(via Pregnant Plesiosaur Fossil May Shed Light on Ancient Animal’s Behavior | PBS NewsHour | PBS)
"Scientists have pieced together the first-ever fossil of a pregnant plesiosaur, a giant Mesozoic sea reptile from the Cretaceous Era, with an embryo still inside.
The animal, which roamed the seas 78-million years ago, is about 15-feet long — the length of a minibus — and bones indicate that the baby plesiosaur would have been as long as six feet when born…
The finding, published in the online edition of the journal Science on Thursday, is definitive evidence that the giant sea creature gave birth to single, live offspring, rather than laying eggs, like most reptiles, says paleontologist and lead author F. Robin O’Keefe. This reproductive behavior also indicates that the animals were gregarious social creatures that cared for their young, similar to toothed whales or dolphins, according to the paper.”