Ichthyosaurs (Greek for "fish lizards") were giant marine reptiles that resemble a dolphin with teeth (see convergent evolution). They lived during a large part of the Mesozoic era, and appeared about 250 million years ago (Ma), slightly earlier than the dinosaurs (230 Ma); and disappeared about 90 Ma, about 25 million years before the dinosaurs became extinct. During the early Triassic, ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water, in a development similar to dolphins' and whales'. They were particularly abundant in the Jurassic period, until they were replaced as the top aquatic predators by plesiosaurs in the Cretaceous. They belong to the order known as Ichthyosauria or Ichthyopterygia ("fish flippers" a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria). Euryapsids Plesiosaurs Ichthyosaurs placodonts Diapsids mosasaurs marine crocodiles marine Iguanas Categories: Lists of animals | Reptiles ... In evolutionary biology, convergent evolution describes the process whereby organisms not closely related independently acquire similar characteristics while evolving in separate and sometimes varying ecosystems. ... The Mesozoic is one of three geologic eras of Phanerozoic eon. ... Mega-annum, usually abbreviated as Ma, is a unit of time equal to one million years. ... Orders Saurischia    Sauropodomorpha    Theropoda Ornithischia Dinosaurs are animals that dominated the terrestrial ecosystem for over 100 million years. ... The Triassic is a geologic period that extends from about 245 to 202 million years ago (mya). ... Genera See article below. ... Whales are the largest species of exclusively aquatic placental mammals, members of the order Cetacea, which also includes dolphins and porpoises. ... The Jurassic period is a major unit of the geologic timescale that extends from about 200 million years BP at the end of the Triassic to 146 million years BP at the beginning of the Cretaceous. ... Families Cryptoclididae Elasmosauridae Plesiosauridae Pliosauridae Plesiosaurs (PLEE-see-oh-SORES) were large, carnivorous aquatic reptiles. ... The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period (about 135 mya) to the beginning of the Paleocene epoch of the Tertiary period (65 mya). ... Sir Richard Owen and Dinornis bird skeleton Sir Richard Owen (July 20, 1804 - December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ...

Description

Ichthyosaurs averaged 2 to 4 metres in length (although a few were smaller, and some species grew much larger), 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. Viviparity should not be as surprising as it appears at first: air-breathing marine creatures must come ashore to lay eggs, like turtles and some sea snakes, or else give birth to live young in surface waters. Built for speed, like modern tuna, ichthyosaurs also apparently were deep divers, like some modern whales (Motani, 2000). It has been estimated that ichthyosaurs could swim at speeds up to 25 mph (40 km/h). Genera Neophocaena Phocoena - Harbor porpoises Phocoenoides - Dalls porpoises The porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. ... This article deals with meat-eating animals. ... A viviparous animal is an animal employing vivipary, a method of reproduction in which the embryo develops inside the body of the mother from which it gains nourishment, and not from an egg. ... Species Thunnus alalunga Thunnus albacares Thunnus atlanticus Thunnus maccoyii Thunnus obesus Thunnus orientalis Thunnus thynnus Thunnus tonggol Tuna are several species of ocean-dwelling fish in the family Scombridae, mostly in the genus Thunnus. ...

According to weight estimates by Ryosuke Motani [1] a 2.4 meter (8 ft) Stenopterygius weighed around 163 to 168 kg (360 to 370 lb), whilst a 4.0 meter (13 ft) Ophthalmosaurus icenicus weighed 930 to 950 kg (about a ton).

Although ichthyosaurs 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: Stephen Jay Gould Stephen Jay Gould (September 10, 1941 – May 20, 2002) was a New York-born American paleontologist, evolutionary biologist, and historian of science. ... In evolutionary biology, convergent evolution describes the process whereby organisms not closely related independently acquire similar characteristics while evolving in separate and sometimes varying ecosystems. ... An analogy is a comparison between two different things, in order to highlight some form of similarity. ... Two or more structures are said to be homologous if they are alike because of shared ancestry. ...

"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."

Drawing of an Ichthyosaur skeleton

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. Dorsal Fin of the Orca A dorsal fin is a fin located on the backs of fishes, whales, dolphins and porpoises. ... Drawing of an Ichthyosaur skeleton, scanned from a copyright free source. ... Drawing of an Ichthyosaur skeleton, scanned from a copyright free source. ... The 1890s were sometimes referred to as the Mauve Decade, because William Henry Perkins aniline dye allowed the widespread use of that color in fashion, and also as the Gay Nineties, under the then-current usage of the word gay which referred simply to merriment and frivolity, with no... Holzmaden is a town in Germany near Württemberg containing rich layers of well preserved fossils (or Lagerstätten) of the Jurassic period. ... Lagerstätten (German, singular: Lagerstätte, literally: place(s) of storage or resting place(s)) are sedimentary deposits that exhibit extraordinary fossil richness or completeness. ...

