Ichthyosaurs (meaning fish and lizard) were huge marine reptiles that resembled fish and dolphins.

Ichthyosaurs lived during a big part of the Mesozoic era, having appeared about 230 million years back, faintly when the dinosaurs appeared (230 million years past); and disappeared about 90 million years before about 25 million years earlier than the dinosaurs becameextinct.

During the hub Triassic Period, ichthyosaurs evolved from nameless land reptiles that moved back into the water, in a development parallel to that of contemporary dolphins and whales. They were particularly plentiful in the Jurassic Period, until they were replaced as the top marine predators by plesiosaurs in the Cretaceous Period.

Ichthyosaurs were strong swimmers completely adapted to life in the seas. They were improved adapted than any other reptiles, although they still needed to go to the surface sporadically to breathe air.

They belong to the order known as Ichthyosauria or Ichthyopterygia. Ichthyosaurs averaged 2 to 4 metres in span, with a porpoise-like head and a long, toothed nose. Built for speed, like contemporary tuna, some ichthyosaurs emerge also to have been deep divers. It has been anticipated that ichthyosaurs could swim at speed up to 40 km/h (25 mph).

Alike to modern cetaceans such as whales and dolphins, they were air-breathing and also were viviparous (embryo develops inside the body of the mother, from which it gains sustenance, as opposed to in an egg). Although they were reptiles and descended from egg-laying intimates, viviparity is not as unforeseen as it first appears. All air-breathing marine creatures must either come aground to lay eggs, like turtles and some sea snakes, or else give birth to live immature in surface waters, like whales and dolphins.

Given their streamlined bodies, heavily tailored for fast swimming, it would have been tricky for ichthyosaurs to scramble successfully onto land to lay eggs.

They considered around 2.4 metres (8 feet) and weighed around 163 to 168 kg (360 to 370 lb).

Though ichthyosaurs looked like fish, they were not. Ichthyosaurs had fin-like limbs, which were probably used for stabilisation and directional organize, rather than propulsion, which would have come from the large shark-like tail. The tail was bi-lobed, with the inferior lobe being supported by the caudal vertebral column, which was kinked ventrally to follow the contours of the ventral lobe.


Ichthyosaurs were carnivores and they ate fish, octopus and other swimming animals with their burly jaws and jagged teeth. They also relied heavily on very old cephalopod called belemnites. However, Ichthyosaurs ranged so lengthily in size, and survived for so long, that they are likely to have had a wide variety of prey. Typical ichthyosaurs have very big eyes, protected within a bony ring, suggesting that they may have hunted at night.

Ichthyosaurs were still general in the Middle Jurassic, but had now decreased in diversity. All belonged to the sole clade Ophthalmosauria.

Ichthyosaurs seemed to reduce in diversity even further with the Cretaceous. Only a single genus is known, Platypterygius, and although it had a universal distribution, there was small diversity species-wise. This last ichthyosaur genus fell victim to the mid-Cretaceous (Cenomanian-Turonian) extinction event (as did some of the giant pliosaurs), although paradoxically less hydrodynamically well-organized animals like mosasaurs and long-necked plesiosaurs flourished.

Ichthyosaur fossils have been established in North and South America and Europe.

Scientific Classification:

Kingdom: Animalia

Phylum: Chordata

Class: Sauropsida

Subclass: Diapsida?

Superorder: Ichthyopterygia

Order: Ichthyosauria