Researchers from the University of California, Davis have discovered the first fossil of an amphibious ichthyosaur in China and claims that the remains of this creature could bridge the longtime gap in the fossil records.
Scientists have long known that the ichthyosaurs, large dolphin-like marine reptiles that lived on Earth between 250 million and 90 million years ago, were the descendants of terrestrial reptiles, but there is one problem: no fossil had been found of a transitional creature that was capable of living in both land and water.
The fossil that UCD earth and planetary sciences professor Ryosuke Motani and colleagues discovered, however, is that of an ichthyosaur which appeared to have no problem adapting in land and water. Although the creature called "Cartorhynchus lenticarpus," spent most of its time in the water when it lived on Earth 248 million years ago, it had flexible flippers that allowed it to move around on land.
Ichthyosaurs were marine animals and did not have such flippers. Thus, the researchers hailed the fossil, which was found in China's Anhui Province and measures about 1.5 feet in length, to be the missing piece in the early evolution of the ichthyosaurs, which were among the dominant groups of marine reptiles in prehistoric times. The fossil is believed to be from the Triassic period.
"Cartorhynchus represents a stage of the land-to-sea transition that was somehow lacking in the fossil record of the ichthyosaur lineage, while known in most other marine reptile and mammal lineages," Motani said. "This is particularly important because some creationists tried to use ichthyosaurs as a counter-example against Darwinian evolution since the group lacked this record."
The creature also had other physical features that are unlike those of the sea-based ichthyosaurs. Besides their large flippers that give them the ability to move about on land in a seal-like movement, the animal had flexible wrists that were vital for it to crawl on land. The fossil also reveals that the creature had nose as short as those of terrestrial reptiles which is unlike the long and beak-like snouts found in most ichthyosaurs.
"We describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits," the researchers wrote in their study, which was published in the journal Nature on Nov. 5. "It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk."