Researchers say they've discovered a missing link between an ancient dolphin-like aquatic predator and some ancestors that lived on land.

Known as Ichthyosaurs, the reptiles that lived in the world's seas in  the time of the dinosaurs evolved from land creatures that returned to the water over a long period of time, scientists say.

Although paleontologists had long suspected a lineage existed between the land creatures and their ocean-going descendants, the fossil record had been unclear -- until now.

The clear link -- the until-now missing stage in the ichthyosaurs' evolution -- was found in China in 2011 by a team led by researchers at the University of California, Davis, and dubbed Cartorhynchus lenticarpus, the university reported.

Before the discovery in China's Anhui Province, there had been no fossil evidence for their transition from the land to the sea.

"But now we have this fossil showing the transition," says lead study author Ryosuke Motani, a UC Davis professor of earth and planetary sciences.

And rather than strictly terrestrial or marine, the creature was a true amphibian, Motani says.

Unlike later ichthyosaurs completely adapted to a life at sea, it possessed unusually large and flexible flippers, like a modern-day seal, with flexible wrists that would have allowed it to crawl on the ground.

"There's nothing that prevents it from coming onto land," says Motani of the 248-million-year-old fossil.

An amphibious animal as an intermediary would make sense in a transition between land and sea but had been missing from the ichthyosaur fossil record.

The fossil in China fits the picture "very nicely," he says. 

The discovery could be a problems for creationists who've tried to suggests the creatures' developing "backward" from land animals to sea creatures somehow disproves evolution, Motani says.

"Many creationists have tried to portray ichthyosaurs as being contrary to evolution," he says. "We knew based on their bone structure that they were reptiles, and that their ancestors lived on land at some time, but they were fully adapted to life in the water. So creationists would say, well, they couldn't have evolved from those reptiles, because where's the link?"

Now the link -- in the form of the foot-and-a-half-long fossil from China -- has been found, filling the evolutionary "gap" of the fossil record, he says.

Motani adds that he hopes to find more fossils that will improve the record, and he's in search of the direct ancestor of Cartorhynchus lenticarpus, which would have also been amphibious but spending a bit more of its time on land.

"We're looking for that one now," he says.