Discovery of giant marine reptile skull reveals new evolutionary theories |

(CNN) — The discovery of a giant marine reptile skull in the United States has revealed new theories about the speed of evolution and how quickly the process can produce diversity.

The giant ichthyosaur fossil – with a skull measuring nearly two meters (6.6ft) long, an estimated body length of over 17 meters (55.7ft) and weighing 45 tonnes – has been found in Nevada.

Ichthyosaurs are large, extinct marine reptiles that dominated the sea more than 200 million years ago. Analysis of the skull of this particular ichthyosaur fossil has revealed a new species: Cymbospondylus youngorum.

The skull analysis was part of a larger research effort undertaken by an international team to understand how quickly body size evolved in ichthyosaurs compared to how body size evolved in whales – another group originally four-legged terrestrial vertebrates that have come back to life. in the sea, just like the ichthyosaur.

A reconstruction of the life of Cymbospondylus youngorum, in a Triassic ocean teeming with life. Ammonites and squid were abundant in this open ocean environment.

ichthyosaurs grew to the size of a giant body in a very short time, evolutionarily speaking – roughly 3 million years. By comparison, whales took about 45 million years to reach their largest body size,” said Lars Schmitz, associate professor of biology in the WM Keck Science Department – the shared science department at Claremont McKenna, Pitzer and Scripps Colleges at Claremont, Calif. – said in a press release.

Schmitz is part of the team that researched the fossil.

“What this fossil discovery shows is that if the ecological conditions are right and there is some environmental stability, evolution can proceed remarkably quickly.”

Schmitz worked with a team of international researchers to analyze the fossil, identify the ichthyosaur as a new species, create a phylogenetic tree — a diagram that shows the evolutionary relationships between various biological species — and then conducted a computer analysis comparing the rate and type of change from body size of ichthyosaurs to that of whales.

Cymbospondylus youngorum was one of a group of reptiles that returned to the ocean during the Triassic period – the beginning of the age of the dinosaurs – and fully adapted to marine life. Schmitz describes it as a “lizard fish”.

The ichthyosaur fossil found in Nevada – which includes a preserved fin-like skull, shoulder and arm – was discovered in rocks that preserved a cross-section of fauna that existed about five million years later.” the Great Death”. This happened around 252 million years ago, when 81% of the world’s marine life disappeared.

When the skull was discovered, the research team was initially unsure how an animal as large as this could have evolved and survived so soon after the most severe extinction event on Earth.

“The oceans of this period were extremely different from our modern oceans,” Schmitz explained. “The modern marine ecosystems that feed whales today are made up of very large plankton, which did not exist when Cymbospondylus youngorum was around. We found a gigantic ichthyosaur that had lived at a time when the oceans were considered unable to support this size of animal.”

The discovery provided Schmitz and the research team with new insight into how quickly evolution can take place and lead to variety.

“This fossil is an example of how quickly evolution can produce diversity,” Schmitz said. “You can go from zero to 100 in a few million years, which is very fast in terms of evolution.”

The research has been published in the journal Science on Thursday.


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