Considerations on the replacement of a type species in the case of the sauropod dinosaur Diplodocus Marsh, 1878

Abstract

The sauropod dinosaur genus Diplodocus Marsh, 1878, is currently typified by a morphologically undiagnosable type species, D. longus Marsh, 1878. Only two caudal vertebrae and an associated partial chevron of its holotype (Yale Peabody Museum [YPM] VP.001920) remain reasonably complete, but more, fragmentary caudal vertebrae are available, and provide additional morphological information. YPM VP.001920 can be referred to Diplodocus generally, but cannot be distinguished from other Diplodocus species based on autapomorphies. Thus, the genus Diplodocus would have to be considered a nomen dubium. In order to resolve this unsatisfactory taxonomic issue, Tschopp and Mateus (2016) proposed to designate a new type species for the genus Diplodocus: namely, the well-known D. carnegii Hatcher, 1901.
Herein, we expand upon historical and taxonomic issues concerning the holotype of D. longus, in order to: (1) provide additional imagery and information on the specimen and (2) to address comments against the replacement of D. longus by D. carnegii as the type species of Diplodocus as proposed by Tschopp and Mateus (2016).