They probably cared for their offspring and may even have lived in large social groups, like modern-day whales. Plesiosaurs were reptiles, which as a group tend to lay eggs rather than giving birth.

Plesiosaurs — giant marine reptiles that ruled the oceans 75 million years ago — gave birth to single large babies and may even have nurtured their young, according to a new study. F.

In 1987, Charles Bonner discovered the fossilised bones of a large sea reptile on his family ranch. It was a flipper-limbed plesiosaur, probably Polycotylus, and one of many such fossils recovered ...

Among them was the fearsome plesiosaur, a marine reptile with a long neck and four large flippers that ruled the ancient seas. However, their unique body structure has puzzled researchers for decades.

The finding, detailed in this week's issue of the journal Science, is the first proof that plesiosaurs were viviparous—that they gave birth to live young. "The fetus is too large to make an egg ...