Abstract
Considered one of the best known flying reptiles, Pteranodon has been subject to several reviews in the last century. Found exclusively in the Upper Cretaceous Niobrara Formation and Pierre Shale Group 11 species have been attributed to this genus (excluding the ones presently regarded as representing Nyctosaurus). While reviewers agree that this number is inflated, there is disagreement on how many species can be identified. The last review recognized only two species (Pteranodon longiceps and Pteranodon sternbergi) both being sexually dimorphic. Based on several cranial features, some specimens previously referred to the genus Pteranodon are re-evaluated leading to the recognition of the following species, two of which new that are described here: Pteranodon longiceps, Geosternbergia sternbergi, Geosternbergia maiseyi sp. nov., and Dawndraco kanzai gen. et sp. nov. They differ mainly by features such as the direction and extension of the frontal crest, the angle and extension of the posterior process of the premaxillae, the shape and extension of the lower temporal fenestra and the length and proportion of the rostrum. The procedures to recognize a pterosaur species are also discussed here, and must take into account primarily morphology, in conjunction with stratigraphic and geographic data. Although well aware that changes in morphology not always reflect taxonomy, the lack of stratigraphic data and the limited number of specimens that can be confidently assigned to one species hampers our understanding on the morphological variations as a function of ontogeny, individual variation and sexual dimorphism. Although the present study has not eliminated the possibility to recognize such differences, caution is needed before models are generalized for pterosaurs.
Highlights
The pterodactyloid Pteranodon can be considered one of the best known flying reptiles
Besides the well-preserved holotype (YPM 1177, cast MN 6953-V), the most significant specimen of this species is FHSM VP 2183, first described by Miller (1972b). Pictures of this specimen shows the presence of a nutrient foramen on the dorsal side of the humerus, which Bennett (1994) observed in other humeri attributed to Pteranodon and is regarded as diagnostic for Pteranodon longiceps
Bennett (1994) has regarded KUVP 27821 as representing Pteranodon longiceps, but the morphological differences suggest that this material belongs to a distinct species closely related to Geosternbergia sternbergi
Summary
The pterodactyloid Pteranodon can be considered one of the best known flying reptiles. Pictures of this specimen shows the presence of a nutrient foramen on the dorsal side of the humerus, which Bennett (1994) observed in other humeri attributed to Pteranodon (not identified at a species level) and is regarded as diagnostic for Pteranodon longiceps It cannot be assured at this time that this feature is not present in Geosternbergia, to which no postcranial bone can be associated with confidence, or in Dawndraco kanzai gen. The holotype of Pteranodon longiceps (YPM 1177) shows an incomplete cranial crest, at the posterior margin, there is no marked anatomical difference between the comparable parts of YPM 1177 and YPM 2594, including the inclination of the quadrate Both specimens can be regarded as representing the same species (as indicated by Schoch 1984), and Pteranodon marshi should be considered as objective junior synonym of Pteranodon longiceps, as established by Bennett (1994). The quite large rostrum with sub-parallel dorsal and ventral margins argues against a placement of UALVP 24238 in Geosternbergia sternbergi
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