Restoration of the earliest ichthyosaur and the 250-million-year-old community found on Spitsbergen. Credit: Illustration by Esther van Hulsen
For almost 190 years, scientists have looked for the origins of ancient sea-going reptiles from the Age of Dinosaurs. Now a group of Norwegian and swedish palaeontologists has actually found remains of the earliest recognized ichthyosaur or fish-lizard on the remote Arctic island of Spitsbergen.
Ichthyosaurs were an extinct group of marine reptiles whose fossils have been recovered worldwide. They were among the first land living animals to adjust to life outdoors sea, and evolved a fish-like body shape comparable to contemporary whales. Ichthyosaurs were at the top of the food cycle in the oceans while dinosaurs wandered the land, and dominated marine environments for over 160 million years.
Calculated tomography image and cross-section revealing internal bone structure of vertebrae from the earliest ichthyosaur. Credit: Øyvind Hammer and Jørn Hurum
According to the textbooks, reptiles first ventured into the ocean blue after the end-Permian mass termination, which devastated marine communities and led the way for the dawn of the Age of Dinosaurs almost 252 million years ago. As the story goes, land-based reptiles with walking legs invaded shallow seaside environments to take benefit marine predator niches that were left uninhabited by this cataclysmic event. In time, these early amphibious reptiles became more effective at swimming and ultimately modified their limbs into flippers, established a fish-like body shape, and began bring to life live young; thus, severing their final tie with the land by not needing to come ashore to lay eggs.
The brand-new fossils discovered on Spitsbergen are now modifying this long accepted theory.
Close to the hunting cabins on the southern coast of Ice Fjord in western Spitsbergen, Flowers valley cuts through snow-capped mountains exposing rock layers that were once mud at the bottom of the sea around 250 million years ago. A fast-flowing river fed by snow melt has actually worn down away the mudstone to expose rounded limestone boulders called concretions. These formed from limey sediments that settled around decomposing animal stays on the ancient seabed, subsequently maintaining them in incredible three-dimensional information. Paleontologists today hunt for these concretions to analyze the fossil traces of long-dead sea creatures.
Fossil-bearing rocks on Spitsbergen that produce the earliest ichthyosaur stays. Credit: Benjamin Kear
Throughout an expedition in 2014, a large number of concretions were gathered from Flowers valley and delivered back to the Natural History Museum at the University of Oslo for future study. Research study performed with The Museum of Evolution at Uppsala University has now identified bony fish and strange crocodile-like amphibian bones, together with 11 articulated tail vertebrae from an ichthyosaur. All of a sudden, these vertebrae happened within rocks that were supposedly too old for ichthyosaurs. Likewise, instead of representing the book example of an amphibious ichthyosaur forefather, the vertebrae are similar to those of geologically much younger larger-bodied ichthyosaurs, and even preserve internal bone microstructure revealing adaptive hallmarks of fast development, raised metabolic process and a fully oceanic way of life.
Geochemical screening of the surrounding rock validated the age of the fossils at approximately two million years after the end-Permian mass extinction. Given the approximated timescale of oceanic reptile development, this presses back the origin and early diversification of ichthyosaurs to before the beginning of the Age of Dinosaurs; thereby forcing a modification of the textbook interpretation and revealing that ichthyosaurs most likely first radiated into marine environments prior to the termination occasion.
Excitingly, the discovery of the earliest ichthyosaur rewrites the popular vision of Age of Dinosaurs as the emergence timeframe of major reptile family trees. It now seems that a minimum of some groups predated this landmark period, with fossils of their most ancient ancestors still awaiting discovery in even older rocks on Spitsbergen and somewhere else in the world.
The paper is published in the prestigious global life sciences journal Current Biology.
Referral: “Earliest Triassic ichthyosaur fossils push back oceanic reptile origins” by Benjamin P. Kear, Victoria S. Engelschiøn, Øyvind Hammer, Aubrey J. Roberts and Jørn H. Hurum, 13 March 2023, Current Biology.DOI: 10.1016/ j.cub.2022.12.053.
According to the books, reptiles initially ventured into the open sea after the end-Permian mass extinction, which ravaged marine environments and paved the way for the dawn of the Age of Dinosaurs nearly 252 million years earlier. Close to the hunting cabins on the southern shore of Ice Fjord in western Spitsbergen, Flowers valley cuts through snow-capped mountains exposing rock layers that were as soon as mud at the bottom of the sea around 250 million years back. Research performed with The Museum of Evolution at Uppsala University has actually now recognized bony fish and unusual crocodile-like amphibian bones, together with 11 articulated tail vertebrae from an ichthyosaur. Suddenly, these vertebrae took place within rocks that were supposedly too old for ichthyosaurs. Rather than representing the textbook example of an amphibious ichthyosaur forefather, the vertebrae are identical to those of geologically much younger larger-bodied ichthyosaurs, and even protect internal bone microstructure revealing adaptive trademarks of quick growth, elevated metabolism and a totally oceanic way of life.