An ancient marine reptile that swam the oceans nearly 250 million years ago had unusual pebble-like teeth which it used to crush hard-shelled prey, scientists believe.
The creature, named Cartorhynchus lenticarpus, belongs to an extinct group of reptiles known as ichthyosaurs.
Not much is known about the ancestry of these animals but experts believe they may be "more closely related to crocodiles and dinosaurs and birds than they are to lizards and snakes".
Olivier Rieppel, a palaeontologist at the Field Museum in Chicago, and one of the study authors, said: "By studying this early ichthyosaur's unusual rounded teeth, we get a better understanding of how these animals evolved and what their lifestyles were like."
At 1.5 foot long, Cartorhynchus is the smallest known ichthyosaur and may have lived on land and in the sea.
Its fossil remains found in Anhui province, China, date from the start of the Triassic period about 248 million years ago. While scanning the fossil, scientists discovered unusual pebble-like teeth hidden in its short snout, with signs of wear and tear.
The teeth may have been used for crushing the shells of snails and clam-like molluscs known as bivalves, the researchers, whose findings can be found in the 'Scientific Reports' journal, said.
As well as big flippers, Cartorhynchus had flexible wrists for movement on the ground.
Cartorhynchus lived about four million years after the worst mass extinction in history, known as the Permian-Triassic extinction, which wiped out 96pc of species and may have been linked to global warming.
Mr Rieppel said: "There were no marine reptiles prior to the Triassic. That's what makes these early ichthyosaurs so interesting - they tell us about the recovery from the mass extinction, because they entered the sea only after it.
"By gaining a better understanding of how they evolved, we get a better sense of how life rebounds after extinctions."