Ichthyosaurus was the first complete fossil to be discovered in the early 19th century by
Mary Anning in
England;[8] the holotype of I. communis, no coll. number given,[9] was a fairly complete specimen discovered by Mary and Joseph Anning around 1814 in
Lyme Regis[10] but was reported as lost by McGowan (1974) in his review of the latipinnate
ichthyosaurs of
England.[11] 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.[12][13] One specimen that Home had assigned to Proteosaurus was the first complete ichthyosaur skeleton known, but it was destroyed in WW2. Two casts were rediscovered in 2022, showing that the specimen belonged to Ichthyosaurus, but of uncertain species.[14] During the 19th century, almost all fossil ichthyosaurs were attributed to Ichthyosaurus, resulting in the genus having over 50 species by 1900. These species were subsequently moved to separate genera or
synonymised with other species.[15]
Ichthyosaurus was smaller than most of its relatives, with the largest specimen of I. somersetensis measuring up to 3–3.3 m (9.8–10.8 ft) in length.[18] In comparison, other species were much smaller, with the I. 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), and I. conybeari up to 1.5 metres (4.9 ft).[1][9] Many Ichthyosaurus fossils are well-preserved and fully articulated. Some fossils still had baby specimens inside them, indicating that Ichthyosaurus was
viviparous. Similar finds in the related Stenopterygius also show this.[19][20] Jurassic ichthyosaurs had a fleshy
dorsal fin on their back as well as a large
caudal 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 the
humerus and
coracoids are also distinct from that of other Lower Jurassic ichthyosaurs, as is the arrangement of the
dermal bones, though the
suture lines used to diagnose these are not always visible.[15]
Classification
This
cladogram below follows the topology from a 2010 analysis by Patrick S. Druckenmiller and Erin E. Maxwell.[21]
Ichthyosaurus is suggested to have been a
ram feeder, with the morphology of its hyobranchial apparatus suggesting that it was incapable of
suction feeding,[23] 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 via
thunniform locomotion.[24] Stomach contents of Ichthyosaurus anningae indicate that it fed on
cephalopods (likely
belemnites) and fish.[25] Like other ichthyosaurs, it likely relied on its sense of sight, possibly in combination with
olfaction.[26]
It was initially believed that Ichthyosaurus 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). The babies were born tail first to prevent them from drowning in the water.[19]
^
abDean R. Lomax; Judy A. Massare (2017). "Two new species of Ichthyosaurus from the lowermost Jurassic (Hettangian) of Somerset, England". Papers in Palaeontology. 3 (1): 1–20.
Bibcode:
2017PPal....3....1L.
doi:
10.1002/spp2.1065.
S2CID89567182.
^Dean R. Lomax (2010). "An Ichthyosaurus (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
^Maisch MW, Reisdorf AG, Schlatter R, Wetzel A. 2008. A large skull of Ichthyosaurus (Reptilia: Ichthyosauria) from the Lower Sinemurian (Lower Jurassic) of Frick (NW Switzerland). Swiss Journal of Geosciences101: 617-627.
^
abJudy A. Massare &
Dean R. Lomax (2018). A taxonomic reassessment of Ichthyosaurus communis and I. 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 the Ichthyosaurus and crocodile, together with general remarks on the osteology of the Ichthyosaurus. Transactions of the Geological Society of London 5: 559–594.
^Conybeare, W. D. (1822). Additional notices on the fossil genera Ichthyosaurus and Plesiosaurus. 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.