A fossil of a newly discovered species of ancient marine reptile offers scientists a hint that evolution after the Earth's worst known mass extinction event may have occurred faster than previously thought.

It is earlier believed that marine reptiles evolved slowly after the mass extinction that wiped out about 96 percent of marine species largely because of climate change, rising sea levels and volcanic eruptions.

The discovery of the fossil of a new species of ichthyosaur casts doubts into this theory, albeit it showed the ability of life to respond to massive environmental pressures following mass extinction events.

In a study, which was published in the journal Scientific Reports on May 23, paleontologists described the Sclerocormus parviceps, an early ichthyosaur, marine animals with dolphin-like forms that lived at the same time as the earliest dinosaurs.

The discovery of this marine reptile suggests that ichthyosaurs and their relatives underwent rapid evolution and diversification within the first million years of their evolution during the early Triassic. This does not go well with what researchers previously believed to have happened over a course of millions of years.

"It now appears that ichthyosauriforms evolved rapidly within the first one million years of their evolution, in the Spathian (Early Triassic), and their true diversity has yet to be fully uncovered," the researchers wrote.

Most of the ichthyosaur species that scientists know of are marked by long beak-like snouts, streamlined bodies and tail fins. With its short snout and a whip-like tail without fins, though, the Sclerocormus defies what it takes when it comes to what an ichthyosaur should look like.

It is also toothless unlike other ichthyosaurs, which had conical teeth that they use to capture their prey. Sclerocormus appeared to have sucked up its food using its short snout.

Olivier Rieppel, from The Field Museum in Chicago, said that the characteristics of the ancient reptile showed evidence of how evolution occurred following the mass extinction that happened 250 million years ago.

"Darwin's model of evolution consists of small, gradual changes over a long period of time, and that's not quite what we're seeing here," said Rieppel. "These ichthyosauriforms seem to have evolved very quickly, in short bursts of lots of change, in leaps and bounds."

A study published in the journal Nature Communications in March revealed that climate change contributed to the extinction of the ichthyosaur.