August 12, 2011

Scientists Discover Live Birth For Plesiosaurs

According to a paper to be published on August 12, 2011, in Science magazine, researchers discovered that the fossilized remains of a large aquatic dinosaur reveal the creature gave birth to live young, rather than laying eggs.

The Natural History Museum of Los Angeles County contains a 15.4 foot-long adult specimen of a Polycotylus latippinus, a large, carnivorous sea reptile known as a plesiosaur. This particular specimen shows a complete, developing embryonic skeleton within the skeleton of the mother. This is the first evidence that plesiosaur gave birth live to its young, may have lived in social groups and engaged in parental care.

The researchers, Dr. F. Robin O'Keefe and Luis Chiappe have also determined that plesiosaurs were unique among aquatic reptiles in giving birth to large, live young.

"Scientists have long known that the bodies of plesiosaurs were not well suited to climbing onto land and laying eggs in a nest," Dr. O'Keefe stated. "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. Also the embryo is very large in comparison to the mother, much larger than one would expect in comparison with other reptile. Many of the animals alive today that give birth  to large, single young are social and have maternal care. We speculate that plesiosaurs may have exhibited similar behaviors, making their social lives more similar to those of modern dolphins than other reptiles."

The fossil was first discovered in 1987 by Charles Bonner at the Bonner Ranch in Logan County, Kansas and has been preserved by the NHM and mounted for display. It is nearly complete except for parts of the adult's neck and skull. The fossil has been dated to between 72 million and 78 million years ago.

In their paper, O'Keefe and Chiappe suggest a parallel between plesiosaurs and modern whales, also large animals that give birth to relatively big offspring. Like whales, they said, plesiosaurs may have formed social groups and tended their young.

Image Credit: S. Abramowicz, Dinosaur Institute, NHM


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