For 190 years, researchers have searched for clues to the origin of marine reptiles during the dinosaur era (Mesozoic era), which was suspected to be after the end of the Permian. The animals in question were ichthyosaurs, whose scientific name means “lizard fish,” and dominated the oceans as top predators 252 million years ago. However, a new discovery has challenged prevailing theories.
Scientists from Sweden and Norway have explored the remote Arctic island of Spitsbergen and discovered the oldest ichthyosaur known to mankind. The discovery is described in the journal Science Current Biology, and includes little geographic development. In Malar Valley, the mountains have exposed layers of soil that were at the bottom of the ocean 250 million years ago, and erosion has exposed large limestone boulders called concretions, capable of preserving bones in three-dimensional detail.
What we know about ichthyosaurs
Before understanding the incredible nature of the innovation, it’s important to know what was thought of ichthyosaurs. They were among the first species to leave land and adapt to life in the open ocean, similar to the development of modern whales. After the Permian, the theories suggest that terrestrial reptiles moved closer to the ocean to hunt marine prey left without predators by the mass extinctions at the end of the previous geological period.
Over time, the animals became amphibians through natural selection, becoming more adept at swimming and developing flippers instead of legs, until they were shaped like fish and began to live as young without eggs. Without the need to go ashore to lay their eggs, severing their last link to land, they rise to the top of the marine food chain and dominate the oceans.
On a 2014 expedition, scientists collected concretions in the Flower Valley and sent them to the Natural History Museum at the University of Oslo with the support of the Museum of Evolution at Uppsala University. Analysis revealed bony fish fossils and crocodile-like amphibian bones and 11 articulated vertebrae from the tail of an ichthyosaur. Surprisingly, the rocks that preserve the bones are much older than expected for ichthyosaurs, about 2 million years earlier.
A revolution in reptile evolution
Vertebrates are undoubtedly descended from ichthyosaurs, not even from the amphibious ancestor of animals, but obey all the characteristics of animals. Geographically, they resemble large-bodied creatures, and their preservation has even allowed us to study the internal microstructures of their bones, showing the adaptive milestones of rapid growth, high metabolism, and a completely marine lifestyle.
The appearance and diversification of ichthyosaurs also predates the start of the Mesozoic, with rocks dating to 252 million years ago, 2 million years before the Permian mass extinction. The popular view that the age of the dinosaurs was the time when all reptiles descended has been challenged, showing that some groups appeared before the geological milestone. Scientists are searching for the oldest rocks in Spitsbergen and around the world that hold ancient secrets.
Source: Current Biology
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