An international team of researchers claim they have the missing link between a prehistoric aquatic predator and its even older land-dwelling ancestors. The fossil has a body form that suggests it exhibited amphibian-like behavior and is thought to link Ichthyosaurs to their terrestrial ancestors. The find is said to be problematic for creationists, or those who reject the prevailing naturalistic explanation for how life originated and evolved on Earth.

Paleontologists have long argued that Ichthyosaurs evolved from land-dwelling ancestors as they returned back to aquatic environments over time. However, fossils showing stages of this transition have been lacking. A new report published on Wednesday in the journal Nature describes a putative intermediate fossil of an amphibious ancestor of the water-dwelling Ichthyosaurs called Cartorhynchus lenticarpus.

“Many creationists have tried to portray ichthyosaurs as being contrary to evolution,” said lead author Ryosuke Motani, a professor of earth and planetary sciences at the University of California Davis. “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?”

Montani and collegues from around the globe found the fossil in the Anhui Province of China back in 2011 but were not certain how to classify it. The creature appears to have lived 248 million years ago and measured about 18 inches long.

“Initially I was really puzzled by this fossil,” Motani said. “I could tell it was related [to ichthyosaurs], but I didn’t know how to place it. It took me about a year before I was sure I had no doubts.”

Because the fossil shows signs of neither adaptation to aquatic nor terrestrial life, the researchers concluded it must be of an amphibious creature. The bones and flippers of this fossil suggest time spent on both land and in water during a period roughly four million years after a mass extinction of dinosaurs.

“This animal probably had a happy life. It was in the tropics, and it was probably a bottom feeder that fed on soft-bodied things like squid and animals like shrimp,” Motani said. “And for a predator like that to exist, there has to be plenty of prey. This was probably one of the first predators to appear after that extinction.”