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. 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. Ichthyosaurs ranged so widely in size, and survived for so long, that they are likely to have had a wide range of prey. Typical ichthyosaurs have very large eyes, protected within a bony ring, suggesting they may have hunted at night. Orders Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida Nautilida The Cephalopods (head-foot) are the mollusc class Cephalopoda characterized by bilateral body symmetry, a prominent head, and a modification of the mollusc foot into the form of arms or tentacles. ... Suborders Myopsina Oegopsina Squids are the large, diverse group of marine mollusks, popular as food in cuisines as widely separated as the Korean and the Italian. ... Extinct Orders Aulacocerida Phragmoteuthida Belemnitida Diplobelida Belemnoteuthina Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the modern cuttlefish. ... Shellfish is a term used to describe molluscs and crustaceans used as food. ...

History of discoveries

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. Tentaculites found in a State Park in Albany, New York, believed to have existed over 360 million years ago. ... A diagram of a thoracic vertebra. ... // Events March 23 - James Francis Edward Stuart lands at the Firth of Forth July 1 - Tewoflos becomes Emperor of Ethiopia September 28 - Peter the Great defeats the Swedes at the Battle of Lesnaya Kandahar conquered by Mir Wais In Masuria one third of the population die during the plague J... The Deluge by Gustave Doré The story of a Great Flood sent by God or gods to destroy civilization is a widespread but not universal theme in myth. ... 1811 was a common year starting on Tuesday (see link for calendar). ... Mary Anning (May 21, 1799 - March 9, 1847) was an early British fossil collector and paleontologist. ... Categories: Stub | Towns in Dorset | English seaside resorts ... Lulworth Cove The Jurassic Coast is a World Heritage Site in south England. ...

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 Triassic was under 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. In 1977 the Triassic ichthyosaur Shonisaurus is the State Fossil of Nevada. Nevada is the only state to possess a complete skeleton, 55 ft (17 m) of this extinct marine reptile. 1905 was a common year starting on Sunday (see link for calendar). ... The Saurian Expedition of 1905 was a noted paleontological research mission in northern Nevada in the United States. ... John Campbell Merriam (October 20, 1869 - October 30, 1945) was an American paleontologist. ... The University of California (UC) is a public university system within the State of California. ... Annie Montague Alexander (1867-1950) was an American financier and paleontological collector. ... State nickname: Silver State, Battle Born State (official) Other U.S. States Capital Carson City Largest city Las Vegas Governor Kenny Guinn (R) Official languages None Area 286,367 km² (7th)  - Land 284,396 km²  - Water 1,971 km² (0. ... The University of California (UC) is a public university system within the State of California. ... The Berlin-Ichthyosaur State Park is a state park of the U.S. state of Nevada. ... Nye County is a county located in the state of Nevada. ... 1977 was a common year starting on Saturday (the link is to a full 1977 calendar). ... Though every state in the United States has a State Bird and a State Flower, not every state in the United States has a State Fossil. ...

Evolutionary history

The earliest ichthyosaurs, looking more like finned lizards than the familiar fish or dolphin forms, are known from the Early and Early-Middle (Olenekian and Anisian) Triassic strata of Canada, China, Japan, and Spitsbergen in Norway. These primitive forms included the genera Chaohusaurus, Grippia, and Utatsusaurus. These very early proto-ichthyosaurs, which are now classified as Ichthyopterygia rather than as ichthyosaurs proper (Motani 1997, Motani et al. 1998), quickly gave rise to true ichthyosaurs sometime in the latest Early Triassic or earliest Middle Triassic. These latter diversified into a variety of forms, including the sea-serpant like Cymbiospondylus, which reached 10 meters, and smaller more typical forms like Mixosaurus. By the Late Triassic, ichthyosaurs consisted of both classic Shastasauria and more advanced, "dolphin"-like Euichthyosauria (Californosaurus, Toretocnemus) and Parvipelvia (Hudsonelpidia, Macgowania). Experts disagree over whether these represent an evolutionary continum, with the less specialised shastosaurs a paraphyletic grade that was evolving into the more advanced forms (Maisch and Matzke 2000), or whether the two were separate clades that evolved from a common ancestor earlier on (Nicholls and Manabe 2001). The Triassic is a geologic period that extends from about 245 to 202 million years ago (mya). ... Spitsbergen is the largest island in the Svalbard archipelago, which is situated in the Arctic Ocean and administered by Norway. ... Groups Utatsusaurus Parvinatator Eoichthyosauria Grippidae/Grippidia Ichthyosauria Ichthyopterygia (fish flippers) was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic Ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle... Paraphyletic - Wikipedia /**/ @import /skins-1. ... Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ...

During the Carnian and Norian, shastosaurs reached huge sizes. Shonisaurus popularis, known from a number of specimens from the Carnian of Nevada, was 15 meters long. Norian shonisaurs are known from both sides of the Pacific. Himalayasaurus tibetensis and Tibetosaurus (probably a synonym) have been found in Tibet. These large (10 to 15 meters long) ichthyosaurs probably belong to the same genus as Shonisaurus (Motani et al, 1999; Lucas, 2001, pp.117-119). While the gigantic Shonisaurus sikanniensis, whose remains were found in the Pardonet formation of British Columbia by Elizabeth Nicholls, reached as much as 23 meters in length - the largest marine reptile known to date. Tibet (Tibetan: བོད་, Bod, pronounced pö in Lhasa dialect; Chinese: 西藏, pinyin: Xīzàng) is a region and former independent country in Central Asia and the home of the Tibetan people. ...

