Martin, an expert on fossil marine reptiles, co-led the 2005 expedition to Antarctica that recovered the plesiosaur.

If you can imagine something which is a combination between a turtle and a sea snake, but crocodile-sized, that's just a plesiosaur. And the well-preserved fossil skeleton of a juvenile plesiosaur that roamed Southern Ocean roughly 70 million years ago has just been found in Antarctica.

A massive volcanic explosion may have killed and preserved the baby, in a far warmer Ocean than today. The fossil represents one of the most-complete plesiosaur skeletons ever found and the best-articulated fossil skeleton ever recovered from Antarctica, even if the skull has eroded away from the body.

When the creature was alive, their paddle-like fins would have allowed them to "fly through the water" in a motion very similar to modern-day penguins. "After it was prepared in the United States, the specimen was discovered tobe the 5-foot-long (1.5 meters) skeleton of a long-necked (elasmosaurid) plesiosaur. An adult specimen could reach over 32 feet (10 meters) in length. Most of the bones of the baby plesiosaur had not developed distinct ends due to the youth of the specimen", said James E. Martin, curator of vertebrate paleontology and coordinator of the paleontology program at the South Dakota School of Mines and Technology's Museum of Geology.

The animal's stomach area was spectacularly preserved, with stomach ribs (gastralia) from the abdomen, which rather than being long, straight bones like those of most plesiosaurs, are forked, sometimes into three prongs.

Numerous small, rounded stomach stones (gastroliths) were concentrated within the abdominal cavity, being ingested even by juvenile plesiosaurs to help maintain buoyancy or to aid digestion. Extreme weather at the excavation site on 650 feet (200 m) elevation on Vega Island off the Antarctic Peninsula, including over 70 miles (120 km) an hour winds, icy temperatures and frozen ground, and lack of field time impeded further exploration for the eroded skull.

Volcanic ash beds were layered within the shallow marine sands at the site, suggesting a major eruption. Even more, silica released from the ash permitted spectacular preservation of the skeleton. The bones were associated with marine shellfish that pointed the area was a shallow-water marine environment 70 million years ago. There were also found very advanced shore birds from the same period.

Since 1998, the American-Argentine team have found numerous isolated elements of juvenile plesiosaurs and mosasaurs, giant marine reptiles that were in fact huge monitor lizards with fins.

The scientists think the site may have been a shallow-water area of birthing and nursery where the young remained until they were of sufficient size and ability to survive in open waters. Whether plesiosaurs gave live birth has not been proved (even if ichthyosaurs, another ancient marine reptile group were viviparous) but numerous bones and partial skeletons of larger plesiosaurs were found in the same area as the young. The juvenile plesiosaur seems to be related to one found in New Zealand in 1874 and named Mauisaurus, characterized by a rounded end of the major paddle bone. Mauisaurus may have been confined to the southern oceans where it lived more than 5 million years.

Image credit: Nicolle Rager, National Science Fundation