Ichthyosaurus De la Beche & Conybeare 1821
Creators: name: Massare, Judy A.
name: Lomax, Dean R.
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Ichthyosauria
Ichthyosauridae
Ichthyosaurus

description: Genus Ichthyosaurus De la Beche & Conybeare, 1821
1818 Ichthyosaurus Konig: 54 [nomen nudum].
1819a Proteosaurus Home: 209.
1821 Ichthyosaurus De la Beche & Conybeare: 563.
1840 Polyostinus Hawkins: 12.
1840 Paramecostinus Hawkins: 15.
1904 Eurypterygius Jaekel: 32.
1979 Protoichthyosaurus Appleby: 492 [in part].
Emended diagnosis. Pineal enclosed within frontals at their posterior edge; large, wide nasals; maxilla excluded from margin of the external naris by subnarial process of premaxilla and anterior process of lacrimal; squamosal present; basioccipital with extensive extracondylar area and well-developed peg; angular with minimal exposure in lateral view; scapula with long shaft, slightly expanded distal end and expanded proximal end, but acromion process absent; coracoid with prominent anterior and posterior notches; humerus with nearly equal width distally and proximally, with slight constriction in the shaft; forefin with distal carpals 3 and 4 contacting the intermedium; metacarpal 5 in the distal carpal row, in contact with the ulnare; digit V as prominent or more prominent than digit IV; digital bifurcation anterior to the primary axis in forefin; forefin with at least five primary digits (although the fin must be preserved to at least p4 row to verify that a bifurcation is present); hind fin with at least four primary digits and an anterior digital bifurcation; rectangular, closely spaced phalanges on most of proximal to middle portion of forefin; pelvic girdle tripartite, without fusion between pubis and ischium; femur longer than wide, with distal end wider than proximal end; preflexural vertebrae <80 (modified from McGowan & Motani 2003; Ji et al. 2016).
Occurrence. The genus is very common from Dorset and Somerset, England, but additional unequivocal occurrences of the genus include: Leicestershire (Martin et al. 1986), Nottinghamshire (Lomax & Gibson 2015), Warwickshire (Smith & Radley 2007), Gloucestershire (e.g. BU 5289, formerly BIRUG 4175), Worcestershire (WOSMG:1, WOSMG:2), Yorkshire (Maisch 1997; Massare et al. 2015), Devon (NHMUK PV R5787), England; Glamorgan, Wales (NMW 2009.35G.1); County Antrim, Northern Ireland (e.g. BELUM K1643, BELUM K28052); Belgium (Godefroit 1996); Switzerland (Maisch et al. 2008); Portugal (Zbyszewski & Moitinho de Almeida 1952; Bardet et al. 2008); and Alberta, Canada (McGowan 1978). The genus was also reported from Scotland, but contrary to Brusatte et al. (2015), these specimens (teeth and an impression of a lower jaw) are too fragmentary to be assigned to the genus. Similarly, a specimen from British Columbia, Canada (Dennison et al. 1990) shows no diagnostic characters of the genus, and the relative rostrum length would suggest that it is not Ichthyosaurus.
Ichthyosaurus has previously been reported from the uppermost Triassic (Rhaetian) of Somerset (McGowan & Motani 2003), but recent studies suggested that specimens from Somerset are probably from the lowermost Jurassic (Hettangian; Benson et al. 2012, 2015; Lomax & Massare 2017). However, DRL recently examined specimens of Ichthyosaurus currently held in a private collection that were collected in situ from the base of the Liassic Group (probably Rhaetian) of northern Somerset (Carpenter 2001). Thus it is plausible that some specimens of Ichthyosaurus in historical collections are from the Rhaetian. The genus has definitively been reported from the lowermost Jurassic (Hettangian), Pre- planorbis beds of Somerset and Leicestershire (McGowan 1974; Martin et al. 1986; also see discussion in Lomax & Massare 2017). The youngest occurrence of the genus is from the lower Pliensbachian (Lomax 2010; Lomax & Massare 2015).
description: Published as part of Massare, Judy A. & Lomax, Dean R., 2018, A taxonomic reassessment of Ichthyosaurus communis and I. intermedius and a revised diagnosis for the genus, pp. 263-277 in Journal of Systematic Palaeontology 16 (3) on pages 272-273, DOI: 10.1080/14772019.2017.1291116, http://zenodo.org/record/10883220