These giants (along with their smaller cousins) seemed to have disappeared at the end of the Norian. Rhaetian (latest Triassic) ichthyosaurs are known from England, and these are very similar to those of the Early Jurassic. Like the dinosaurs, the ichthyosaurs and their contemporaries the plesiosaurs survived the end-Triassic extinction event, and immediately diversified to fill the vacant ecological niches of the earliest Jurassic. Lower Jurassic (also known as Lias) is the earliest of three epochs of Jurassic period. ...

The Early Jurassic, like the Late Triassic, was the heyday of the ichthyosaurs, which are represented by four families and a variety of species, ranging from one to ten meters in length. Genera include Eurhinosaurus, Ichthyosaurus, Leptonectes, Stenopterygius, and the large predator Temnodontosaurus, along with the persistantly primitive Suevoleviathan, which was little changed from its Norian ancestors. All these animals were streamlined, dolphin-like forms, although the more primitive animals were perhaps more elongated than the advanced and compact Stenopterygius and Ichthyosaurus.

Ichthyosaurs were still common in the Middle Jurassic, but had now decreased in diversity. All belonged to the single clade Ophthalmosauria. Represented by the 4 meter long Ophthalmosaurus and related genera, they were very similar to Ichthyosaurus, and had attained a perfect "tear-drop" streamlined form. The eyes of Ophthalmosaurus were huge, and it is likely that these animals hunted in dim and deep water (Motani 2000). The Middle Jurassic, called the Dogger in the European system of classification, is the second epoch of the Jurassic period. ...

Ichthyosaurs seemed to decrease in diversity even further with the Cretaceous. Only a single genus is known, Platypterygius, and although it had a worldwide distribution, there was little 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 ironically less hydrodynomically efficient animals like Mosasaurs and long-necked Plesiosaurs flourished. It seems that the ichthyosaurs became the victim of their own overspecialisation, and were unable to keep up with the fast swimming and highly evasive new teleost fishes that were becoming dominant at this time, and against which the sit and wait ambush strategies of the mosasaurs proved superior (Lingham-Soliar 1999). The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period (about 135 mya) to the beginning of the Paleocene epoch of the Tertiary period (65 mya). ... Subfamilies Mosasaurinae Plioplatecarpinae Tylosaurinae A mosasaur was not a dinosaur, but rather an ocean-dwelling serpentine marine reptile more closely related to snakes than to monitor lizards (Lee 1997). ... Orders See text The Actinopterygii are the ray-finned fish. ...

References

• Ellis, Richard, (2003) Sea Dragons - Predators of the Prehistoric Oceans. University Press of Kansas ISBN 0-7006-1269-6

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

• Lingham-Soliar, T. (1999): A functional analysis of the skull of Goronyosaurus nigeriensis (Squamata: Mosasauridae) and Its Bearing on the Predatory Behavior and Evolution of the Enigmatic Taxon. N. Jb. Geol. Palaeont. Abh. 2134 (3): 355-74

• Maisch, M. W. & Matzke, A. T. (2000) The ichthyosauria. Stuttgarter Beitraege zur Naturkunde. Serie B. Geologie und Palaeontologie. 2000; (298): 1-159.

• McGowan, Christopher (1992) Dinosaurs, Spitfires and Sea Dragons, Harvard University Press, ISBN 067420770X

• Motani, R. (1997), Temporal and spatial distribution of tooth implantation in ichthyosaurs, in JM Callaway & EL Nicholls (eds.), Ancient Marine Reptiles. Academic Press. pp. 81-103.

• Motani, R. (2000), Rulers of the Jurassic Seas, Scientific American vol.283, no. 6

• Motani, R., Minoura, N. & Ando, T. (1998), Ichthyosaurian relationships illuminated by new primitive skeletons from Japan. Nature 393: 255-257.

• Motani, R., Manabe, M., and Dong, Z-M, (1999) The status of Himalayasaurus tibetensis (Ichthyopterygia) pdf, Paludicola2(2):174-181 June 1999

• Nicholls, E. L. & Manabe, M. 2001. A new genus of ichthyosaur from the Late Triassic Pardonet Formation of British Columbia: bridging the Triassic-Jurassic gap. Canadian Journal of Earth Sciences 38, 983-1002.

Scientific American is one of the oldest and most serious popular-science magazines. ...

External links

• USMP Berkeley's ichthyosaur introduction
• Ryosuke Motani's detailed Ichthyosaur homepage, with vivid graphics
• Eureptilia: Ichthyosauria - Palaeos
• Ichthyosauria - cladogram (Mikko's Phylogeny Archive)