Earliest known ichthyosaur fossil discovered in Arctic island of spitsbergen

For almost two centuries, scientists have been seeking the origins of ancient sea-faring reptiles from the Age of Dinosaurs. Recently, a group of paleontologists from Sweden and Norway have made a breakthrough discovery on the remote Arctic island of Spitsbergen. They have found remains of the earliest known ichthyosaur, also known as “fish-lizard”, which has been documented in a paper published in Current Biology.

Ichthyosaurs are a group of marine reptiles that have been extinct for a long time, and their fossils have been found across the world. They were one of the first land animals to adapt to life in the open sea and developed a body shape similar to modern whales. While dinosaurs roamed the land, ichthyosaurs were at the top of the food chain in the oceans, dominating marine habitats for over 160 million years.

According to textbooks, after the end-Permian mass extinction, which had a catastrophic impact on marine ecosystems and marked the beginning of the Age of Dinosaurs almost 252 million years ago, reptiles first ventured into the open sea. The story goes that land-based reptiles with legs for walking moved into shallow coastal environments to exploit marine predator niches that were left unoccupied by this catastrophic event. These early amphibious reptiles gradually became better swimmers and modified their limbs into flippers, developed a fish-like body shape, and ultimately evolved to give birth to live young, thus severing their final link with the land by no longer needing to come ashore to lay eggs.

Computed tomography image and cross-section showing internal bone structure of vertebrae from the earliest ichthyosaur. Credit: Øyvind Hammer and Jørn Hurum

The long-held theory about the evolution of ancient sea-faring reptiles has been challenged by new fossils discovered on Spitsbergen. The fossils were found in Flower’s valley, located near the hunting cabins on the southern shore of Ice Fjord in western Spitsbergen. The valley exposes rock layers that were once mud at the bottom of the sea around 250 million years ago, and the mudstone has been eroded away by a fast-flowing river, revealing limestone boulders called concretions. These concretions have preserved the remains of ancient sea creatures in exceptional three-dimensional detail.

In 2014, a large number of concretions were collected from Flower’s valley and taken to the Natural History Museum at the University of Oslo for future study. Researchers from the Museum of Evolution at Uppsala University have now analyzed the concretions and found bony fish and crocodile-like amphibian bones, as well as 11 articulated tail vertebrae from an ichthyosaur.

What’s surprising is that the ichthyosaur vertebrae were found in rocks that were supposedly too old for ichthyosaurs. Additionally, the vertebrae are identical to those of larger-bodied ichthyosaurs from a much later period, rather than resembling the textbook example of an amphibious ichthyosaur ancestor. The internal bone microstructure of the vertebrae also shows characteristics of fast growth, elevated metabolism, and a fully oceanic lifestyle.

Fossil-bearing rocks on Spitsbergen that produce the earliest ichthyosaur remains. Credit: Benjamin Kear

The age of the newly discovered fossils was confirmed through geochemical testing of the surrounding rock, revealing that they existed approximately two million years after the end-Permian mass extinction. This finding challenges the current understanding of oceanic reptile evolution and pushes back the origin and early diversification of ichthyosaurs to a time before the Age of Dinosaurs began. As a result, the textbook interpretation of ichthyosaur evolution needs to be revised, as it seems these creatures first adapted to marine environments prior to the extinction event.

This groundbreaking discovery also suggests that other major reptile lineages may have emerged before the Age of Dinosaurs, as some groups likely predated this landmark interval. It’s possible that even older rocks on Spitsbergen and other parts of the world may contain fossils of their most ancient ancestors, waiting to be discovered by paleontologists.

Source: Uppsala University

Leave a Comment