Climate change is behind wiping out ichthyosaurs, marine reptiles that were the rulers of the oceans for 157 million years, as suggested by a study of fossils.

Some 30 million years back, the dolphin-like animal died prior to the mass dinosaur extinction towards the end of the Cretaceous period, 66 million years back.

Vertebrate paleontologist Dr. Valentin Fischer, who headed the research, said that the extinction of ichthyosaurs, which were quite familiar to oceanic life, has been a long-standing enigma. The research has recently appeared in journal Nature Communications.

Dr. Fischer of the University of Oxford said that numerous hypotheses have been proposed previously to explain the disappearance of ancient marine reptiles, including more competition from other marine reptiles and fish and the shortfall of their main food source, squid-like belemnites.

With the passage of time, these pressures would have led to decline in species diversity, letting comparatively small events to tip them into extinction.

He said, “These theories were at odds with the recent understanding of the ichthyosaur fossil record, which suggests they were actually quite diverse prior to their extinction. We wanted to analyse this extinction thoroughly and look for possible alternative drivers”.

Researchers examined teeth from museum collections and numerous recently found fossils from Russia. Thereafter, they looked for a relation between their results and geological evidence of sea surface temperatures and other environmental indicators for reaching on estimation about ichthyosaur diversity during a 150-million year time period.

Dr. Fischer said that they have discovered that they were really quite diverse in the last phase of their reign. He said that thus, their extinction was a profound, rather unexpected, happening in the history of a successful group.

Instead, their decline was linked to powerful fluctuations in sea levels and temperatures during the Cenomanian stage of the upper Cretaceous period, which was nearly 100 million to 94 million years back.

Dr. Fischer mentioned that the events coincided with intense climatic changes, such as fast-moving continents, severe volcanism, ice-free poles and anoxia episodes on the sea floor.