Fossil clarifies dolphin-like creature’s murky start

(Credit: msr/Flickr)

A newly-discovered fossil is changing ideas about the evolution of the dolphin-like ichthyosaurs, marine reptiles that lived at the same time as land dinosaurs.

The fossil, named Sclerocormus parviceps, turned up in a quarry in Anhui province, China, and appears in a new study in Nature Scientific Reports.

Sclerocormus parviceps
Sclerocormus parviceps. (Credit: Ryosuke Motani)

According to the fossil record, almost all life in the oceans was wiped out in a mass extinction at the end of the Permian period 250 million years ago.

After the catastrophe, reptiles re-colonized the oceans, and eventually ichthyosaurs—air-breathing reptiles with fishlike bodies and large eyes—became an important species. However, their origins have remained murky.

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An analysis of the Sclerocormus fossil allowed researchers to place it among the ancestral ichthyosaurs but separate from any previously known group. The animal was about 5 feet long, and had a short skull, a short, stocky body with four fins, and a long, whiplike tail that took up more than half its body length. The shape of the skull and snout suggest that Sclerocormus fed by sucking in prey, similar to several modern fish.

Because Sclerocormus appears just a few million years (very soon, in geological terms) after the end of the Permian period, and is clearly so different from other fossils of the time, it shows there must have been far more diversity among marine reptiles at the beginning of the Triassic period than had been previously thought, says first author Ryosuke Motani, professor of earth and planetary sciences at the University of California, Davis.

The findings are in line with evidence from fossils of land animals and plants, which show rapid diversification following the mass extinction, researchers say.

Researchers from Peking University, the Anhui Geological Museum, Università degli Studi di Milano, The Field Museum, Chicago, the National Museums Scotland, the Chinese Academy of Sciences; and the Smithsonian Institution are coauthors of the work that was supported by the National Geographic Society and the National Natural Science Foundation of China.

Source: UC Davis