Scientists say a unique fossil specimen on display at the Natural History Museum of Los Angeles County shows the fossil of an embryonic plesiosaur contained within the fossil of its marine reptile mother.
"Scientists have long known that the bodies of plesiosaurs were not well suited to climbing onto land and laying eggs in a nest," Robin O'Keefe of Marshall University in West Virginia said.
"So the lack of evidence of live birth in plesiosaurs has been puzzling. This fossil documents live birth in plesiosaurs for the first time, and so finally resolves this mystery," he said Thursday in a NHM release.
The embryo is large in relation to the mother, he said.
"Many of the animals alive today that give birth to large, single young are social and have maternal care," O'Keefe said. "We speculate that plesiosaurs may have exhibited similar behaviors, making their social lives more similar to those of modern dolphins than other reptiles."
Plesiosaurs have no known living relatives but were common in the world's oceans during the age of dinosaurs.