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In Case 3536, Galton outlined the taxonomic history of the iconic dinosaur genus Stegosaurus. In this Case, Galton asked the Commission to designate Stegosaurus stenops as type species of the genus Stegosaurus, thereby allowing the holotype specimen of Stegosaurus stenops, USNM 4934, to become the representative of the genus Stegosaurus.
The Case is complicated by the fact that those who have worked on the taxonomy of Stegosaurus do not agree about the taxonomic validity of various genera and species, as clearly outlined by Galton. In Case 3536 Galton suggested that the type specimen of Stegosaurus armatus (YPM 1850), which is the type species of Stego- saurus, bears no synapomorphies of Stegosaurus or autapomorphies of its own, making the name Stegosaurus armatus a nomen dubium. However, Mossbrucker et al. (2009) have suggested that YPM 1850 may bear an autapomorphy, making the name Stegosaurus armatus valid.
If YPM 1850 is undiagnostic, the generic name Stegosaurus is a nomen dubium. If YPM 1850 is diagnostic, as has been tentatively suggested by Mossbrucker et al. (2009), the name Stegosaurus armatus would likely be restricted to YPM 1850 because, as argued by Galton in the Case, YPM 1850 bears no other synapomorphies of Stegosaurus (in its current usage); thus all other material currently referred to the genus Stegosaurus would need a new generic name. Hypsirhophus discursus was named by Cope (1878) for a partial dorsal vertebra (AMNH 5731). Galton (2010) considered this specimen to be diagnostic and Hypsirhophus a distinct genus although for Maidment et al. (2008) and Maidment (2010) Hypsirhophus is the next available nominal genus to contain all other species of stegosaur formerly included in Stegosaurus.
Stegosaurus is one of the most iconic and most recognisable dinosaurs to both the public and scientists alike; the loss of the name Stegosaurus is therefore an unfavourable outcome.
Maidment et al. (2008) suggested that all stegosaur material from the Morrison Formation of the USA belonged to a single species (except for material described as Hesperosaurus mjosi by Carpenter et al. [2001]). Maidment et al. (2008) named this species Stegosaurus armatus, but diagnostic characters were based on a referred specimen, USNM 4934, the holotype of Stegosaurus stenops, which Maidment et al. (2008) considered to be a junior synonym of Stegosaurus armatus. Designating Stegosaurus stenops as the type species of Stegosaurus results in USNM 4934 being the specimen on which Stegosaurus is based. This is entirely appropriate because USNM 4934 is one of the most complete stegosaurs known from anywhere in the world, and the specimen has been used as the reference specimen against which other stegosaurs are compared since a detailed and definitive description of it was published (Gilmore, 1914). This is entirely in keeping with the work of Maidment et al. (2008), because USNM 4934 was used as the reference specimen in that work. As Galton has argued in the Case, it is more favourable to designate Stegosaurus stenops as the type species of Stegosaurus than to make USNM 4934 the type specimen of Stegosaurus armatus, because of the questions surrounding the presence or absence of diagnostic characters in the holotype of Stegosaurus armatus. By designating a new type species for Stegosaurus, problems of taxonomy relating to YPM 1850 are circumvented. I therefore fully support the proposal by Galton in Case 3536.
Comment:
Comment 3536-1
Volume/Issue:
68(3)
Taxonomic Group(s):
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