Cast of the first known completeIchthyosaurus specimen (originally referred to asProteosaurus), which was destroyed duringWW2
Ichthyosaurus was the first complete fossil to be discovered in the early 19th century byMary Anning inEngland;[9] the holotype ofI. communis, no coll. number given,[10] was a fairly complete specimen discovered by Mary and Joseph Anning around 1814 inLyme Regis[11] but was reported as lost by McGowan (1974) in his review of the latipinnateichthyosaurs ofEngland.[12] The nameIchthyosaurus was first used byCharles König in 1818, but it was not used in a formal scientific description, with the earliest described ichthyosaur beingProteosaurus by James Everard Home in 1819 for a skeleton which is now attributed toTemnodontosaurus platyodon.Henry De la Beche andWilliam Conybeare in 1821 consideredIchthyosaurus to havetaxonomic priority overProteosaurus and named the speciesI. communis based on BMNH 2149 (now NHMUK PV R1158), a now partially lost specimen now assigned toTemnodontosaurus that was discovered and collected between 1811 and 1812.[13][14] One specimen that Home had assigned toProteosaurus was the first complete ichthyosaur skeleton known, but it was destroyed in WW2. Two casts were rediscovered in 2022, showing that the specimen belonged toIchthyosaurus, but of uncertain species.[15] During the 19th century, almost all fossil ichthyosaurs were attributed toIchthyosaurus, resulting in the genus having over 50 species by 1900. These species were subsequently moved to separate genera orsynonymised with other species.[16]
Ichthyosaurus was smaller than most of its relatives, with the largest specimen ofI. somersetensis measuring up to 3–3.3 m (9.8–10.8 ft) in length.[19] In comparison, other species were much smaller, with theI. communis reaching up to 2 metres (6.6 ft) in length,I. larkini probably up to 2.5 metres (8.2 ft),I. anningae up to 1.8 metres (5.9 ft),I. breviceps up to 1.9 metres (6.2 ft), andI. conybeari up to 1.5 metres (4.9 ft).[1][10] ManyIchthyosaurus fossils are well-preserved and fully articulated. Some fossils still had baby specimens inside them, indicating thatIchthyosaurus wasviviparous. Similar finds in the relatedStenopterygius also show this.[20][21] Jurassic ichthyosaurs had a fleshydorsal fin on their back as well as a largecaudal fin.Icthyosaurus is distinguished from other ichthyosaurs by having a wide forefin with 5 or more digits with an anterior digital bifurcation, but the morphology of thehumerus andcoracoids are also distinct from that of other Lower Jurassic ichthyosaurs, as is the arrangement of thedermal bones, though thesuture lines used to diagnose these are not always visible.[16]
Ichthyosaurus is suggested to have been aram feeder, with the morphology of its hyobranchial apparatus suggesting that it was incapable ofsuction feeding,[24] using the jaws and teeth alone to capture prey.Ichthyosaurus is thought to have been a pursuit predator that was capable of sustained swift swimming viathunniform locomotion.[25] Stomach contents ofIchthyosaurus anningae indicate that it fed oncephalopods (likelybelemnites) and fish.[26] Like other ichthyosaurs, it likely relied on its sense of sight, possibly in combination witholfaction.[27]
It was initially believed thatIchthyosaurus laid eggs on land, but fossil evidence shows that in fact the females gave birth to live young. As such, they were well-adapted to life as fully pelagic organisms (i.e. they never came onto land). Three pregnant females are known, all of the subspeciesI. somersetensis. Although none of the fetuses show a clear birth orientation it is likely they exited tail-first, a common feature in highly aquatic vertebrates.[20]
^Dean R. Lomax (2010). "AnIchthyosaurus (Reptilia, Ichthyosauria) with gastric contents from Charmouth, England: First report of the genus from the Pliensbachian".Paludicola.8 (1):22–36.
^Maisch MW, Matzke AT. 2000. The Ichthyosauria.Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie)298: 1-159
^McGowan C, Motani R. 2003. Ichthyopterygia. – In: Sues, H.-D. (ed.):Handbook of Paleoherpetology, Part 8, Verlag Dr. Friedrich Pfeil, 175 pp., 101 figs., 19 plts; München
^abJudy A. Massare &Dean R. Lomax (2018). A taxonomic reassessment ofIchthyosaurus communis andI. intermedius and a revised diagnosis for the genus,Journal of Systematic Palaeontology, 16:3, 263-277, DOI: 10.1080/14772019.2017.129111
^Home, E. (1814). Some account of the fossil remains of an animal more nearly allied to fishes than any other classes of animals.Philosophical Transactions of the Royal Society of London, 101, 571–577.
^McGowan, C. (1974). A revision of the latipinnate ichthyosaurs of the Lower Jurassic of England (Reptilia: Ichthyosauria).Life Science Contributions of the Royal Ontario Museum 100:1–30
^De la Beche, H. T. & W. D. Conybeare. (1821). Notice of the discovery of a new fossil animal, forming a link between theIchthyosaurus and crocodile, together with general remarks on the osteology of theIchthyosaurus.Transactions of the Geological Society of London 5: 559–594.
^Conybeare, W. D. (1822). Additional notices on the fossil generaIchthyosaurus andPlesiosaurus.Transactions of the Geological Society of London, 1, 103–123.
^abBöttcher R. 1990. Neue Erkenntnisse über die Fortpflanzungsbiologie der Ichthyosaurier.Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie)164: 1-51
^Martill D.M. 1993. Soupy Substrates: A Medium for the Exceptional Preservation of Ichthyosaurs of the Posidonia Shale (Lower Jurassic) of Germany.Kaupia - Darmstädter Beiträge zur Naturgeschichte2: 77-97
^Druckenmiller, P. M.; Maxwell, E. E. (2010). "A new Lower Cretaceous (lower Albian) ichthyosaur genus from the Clearwater Formation, Alberta, Canada".Canadian Journal of Earth Sciences.47 (8):1037–1053.Bibcode:2010CaJES..47.1037D.doi:10.1139/E10-028.
^abArkhangel'sky, M. S., 1998, On the Ichthyosaurian Genus Platypterygius: Palaeontological Journal, v. 32, n. 6, p. 611-615.
