Scientists have been investigating the origin of ancient marine reptiles in the age of the dinosaurs for almost 190 years. Now a team of Swedish and Norwegian paleontologists has discovered the remains of the oldest ichthyosaur, or “fish lizard,” on the remote Arctic island of Svalbard. Ichthyosaurs were an extinct group of marine reptiles whose fossils have been found all over the world. They were among the first land animals to adapt to life in the open sea and developed a “fish-like” body shape similar to modern whales. While ichthyosaurs were at the top of the oceanic food chain, dinosaurs roamed land and dominated marine environments for over 160 million years.
According to textbooks, reptiles entered the open sea for the first time after the mass extinction at the end of the Permian period, about 252 million years ago, that devastated marine ecosystems and set the stage for the start of the age of dinosaurs. According to the story, walking-footed terrestrial reptiles invaded shallow coastal environments to take advantage of the marine predator niches left empty by this catastrophic event. Eventually, these early amphibian reptiles became more adept at swimming and eventually turned their limbs into fins, developed a “fish” body shape and began giving birth at a young age; so they do not have to come ashore to lay their eggs, thus severing their final contact with land.
New fossils discovered at Svalbard now revise this long-held theory.
Located near the hunting lodges on the south bank of the Icefjord west of Svalbard, the Kvitka Valley cuts through snow-topped mountains, revealing layers of rock that were once silt on the seafloor 250 million years ago. A fast-flowing river fed by melting snow eroded the mudstone to reveal rounded blocks of limestone called nodules. They formed from calcareous sediments that settled around decomposed animal remains on the ancient seafloor, and later preserved them in impressive three-dimensional detail. Today, paleontologists seek out these concretes to study fossilized traces of long-dead sea creatures.
Much concrete was collected from the Kvitka Valley during the 2014 expedition and sent back to the Natural History Museum at the University of Oslo for further study. The research, conducted in collaboration with Uppsala University’s Museum of Evolution, revealed 11 articulated ichthyosaur tail vertebrae, as well as bony fish and strange “crocodile” amphibian bones. Unexpectedly, these vertebrae were found in rocks that were probably too old for ichthyosaurs. Also, instead of representing the textbook example of an amphibious ichthyosaur ancestor, the vertebrae are geologically much the same as those of much younger, larger-bodied ichthyosaurs, and even retain the internal microstructure of bone, showing adaptive signs of rapid growth, increased metabolism, and a purely oceanic lifestyle.
Geochemical studies of the surrounding rock confirmed the age of the fossils, about two million years after the mass extinction at the end of the Permian period. Given the approximate timescale of the evolution of oceanic reptiles, this traces the origin and early diversification of ichthyosaurs back to the beginning of the age of dinosaurs; thus necessitating a revision of textbook interpretation, and found that ichthyosaurs probably first spread into the marine environment before the extinction event.
Interestingly, the discovery of the oldest ichthyosaur rewrites the popular view of the age of dinosaurs as the period when the main reptiles emerged. It now appears that at least some groups arose before this pivotal period, with fossils of their oldest ancestors waiting to be discovered in older rocks at Svalbard and elsewhere in the world.
Source: Port Altele
