansion (corresponding to osteopetrosis) can be seen. Red line marks boundary between dense cortical bone and endosteal lamellar bone penetrated by multiple erosion rooms. Erosion rooms can be seen extending deep into the cortex in one region of the bone.

Transverse section of MOR 1125 whole femur, showing almost complete infilling of the medullary cavity with MB. No gross deformation (corresponding to fracture callus) or bony expansion (corresponding to osteopetrosis) can be seen. Red line marks boundary between dense cortical bone and endosteal lamellar bone penetrated by multiple erosion rooms. Erosion rooms can be seen extending deep into the cortex in one region of the bone. (Image: Scientific Reports)

But this has now been put into question; while Schweitzer and her colleagues were conducting a number of different tests on the T. rex sample, one of which tested for keratan sulfate using monoclonal antibodies. When they compared their results to tests performed on known medullary tissue from ostrich and chicken bone, it was confirmed that the tissue from the T. rex was medullary bone.

Schweitzer said in a statement:

Schweitzer recognizes while most paleontologists would not cut open or demineralize their fossils to search for rare medullary bone, the femur of MOR 1125 (the sample name) was already broken when it arrived to Schweitzer. Lindsay Zanno, co-author from N.C. Museum of Natural Sciences paleontologist with a joint appointment at NC State, has shown by a CT scan of the fossils it could help in narrowing down the search.

Zanno explained in a statement:

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