Ichthyosaur is a generic term for an extinct group of aquatic reptiles. There were over 100 distinct types of Ichthyosaur. The most closely resemble porpoises and distant relatives of lizards and snakes (lepidosaurs)
Ichthyosaur fossil remains span almost the entire Mesozoic Era (251 million to 65.5 million years ago). However, they were most common during the Triassic and Jurassic periods (251 million to 145.5 million years ago) about 25 million years before the dinosaurs became extinct. Ichthyosaur fossils have been found on every continent except Africa and Antarctica.
Ichthyosaurus body was streamlined with the head blended smoothly into the body. The limbs were like paddles and used to steer as it propelled itself by using a fishlike tail and by undulating the body. later species had the highest number of fingers: nine to 10 in one hand! The vertebral column was curved downward to the tail. As the bodies of ichthyosaurs thickened over time, the number of vertebrae stayed about the same. To add support to the more voluminous body, the backbone became at least one and a half times thicker than those of the first ichthyosaurs. Because of this thickening, the body became less flexible and the individual vertebrae acquired their hockey-puck appearance.
The skull and jaws of Ichthyosaurus were long and contained numerous sharp teeth. Many of the ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites for their diet. Some early ichthyosaurs had teeth adapted for crushing shellfish. They also most likely fed on fish, and a few of the larger species had heavy jaws and teeth that indicated they fed on smaller reptiles. The eyes were very large that gave these reptiles the ability to see predators (e.g. Pliosaurs) at long distances. Pliosaurs were large marine reptiles that preyed on ichthyosaurs.
Fossils from the western United States and Canada indicate that some ichthyosaurs could exceed 13 metres (43 feet) in length. Deep-bodied and with long fins, these appear to have been ambush predators that fed on fishes. A giant ichthyosaur would have been up to 26 metres near the same size of a blue whale.
Victorian fossil hunting pioneer Mary Anning discovered the first ichthyosaur skeleton on the beach between Charmouth and Lyme Regis when she was just 12 years old.