Researchers have uncovered a Lower Cretaceous graveyard containing the fossils of nearly 50 ichthyosaurs by a glacier in southern Chile. Named for “fish lizards,” these marine reptiles resembled giant fish or even dolphins, and likely fed on squid-ancestors and fish near the coastline.
After three arduous trips to the vicinity of Tyndall Glacier in the Torres del Paine National Park of Chile, an international team led by Wolfgang Stinnesbeck of Ruprecht-Karls-Universität Heidelberg found a total of 46 articulated and virtually complete ichthyosaur specimens in an Early Cretaceous deposit (about 150 million to 100 million years ago). These extremely well preserved remains include both adults and juveniles, as well as soft tissue and even embryos inside a specimen.
The team temporarily assigned the newly discovered skeletons to four different species in the extinct family Ophthalmosauridae.
The abundance of these almost completely articulated ichthyosaur skeletons in the glacier area suggests that they fell victim to a series of mass-mortality events caused by thick, sediment-filled currents traveling downslope through a submarine canyon. The ancient reptiles likely lost orientation, drowned, and were then dragged into the deep sea by turbulent mudflows. Their bodies ended up in an oxygen-deficient basin, where they were immediately embedded by the cascade of fine sediment.
The rock containing the fossils were later exposed by the melting glacier. Very few ichthyosaurs have been found in South America: a few rib cage bits and vertebrae have been previously unearthed. These new skeletons were found along with ammonites, extinct cephalopods called belemnites, oyster-like inoceramid bivalves, and fishes, as well as plants.
Ichthyosaurs may have died out before the dinosaurs on land and pterosaurs in the air. As Stinnesbeck explains to LiveScience, global depletion of oxygen in the oceans -- possibly due to volcanism -- may have caused the extinction of these seagoing reptiles.
The work was published in the Geological Society of America (GSA) Bulletin last week.
Image: Nobu Tamura via Wikimedia