Temnodontosaurus (meaning "cutting-tooth lizard") is an extinct genus of large ichthyosaurs that lived during the Lower Jurassic in what is now Europe and possibly Chile.

The first known fossil is a specimen consisting of a complete skull and partial skeleton discovered on a cliff by Joseph and Mary Anning around the early 1810s in Dorset, England.

The anatomy of this specimen was subsequently analyzed in a series of articles written by Sir Everard Home between 1814 and 1819, making it the very first ichthyosaur to have been scientifically described.

[9][2]: 1  Around 1810,[a] a certain Joseph Anning discovered the first skull of the taxon on the cliffs of Black Ven, between the town of Lyme Regis and the village of Charmouth, two localities located in the county of Dorset, in the south of England.

[4][10][11][2]: 1 Beginning in 1814, Sir Everard Home wrote a series of six papers for the Royal Society describing the specimen, initially identifying it as a crocodile.

[12] Perplexed as to the real nature of the fossil, Home kept changing his mind about its classification, thinking that it would be a fish, then as an animal sharing affinities with the platypus, which was then recently described at that time.

[13] In 1821, Henry De la Beche and his colleague William Daniel Conybeare made the very first scientific description of Ichthyosaurus, but did not name any species.

[2]: 1  In their article, De la Beche and Conybeare refer several additional fossils discovered at Black Ven to this genus, also including the specimen originally described by Home, and finally identify it as a marine reptile.

[4][2]: 85  This specimen, already mentioned as a representative of the species by Richard Owen in 1881,[18]: 115–116  was originally discovered and partly collected by Mary Anning in July 1832 in Lyme Regis.

[27] The specific name comes from Ancient Greek τρίγωνον (trígônon, "triangle") and ὀδούς (odoús, "tooth"),[17]: 476, 714  in reference to the dental crown which is visibly triangular in this species.

[33] This classification has since been retained in subsequent works,[2]: 87  to the point that a large specimen discovered in England in 2021, nicknamed as the ‘Rutland Sea Dragon’, was even considered as the first probable representative within this country.

[7] In 1931, von Huene described a new species of the genus Leptopterygius, L. nürtingensis, based on a skull and some postcranial remains of a single specimen discovered in a quarry in the town of Nürtingen (hence its name), Baden-Württemberg, Germany.

[42][1]: 72  This specimen, cataloged as SMNS 13488, is mentioned for the first time in a work by Eberhard Fraas published posthumously in 1919, in which the author considers it to be the representative of an undetermined species of Ichthyosaurus.

[8] Although L. nürtingensis was only officially described in 1931 by von Huene,[42] the taxon was already mentioned a year earlier by the same author in an article concerning the ribs of the holotype specimen,[43] which have since been noted as lost.

[46] In 1997, Maisch and Axel Hungerbühler formally criticized McGowan's view, given that the holotype specimen is preserved in an excellent state of conservation and is easily diagnosable.

[44][7][34] In 1881, Owen attributed a large isolated skull discovered at Lyme Regis, cataloged as NHMUK PV R1157,[4][2]: 88  to the newly erected species of the genus Ichthyosaurus, I.

Although the specimen is mentioned in a detailed biostratigraphic analysis of the Lafarge quarries published in 1991,[47] it was in 2012 when the fossil, uncatalogued but stored in the Saint-Pierre-la-Palud local mining museum [fr], was officially designated as the holotype of the new species T. azerguensis by Jeremy E. Martin and his colleagues.

[49] A similar observation is shared in the study describing T. zetlandicus in 2022, with the authors mentioning these two species as too phylogenetically unstable to be included in a monophyletic grouping of Temnodontosaurus.

[7] In 1892, Albert Gaudry officially described a new species of Ichthyosaurus, I. burgundiae, on the basis of a specimen discovered in the quarries of the town of Sainte-Colombe, in Yonne, France.

[50] Even before the taxon was described by Gaudry, the specimen, being one of the largest ichthyosaurs known at the time, led to it being presented at the 1889 Paris Exposition, the same exhibition for which the Eiffel Tower was built.

[51] In 1974, McGowan described an additional species of Temnodontosaurus, T. risor, based on three skulls discovered at Lyme Regis, designating NHMUK PV R43971 as the holotype specimen.

[55] Temnodontosaurus, like other ichthyosaurs, had a long, thin snout, large eye sockets, and a tail fluke that was supported by vertebrae in the lower half.

[57] Temnodontosaurus is one of the largest ichthyosaurs identified to date, although the species which belong to it are not as imposing as Triassic forms like Shonisaurus, Himalayasaurus, Cymbospondylus or Ichthyotitan.

[59] In his extensive revision published in 1922, von Huene described a series of very imposing vertebrae from from the collections of the Banz Abbey Museum, Germany, the largest of them measuring 22 cm (8.7 in) high.

Based on SMNS 50000, a nearly complete skeleton of T. trigonodon, the author estimated the size of Banz's specimen at 16 m (52 ft) long,[53] as Huene initially suggested.

[67][7] Thus, pending future studies, Temnodontosaurus is currently seen as a wastebasket taxon including some large, more or less related neoichthyosaurians dating from the Lower Jurassic.

[6][7][25] In the last major study investigating the taxonomy of this genus, having been carried out by Laboury et al. (2022), only four species appear to form a monophyletic grouping, namely T. platyodon, T. trigonodon, T. zetlandicus and T.

[71] In Europe, Temnodontosaurus is mainly known from fossils dating from the various stages of the Lower Jurassic of England, Germany, France and Luxembourg,[4][53][2]: 87 [7] with nevertheless some more or less fragmentary specimens having been reported in Belgium,[2]: 83 [73] in Italy,[74] and in Switzerland.

This specimen, consisting of fragmentary remains of the jaws and catalogued since as SGO.PV.324, was later rediscovered in 2016 in the collections of the National Museum of Natural History of Chile in Santiago, and first described in 2020.

The presence of these taxa in northern Chile could be explained by an interfaunal exchange between Thetys and Panthalassa, although other evidence suggesting this remains thin.