December 9, 2023

World’s oldest marine reptile found in the Arctic revolutionizes paleontology

For 190 years, researchers have searched for evidence of the origins of marine reptiles from the age of the dinosaurs (the Mesozoic Era), which was suspected to have occurred just after the end of the Permian period. The animals in question were the ichthyosaurs, whose scientific name means “lizard-fish,” which dominated the seas as the first predators 252 million years ago. However, a new discovery has challenged the prevailing theories.

Scientists from Sweden and Norway have been exploring the remote arctic island of Spitsbergen, and have found the oldest ichthyosaur known to mankind. The discovery is described in the scientific journal Current Biology, and involved a great deal of geological development. In the Valley of Flowers, the mountains revealed layers of mudstone that existed at the bottom of the sea 250 million years ago, and with erosion revealed large limestone rocks called concrete, capable of preserving bones in three-dimensional detail.

What we know about ichthyosaurs

Before understanding the amazing nature of the novelty, it is necessary to know what was thought of ichthyosaurs. They were among the first creatures to leave land and adapt to life in the open sea, an evolution similar to that of modern whales. Theories say that after the Permian period, terrestrial reptiles approached the sea to prey on marine prey that had been left without predators due to the mass extinction at the end of the previous geological period.

Over time, the animals became amphibians through natural selection, becoming more efficient at swimming and developing fins instead of legs, until they were shaped like fish and started giving birth to live young without eggs. Without having to go ashore to lay eggs, they’ve severed the last link with the mainland, rising to the top of the marine food chain and dominating the seas.

On a 2014 expedition, scientists collected concrete blocks in Flower Valley and sent them to the Museum of Natural History at the University of Oslo, with support from the Museum of Evolution at Uppsala University. The analysis revealed fossil fish and crocodile-like amphibian bones, as well as 11 articulated vertebrae from the tail of an ichthyosaur. The surprise is that the rocks that preserved the bones are very old for ichthyosaurs, two million years earlier than expected.

A revolution in the evolution of reptiles

Vertebrates are undoubtedly ichthyosaurs, not even ancestors of amphibians, but subject to all the characteristics of animals. Geologically, they are similar to those of large-bodied species, and their preservation has allowed us to study even the delicate internal structures of bones, showing adaptive parameters for rapid growth, high metabolism, and an entirely oceanic lifestyle.

Since the rocks are dated 2 million years before the mass extinction at the end of the Permian period 252 million years ago, the origin and diversification of ichthyosaurs also predates the beginning of the Mesozoic Era. The prevailing view that the age of dinosaurs was a period of emergence for all lineages of reptiles has been challenged, which indicates that some groups appeared before the geological landmark. Scientists are searching for more ancient rocks with ancient secrets, both in Spitsbergen and around the world.

source: Current Biology