Iguanodon (Norman, 1980)

Norman, David B., 2015, On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna), Zoological Journal of the Linnean Society 173 (1), pp. 92-189 : 149-150

IGUANODON (? DAKOTADON ) LAKOTAENSIS WEISHAMPEL & BJORK, 1989

This taxon was recovered from the Lakota Formation (Barremian) of Lawrence County, South Dakota and comprises a major portion of an articulated skull of a large (∼ 8 m long) ornithopod .

Teeth and jaws

Individual dentary crowns exhibit a distally offset primary ridge that is paralleled by a lower, mesially offset secondary ridge; there is little evidence of tertiary (accessory) ridges as seen in Hypselospinus . Dentary teeth are very similar in appearance to those seen in both B. dawsoni and I. bernissartensis . Maxillary teeth are narrower than those of the dentary and display a very prominent primary ridge that is slightly distally offset and few, if any, tertiary (accessory) ridges. The anterior half of the lower jaw exhibits a stout ramus with a buccal emargination posteriorly. The predentary has a denticulate oral margin and a bilobed ventral process. The dentary shares only generalized features with what is known of the dentary of Hypselospinus .

Taxonomic note

The preserved skull of I. lakotaensis is similar in its proportions to that of I. bernissartensis (see below). Originally named I. lakotaensis in the description published by Weishampel & Bjork (1989), Paul (2008) proposed the new generic name Dakotadon on the basis of an emended diagnosis ( Paul, 2008: 199). The new diagnosis appears to contain a mixture of anatomy that is at variance with the original description and observations that are, at best, subjective in nature. As originally pointed out by Weishampel & Bjork (1989), the anatomy of the skull and dentition closely resembles that seen in I. bernissartensis . Anatomical differences: the pattern of sutures between the lacrimal, jugal, and maxilla on the posterior border of the antorbital fenestra; the single (rather than double) opening for cranial nerve VII on the lateral wall of the proötic; the structure of the supraoccipital (the absence of a median ridge). An additional difference, although not alluded to by Weishampel & Bjork (1989), is the comparatively low maxillary tooth position count (19). The structure of the supraoccipital was suspect- ed to be a preservational artefact and the incomplete nature of the neurocranial suturing further suggest- ed to the authors that this was a subadult individual; this latter factor may also explain the slightly reduced number of tooth positions.

Paul (2008) did not offer a valid reason for the new generic assignment of the holotype of I. lakotaensis and, on the basis of what is currently known this specimen, it would seem preferable to refer to this as cf. Iguanodon lakotaensis .