These days, it’s pretty rare that you hear about something good coming from a melting glacier. But the receding of the Tyndall Glacier in Chile’s Torres del Paine National Park has recently exposed a bounty of 46 ichthyosaurs — an order of predatory marine reptile that patrolled the seas during the Mesozoic era.

Ichthyosaurs were top marine predators that lived from 245 to 90 million years ago. The name “ichthyosaur” is Greek for “fish-lizard,” which is a relatively accurate title. Though these animals breathed air like marine mammals, their spine movement was side-to-side like fish (modern marine mammals move their spines dorsally — up and down — to swim through the water). Despite this difference, ichthyosaurs did have a strikingly similar body plan to dolphins, swimming with pectoral flippers and eating with long, fish-snatching snouts.

The spine of one of the ichthyosaur specimens. The largest ‘fish-lizard’ found was 16′ long and one female specimen had the remains of a developing embryo inside of it. To give you an idea of the size, bottlenose dolphins reach up to 14′ long. 

The abundance of virtually complete ichthyosaur skeletons in one place probably means that all these animals died at the same time, researchers said in the Geological Society of America study. It’s possible that they were all killed by a massive mudslide that started on land and dumped into the sea. When this mudslide occurred, the ichthyosaurs could have become disoriented and drowned. After that, they would have been buried under ocean sediment and preserved. The area where their bodies ended up resting would have been oxygen deficient as well, which is a good precondition for fossil preservation.

Researchers suspect that these ichthyosaurs hunted in an underwater canyon near the coast of Chile. Here, cold water upwellings would have supported an abundance of smaller animals for them to feed on, such as small fish and squid-like animals called belemnites. There is also evidence that these animals could see in very dim light, suggesting that they could have dived deep into the darkness after their prey — much like modern sperm whales.

The particular group of ichthyosaurs found by the Tyndall Glacier are those of the ophthalmosauridae family–a group of ichthyosaurs characterized by bones that formed a sclerotic ring in their eye. This bony ring is thought to have protected and supported the animal’s massive eyes. 

Ichthyosaurs swam during the same eras that the dinosaurs walked the earth, but they were not dinosaurs themselves. Dinosaurs are a specific group of terrestrial animals that are characterized by legs held underneath their bodies, as opposed to having them out to the side like crocodilians (among other features). The exact origins of ichthyosaurs is still debated, but it is is agreed upon that their ancestors had split off from ancient reptiles long before dinosaurs evolved.

Ichthyosaurs would eventually be outlived by another group of reptilian marine predators called plesiosaurs. Recently, work has been done on the bone structures of one group of plesiosaurs called pliosaurs. Little was known about how pliosaurs hunted until recent CT scans of their skulls revealed a vast network of sensory channels leading from the surface of their snout to deep inside their heads. This network of nerves could have helped pliosaurs locate smaller marine life that it could then chomp in half.

In short, marine reptiles get more awesome with each fossil find.

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HT: The Geological Society of America, Scientific American, Natural History Museum, AMNH

IMAGES: OphthalmosaurusIcenius-NaturalHistoryMuseum-August23-08 by Captmondo

VIDEO: BBC’s Walking with Dinosaurs

Ichthyosaur fossil photos published here with permission from Wolfgang Stinnesbeck