Developing baby bones found inside fossil marine skeleton

At the Natural History Museum of Los Angeles, in California scientists are learning from a skeleton that  belongs to a marine reptile known as Polycotylus (Pahl-ee-KOAT-eh-luss).

Developing baby bones found inside fossil marine skeleton

Inside the fossil skeleton, scientists found the bones of a developing baby. By comparing that fossil to other young plesiosaurs, researchers are figuring out how these animals grew.

Polycotylus is a type of plesiosaur (PLEES-ee-oh-sawr). These reptiles swam the seas between 203 million and 66 million years ago. They weren’t dinosaurs, although dinos lived at the same time. Plesiosaurs were enormous growing to 5 meters (16 feet) in length. 

Instead of laying eggs like other reptiles, a mother Polycotylus gave birth to a single, large offspring. No clues existed that plesiosaurs might have had live births. But they seemed too big to venture ashore to lay eggs.

The mystery remained unsolved until 2011. That’s when O’Keefe and his colleagues first studied the Polycotylusskeleton in Los Angeles. As luck would have it, this plesiosaur had been pregnant.

That showed scientists that Polycotylus gave birth to live young, instead of laying eggs. And it let O’Keefe compare the baby to other fossils for the new study.

“Zooming in to the actual bone cells, and seeing the direction of the bone fibers” was very important, O’Keefe says. It helped him to understand how the bones grew. And that revealed more about the ancient reptile’s life story.

Plesiosaurs, the new data show, had “an absolutely unique bone histology,” Fleischle says. It “is not comparable to any other species, living or extinct.” That’s why it’s critical to compare fossil bones to others from the same species, she says.


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