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A 248 million-year-old fossil of an ancient reptile found in China is the oldest known member of a well-known group of marine reptiles, and may have lived both on land and in the sea.

The specimen is a primitive type of ichthyopterygian, a group related to ichthyosaurs, which are large marine reptiles that dominated the world's oceans after the Permian-Triassic extinction. During that extinction event, which occurred 252 million years ago, up to 96 percent of marine animals and 70 percent of land animals died out. The recently discovered fossil provides new evidence that ichthyosaurs evolved from creatures that lived on land, researchers say.

"This new animal is a link between the terrestrial ancestor and the ichthyosaurs fully adapted to a life in the sea," said Da-yong Jiang, a geologist at Peking University in China and leader of the study published Wednesday by the journal Nature. [Image Gallery: Photos Reveal Prehistoric Sea Monster]

An artist's reconstruction shows the primitive ichthyopterygian known as Cartorhynchus lenticarpus, which lived 248 million years ago with possibly amphibious habits. Stefano Broccoli

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Ichthyosaurs, whose name is Greek for "fish lizard," lived from about 248 million to 95 million years ago. The group was extremely diverse, with body lengths ranging from less than 3.3 feet (1 meter) to more than 66 feet (20 meters).

Until now, all known ichthyosaur fossils came from animals that lived exclusively in the ocean, and there was a huge gap in the fossil record between them and their ancestors, Jiang told LiveScience in an email. Scientists didn't know whether their ancestors lived on land.

The new species found by Jiang and his team, which they named Cartorhynchus lenticarpus, is the smallest known ichthyosaur-type creature — only about 1.3 feet (40 centimeters) long.

A fossil specimen representing the creature known as Cartorhynchus lenticarpus is being kept at the Anhui Geological Museum in China. Ryosuke Motani

Unlike other ichthyosaurs, the new specimen has unusually large flippers that probably limited its ability to get around on land, making it resemble a modern seal. It also has a short snout and body trunk, like other land reptiles, the researchers said.

The animal was probably a suction feeder on the seafloor, and may have eaten worms or eel-like creatures called conodonts, Jiang said.

The researchers found the fossil during an excavation at Chaohu, in South China, in 2011.

— Tanya Lewis, LiveScience

This is a condensed version of a report from LiveScience. Read the full report. Follow Tanya Lewis on Twitter and Google+. Follow LiveScience on Twitter, Facebook andGoogle+.