[7][8] Ichthyosaurus was the first complete fossil to be discovered in the early 19th century by Mary Anning in England;[9] the holotype of I. communis, no coll.

number given,[10] was a fairly complete specimen discovered by Mary and Joseph Anning around 1814 in Lyme Regis[11] but was reported as lost by McGowan (1974) in his review of the latipinnate ichthyosaurs of England.

[12] The name Ichthyosaurus was first used by Charles König in 1818, but it was not used in a formal scientific description, with the earliest described ichthyosaur being Proteosaurus by James Everard Home in 1819 for a skeleton which is now attributed to Temnodontosaurus platyodon.

Henry De la Beche and William Conybeare in 1821 considered Ichthyosaurus to have taxonomic priority over Proteosaurus and named the species I. communis based on BMNH 2149 (now NHMUK PV R1158), a now partially lost specimen now assigned to Temnodontosaurus that was discovered and collected between 1811 and 1812.

[27] It was initially believed that Ichthyosaurus laid eggs on land, but fossil evidence shows that in fact the females gave birth to live young.

Although none of the fetuses show a clear birth orientation it is likely they exited tail-first, a common feature in highly aquatic vertebrates.

[28] The poem has been translated among others by Charles Godfrey Leland[29] Some of the stanzas: The rushes are strangely rustling, The ocean uncannily gleams, As with tears in his eyes down gushing, An Ichthyosaurus swims.