Plesiosaur dinosaur fossil solves breeding puzzle

From SFGate: Plesiosaur dinosaur fossil solves breeding puzzle

The fossil bones of a giant, long-necked swimming reptile from the age of the dinosaurs have resolved a long-held mystery about the animals and how they reproduced.

Those denizens of ancient seas - like modern whales and dolphins - apparently gave birth to their infants beneath the water one at a time, and could have cared for them much as modern whales do, scientists say.

The unique water-living animal, known as a plesiosaur, lived about 78 million years ago, and while fossils of many other creatures in the marine reptile world of that era show they gave birth to a dozen or more young at a time, this one is the first to show evidence of a single birth and only in the water, according to the paleontologists.

It also resolves a puzzle about the animal by showing that the tribe were uniquely sea creatures and never laid eggs on land, according to Luis Chiappe of the Dinosaur Institute at the Los Angeles Natural History Museum, and F. Robin O'Keefe of Marshall University in Huntington, W.Va.

They report their findings today in the journal Science.

The scientists say they discovered that the bones they assembled were those of a mother who was clearly pregnant.

The huge bones of the plesiosaur were first unearthed nearly 25 years ago on a Kansas ranch. The plesiosaurs were viviparous, meaning that instead of producing and hatching eggs, they gave birth to a single offspring that had developed within the mother's body. A few other ancient reptiles were also viviparous, but their fossils have shown that they produced as many as 18 or 19 babies at a time, according to Chiappe and O'Keefe.

"They've made a strong case," Glenn W. Storrs, a noted specialist on the plesiosaur animals at the Cincinnati Museum Center, said in an interview. "It's very clear that they have shown a fetus inside a mother ... and it was certainly not made for coming up on land where its body would have been crushed to death."

Chiappe and O'Keefe calculated that at the time of the animal's pregnancy she would have been about 15 feet long, and her fetus about five feet long - meaning it was probably two-thirds of the way toward birth.

Chiappe and O'Keefe likened the plesiosaurs to modern-day land reptiles like California's western skinks that "exhibit mammal-like social behaviors." The reproductive strategy of the plesiosaurs, they said, is a fine example of how evolution has led to the emergence of big animals that breed slowly.

This new evidence for the evolution of live birth in plesiosaurs, like so many other marine reptiles of the dinosaur era "leaves me nothing but spell-bound," said Michael Caldwell, a specialist at the University of Alberta. "Absolutely amazing stuff!" he said in an e-mail.

The skeleton of the ancient animal is now on exhibit at the Los Angeles museum's Dinosaur Institute where Chiappe is the director.