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“Trachodon cantabrigiensis” possesses a unique character combination among basal hadrosauroids and hadrosaurids: the presence of a distally offset carina, the absence of secondary ridges, and the relatively short, wide tooth crown. However, the latter character is subject to variation depending on the position of the tooth within the tooth row: more mesially and distally positioned teeth in hadrosaurids often have lower crown height-to-width ratios than those in the middle of the tooth row (Gallimore and Evans, 2009). As the exact position of the holotype tooth within the tooth row cannot be established, we adopt a conservative approach and refrain from proposing a new generic name for this very limited material and regard the taxon as a nomen dubium (see also Horner et al., 2004). Nevertheless, it is likely that this single tooth, and possibly other isolated indeterminate material from the Cambridge Greensand Member (such as the isolated maxillary fragment described above), represents an otherwise unknown basal hadrosauroid taxon, given its geographic and stratigraphic provenance and its anatomical distinctiveness from other European hadrosauroids and more basally positioned iguanodontians.

6.3. Morphometric analysis of hadrosauroid tooth shape. (A) Principal component space defined by components 1 and 2; (B) principal component space defined by components 1 and 3; (C) UPGMA cluster analysis of hadrosauroid shape distances for the first four eigenvalue scores. Gray areas indicate shape spaces defined by Hadrosauridae.

‘Iguanodon’ hillii can be distinguished from “Trachodon cantabrigiensis” on the basis of its denticle morphology, suggesting that it, too, represents an otherwise unknown basal hadrosauroid taxon from the “middle” Cretaceous of England. However, the tooth possesses no autapomorphic features and as far as can be determined is similar in morphology to teeth of Telmatosaurus. We also regard this taxon as a nomen dubium (see also Horner et al., 2004).