Table 1 in A taxonomic reassessment of Ichthyosaurus communis and I. intermedius and a revised diagnosis for the genus

Table 1. An assessment of previously proposed characters to distinguish Ichthyosaurus intermedius from I. communis. Additional details are in the text. Neotype refers to NHMUK PV R1162, the neotype of I. communis.
CharacterAuthorAssessmentBody lengthConybeare 1822; Owen 1840, 1881Inconsistent with historical identifications of specimens.Length of rostrumOwen 1840; Lydekker 1889Influenced by orientation and flattening; range overlaps among species.Tooth crown morphologyConybeare 1822; Owen 1840, 1881Intermediate forms exist; ontogenetic in part; influenced by orientation.Lack expanded tooth root; grooves not prominentOwen 1840, 1881No obvious difference from neotype.‘Waisted’ tooth formMaisch 1997Varies within an individual.Tooth countOwen 1840Uncertain taxonomic utility; depends on preparation and completeness in part.Number of maxillary teethOwen 1840; Maisch 1997Uncertain taxonomic utility; depends on preparation in part.Curvature of maxillary teeth under orbitMaisch 1997Occurs in other species; depends on orientation.Prominence of fossa on premaxilla, dentary, surangularMaisch 1997Uncertain taxonomic utility; range of variation has never been assessed.Extent of surangular versus angular, lateral viewConybeare 1822; Owen 1840No obvious difference from neotype.Relative length of mandibular symphysisOwen 1840Uncertain taxonomic utility; not commonly preserved so cannot be assessed.Relative contributions of dentary and splenials to mandibular symphysisOwen 1881Uncertain taxonomic utility; not commonly preserved so cannot be assessed.Morphology of maxillaMaisch 1997Noticeably lower, with shorter anterior process, on neotype.Morphology of jugal dorsal ramusMaisch 1997No obvious difference from neotype.Morphology of quadratojugalMaisch 1997No obvious difference from neotype.Clavicle morphologyOwen 1881; Lydekker 1889Highly variable within a species.Extent of humero-scapular articulation of coracoidOwen 1881Highly variable within a species.Forefin narrower with fewer phalangesOwen 1881; Lydekker 1889Highly variable; influenced by fin completeness and preparation.Notching on anterior digit of hind fin/ forefinLydekker 1889Little taxonomic utility; ontogenetic in part.Prominent vascular foramina in fin elementsLydekker 1889Little taxonomic utility; probably ontogenetic in part.Neural spine height on cervical and dorsal centraLydekker 1889Uncertain taxonomic utility; has never been assessed for most species.Number of presacral centraOwen 1840Similar in all species of Ichthyosaurus.