Dinosaur skin impressions and associated skeletal remains from the upper Campanian of southwestern New Mexico: New data on the integument morphology of hadrosaurs

Skin impressions from the tail region of an indeterminate hadrosaur recentl y excavated from the Upper Cretaceous Ringbone Formation. southwest New Mex ico represent the first known dinosaur specimen from New Mexico with impres sions of the integument preserved in association with skeletal remains. The mid- to distal-caudal region is represented by 20 articulated centra, othe r disarticulated centra, a single chevron, ossified tendons and fragmentary bone, including poorly preserved neural spines. The skin impressions are preserved in negative and positive relief between two very fine-grained sandstone beds, interpreted as part of a fluvio-lacus trine facies package. The impression surface is directly below the ossified tendons, and 2.5 m from the articulated vertebral column. The skin impress ions are six discrete patches characterized by predominantly apical, circul ar to ovate tubercles. Measurements of the long and short axes of individua l tubercles demonstrate that a distribution of relatively homogenous tuberc le sizes occur along the tail section. The tubercles range from 3 to 12 mm and 10 to 16 mm on the short and long axes, respectively. All tubercles exa mined are ornamented with radiating ridges and grooves that converge at the ir apex. Presently, the material cannot be identified below the level of Ha drosauridae; however, a comparison of tubercle size, shape and ornamentatio n described previously from hadrosaur skin impressions indicates the integu ment morphology of the Ringbone hadrosaur has some similarities to that of the gryposaurs. In general, the complexity of the radial sculpturing, specifically the numb er of ridges and rugosity, increases with increasing tubercle size. This sp ecific type of ornamentation is not known from modern reptiles or birds; ho wever, the tubercular morphology is similar to that of the lizard Heloderma . Although it is impossible to determine whether the ridges and grooves may have had a physiologic function, these features would increase the surface area of the skin, and therefore may have afforded more efficient heat exch ange across the skin, or possibly provided added resistance to tearing and puncturing.