Ichthyosaurs

 

Ichthyosaur is Greek for ‘fish lizard’, and is the name for a group of large extinct marine reptiles. They lived during the time of the dinosaurs, but formed a separate group from them and may not have been closely related.

Ichthyosaurs thrived during much of the Mesozoic era. Based on fossil evidence, they appeared about 250 million years ago, and at least one species survived until about 90 million years ago, during the Late Cretaceous. During the early Triassic period, ichthyosaurs evolved from some unidentified land reptile that returned to the sea. In a case of convergent evolution, they gradually came to resemble modern dolphins and whales, which evolved from land-dwelling mammals millions of years after the ichthyosaurs returned to the ocean. These ‘fish lizards’ were abundant until the later Jurassic and Cretaceous periods, when they were replaced as the top aquatic predators by the Plesiosauria, another marine reptilian group.

Ichthyosaurs averaged 2-4 meters (6.6 to 13.1 ft) in length. Some specimens were as short as 1 ft, while other species were much larger. During the Triassic, the Shonisaurus popularis was about 15 meters (49 ft) long. The Shastasaurus sikanniensis was estimated in 2004 to have been 21 meters (69 ft) long. Some lower jaw fragments found in England indicated a length between 20 and 25 meters (66 to 82 ft).

Weight estimates indicate a 2.4 meter (8 ft) Stenopterygius weighed around 163-168 kg (359-370 lb), while a 4 meter (13 ft) Ophthalmosaurus icenicus weighed 930-950 kg (2,050-2,090 lb). That would be a lot of tuna! Or salmon.

The earliest members of the ichthyosaur lineage were eel-like, but later members resembled more typical fishes or dolphins. Their limbs had been fully transformed into flippers, and some species had a fin on their backs and a more vertical fin at the rear of a rather short tail.

Their heads were pointed, and the jaws often came equipped with conical teeth to catch smaller prey. Some species had larger, bladed teeth to attack large animals. Their eyes were very large and the neck was short. Later species had a stiff trunk with a more vertical tail fin, which made for a powerful propulsive stroke. Ichthyosaurs were air-breathing, warm-blooded and bore live young. It’s possible they had a layer of blubber for insulation.

They may have looked like fish, but they were not. They were reptiles. They adapted so well to their environment that some of them developed dorsal fins and vertical tail fins without their ancestors having had anything there to be adapted.

 

https://en.wikipedia.org/wiki/Ichthyosaur