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How to tell if a T. rex is expecting

Chemical test of fossil detects a kind of estrogen-fueled bone that’s also found in egg-producing female birds

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6:00am, March 18, 2016
T. rex and bone

IT’S A GIRL  New chemical analyses can reveal whether a T. rex was “pregnant,” and thus female, by detecting the presence of loosely woven “medullary bone” (light colored material in inset picture) inside a fossilized bone.

Call it a T. rex pregnancy test.

Chemical analyses of fingernail-sized slivers of bone can reveal whether a Tyrannosaurus rex was expecting, paleontologist Mary Schweitzer of North Carolina State University in Raleigh and colleagues report March 15 in Scientific Reports.

The analyses confirm that T. rex had medullary bone, a type of reproductive tissue found in female birds, but only when they’re producing eggs, or “in lay.” Scientists had hypothesized that dinosaurs might have this tissue, too, and in 2005 Schweitzer’s team spotted what looked like medullary bone in a 70-million-year-old T. rex fossil found in Montana (the dino was about 18 years old when it died).

A colleague had sent Schweitzer a box filled with the dinosaur’s bones, she says. “I pulled the first fragment out and said, ‘Oh my gosh! It’s a girl and it

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