Discovery of giant marine reptile skull reveals new evolutionary theories

The giant ichthyosaur fossil – with a skull measuring almost two meters (6.6 feet) long, an estimated body length of over 17 meters (55.7 feet) and a weight of 45 tons – was 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 revealed a new species: Cymbospondylus youngorum.

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

Ichthyosaurs grew to a giant body size in a very short time, evolutionarily, about 3 million years ago. In comparison, whales took about 45 million years to reach their largest size, “Lars Schmitz, associate professor of biology at the WM Keck Science Department – the shared science department of Claremont McKenna, Pitzer and Scripps Colleges in 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 – then conducted a computer analysis comparing the rate and type of change in 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 start of the dinosaur era – and fully adapted to marine life. Schmitz describes him as a “lizard fish”.

The ichthyosaur fossil found in Nevada – which includes a preserved skull, shoulder and arm resembling a fin – was discovered in rocks that preserved a cross section of the fauna that existed around five million years after ” the great death ”. This happened around 252 million years ago, when 81% of the world’s marine life became extinct.

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

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.

“The oceans of this period were vastly 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 incapable of supporting this size of an animal. “

This 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.”

Research has been published in the journal Science Thursday.

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