Ichthyosaurus: Jurassic Marine Reptile

Ichthyosaurus was a dolphin-like marine reptile that lived during the early Jurassic through the early Cretaceous Period. It belonged to a family of marine reptiles called ichthyosaurs, but was rather small for a typical member of this family (large ichthyosaurs could reach lengths of 30 feet). Ichthyosaurus was one of the first fossilized marine reptiles to be uncovered and hundreds of fossilized remains have been uncovered in England, Germany, Greenland, and Alberta.

This small marine reptile was only about six feet long, with a dolphin or porpoise-like body and a large, boomerang-shaped tail. It had a long snout which was lined with sharp teeth for catching slippery fish, a long dorsal fin, and giant eyes. Because of their muscular, streamlined body and large fins, ichthyosaurus could probably move very quickly though the water, perhaps up to 25 miles per hour. This would have been a strong advantage for catching smaller, fast-moving prey like fish, squid, and octopi. The ichthyosaurus' gigantic, saucer-sized eyes would have allowed it to see well in the ocean gloom, either in the shallows or in dark water. These eyes are actually among the largest on Earth, dwarfed only by a giant squid's and likely contained a large number of specialized light-sensitive receptors. In addition, ichthyosaurus had a developed sense of hearing which could have allowed it to sense vibrations made by prey in the water.

Unlike most reptiles, ichthyosaurus did not lay eggs, but rather gave birth to live young. Evidence for this live-birth is seen in the fossil record of ichthyosaurus in which the bones of young have been found inside the body cavity. Giving birth to young underwater means it would have needed to deliver the baby tail-first so that it could still breathe before having the opportunity to surface. Unlike fish which have gills, reptiles and mammals living in the water have to surface for air, and ichthyosaurus is no exception. The nostrils of ichthyosaurus were located near the eyes at the top of the head which would have made respiration easier. Instead of having to swim upright to breathe through the mouth, ichthyosaurus could swim horizontally up to the surface and retain speed.

Ichthyosaurs died out around 95 million years ago, nearly 30 million years before the famed Cretaceous-Tertiary extinction event. After being successful ocean predators for much of the Mesozoic, they set the stage for the demise of all other marine reptile predators.