Ichthyosaur

A newer version of this article is available: see Ichthyosaur at Schools Wikipedia

An ichthyosaur (Greek for "fish lizard") was a marine reptile that lived during a large part of the Mesozoic period. They appeared slightly earlier than dinosaurs (250 million years ago versus 230 ma) and disappeared earlier, too, about 90 ma. During the early Triassic, Ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water (analogous in that way to dolphins and whales). They were particularly abundant in the Jurassic period. They belong to the order Ichthyosauria.

Ichthyosaurs averaged 2 to 3 metres in length. They had a porpoise-like head and a long, toothed snout. They had a large tail fin and their limbs were adapted for use as steering paddles. They were carnivorous, coming to the surface to fill their lungs with air and viviparous, for fossils have been found with their fossilized fetal young. Built for speed, like modern tuna, they also apparently were deep divers, like some modern whales.

Though they looked like fish they were not. Biologist Stephen Jay Gould said the ichthyosaur was his favorite example of convergent evolution, where similarities of structure are analogous not homologous, for this group

"converged so strongly on fishes that it actually evolved a dorsal fin and tail in just the right place and with just the right hydrological design. These structures are all the more remarkable because they evolved from nothing&mdash the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor."

In fact the earliest reconstructions of ichthyosaurs omitted the dorsal lin, which had no hard skeletal structure, until finely-preserved specimensrecovered in the 1890s from the Holzmaden lagerstätten in Germany revealed the traces of the fin. The earliest ichthyosaurs, looking more like finned lizards than the familiar fish or dolphin forms, are known from the Lower Triassic strata of Canada, China, Japan, and Spitsbergen in Norway. Late Jurassic Himalayasaurus tibetensis was found, as you may have suspected, in Tibet. The largest Ichthyosaurs exceeded 15 meters.

Many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites for their food.Some early Ichthyosaurs had yeeth adapted for crushing shellfish. Ichthyosaurs ranged so widely in size, and survived so long, they are likely to have had a wide range of prey.

Typical ichthyosaurs have very large eyes, protected within a bony ring. Did they hunt at night?

Though fossil vertebrae had been published (twice) in 1708, incidentally providing tangible mementos of the Univrersal Deluge, the first Icomplete chthyosaur fossil was found by Mary Anning in Lyme Regis, along what is now called the Jurassic Coast, in 1811. An ichthyosaur is the State Fossil of Nevada, which was a shallow Jurassic inland ocean.

Reference

Stephen Jay Gould, "Bent out of Shape" in Eight Little Piggies.

Ichthyosaur

Reference

External links