Ichthyosaur
An ichthyosaur (Greek for "fish lizard") was a marine reptile that lived during a large part of the Mesozoic era. They appeared slightly earlier than dinosaurs (250 ma versus 230 ma) and disappeared earlier as well (about 90 ma versus 65 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.
Description
Ichthyosaurs averaged 2 to 3 metres in length, with 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.
Althogh 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— 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 fin, which had no hard skeletal structure, until finely-preserved specimens recovered in the 1890s from the Holzmaden lagerstätten in Germany revealed 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 in Tibet. The largest ichthyosaurs exceeded 15 meters.
For their food, many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites. Some early ichthyosaurs had teeth 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, suggesting they have hunted at night.
History of discovery
The first fossil vertebrae were published twice in 1708 as tangible mementos of the Universal Deluge. The first complete ichthyosaur fossil was found in 1811 by Mary Anning in Lyme Regis, along what is now called the Jurassic Coast.
In 1905, the Saurian Expedition led by John C. Merriam of the University of California and financed by Annie Alexander, found 25 specimens in central Nevada, which during the Jurassic was under of a shallow ocean. Several of the specimens are now in the collection of the University of California Museum of Paleontology. Other specimens are embedded in the rock and visible at Berlin-Ichthyosaur State Park in Nye County. An ichthyosaur is the State Fossil of Nevada.
Reference
Stephen Jay Gould, "Bent out of Shape" in Eight Little Piggies.
