International Commission on Zoological Nomenclature

Case 3536

Overview

Case 3536: Stegosaurus Marsh, 1877 (Dinosauria, Ornithischia): proposed replacement of the type species with Stegosaurus stenops Marsh, 1887

Publication Type:Journal Article
Year of Publication:2011
Authors: Galton, P. M.
Journal:Bulletin of Zoological Nomenclature
Volume:68
Issue:2
Start Page:127
Pagination:127-133
Date Published:06/2011
Type of Article:Case
Keywords: Dinosauria, Nomenclature, Ornithischia, S. armatus, S. stenops, Stegosauria, Stegosauridae, Stegosaurinae, Stegosaurus, taxonomy, Upper J, Western U.S.A.
Abstract:The purpose of this application, under Article 81.1 of the Code, is to preserve stability in the taxonomy of stegosaurian dinosaurs by replacing Stegosaurus armatus Marsh, 1877, the unidentifiable type species of the ornithischian dinosaur genus Stegosaurus Marsh, 1877, with the very well represented nominal species Stegosaurus stenops Marsh, 1887, also from the Upper Jurassic Morrison Formation, U.S.A. This genus is the basis for Stegosauria Marsh, 1877, STEGOSAUROIDEA Marsh, 1880, STEGOSAURIDAE Marsh, 1880 and STEGOSAURINAE Marsh, 1880. Maidment et al. (2008) listed seven putative autapomorphic characters for Stegosaurus and five for the species Stegosaurus armatus in its current usage. However, the holotype of S. armatus, which consists of an articulated series of 18 incomplete vertebrae from the proximal half of the tail and a very large but incomplete dermal plate, shows none of these diagnostic characters and so S. armatus must be considered a nomen dubium. However, the holotype of S. stenops Marsh, 1887 shares all 12 autapomorphies with S. armatus in its current usage, being based on an almost complete skeleton (USNM 4934), most of it still in the rock preserving almost natural articulation, which would make S. stenops by far the best available species to replace S. armatus as type species of Stegosaurus Marsh, 1877.

Case:
Case 3536

Volume/Issue:
68(2)

Taxonomic Group(s):
Dinosauria

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Comments

Comments on Stegosaurus Marsh, 1877 (Dinosauria, Ornithischia): proposed replacement of the type species with Stegosaurus stenops Marsh, 1887 (Case 3536) 1
Publication Type:Journal Article
Year of Publication:2011
Authors: Maidment, S. C. R.
Journal:Bulletin of Zoological Nomenclature
Volume:68
Issue:3
Start Page:213
Pagination:213-214
Date Published:09/2011
Type of Article:Comment
Keywords:
Abstract: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.
Full Text:

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.

Case:
Case

Volume/Issue:
68(3)

Taxonomic Group(s):

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Comments on Stegosaurus Marsh, 1877 (Dinosauria, Ornithischia): proposed replacement of the type species with Stegosaurus stenops Marsh, 1887 (Case 3536) 2
Publication Type:Journal Article
Year of Publication:2011
Authors: Carpenter, K.
Journal:Bulletin of Zoological Nomenclature
Volume:68
Issue:3
Start Page:214
Pagination:214-215
Date Published:09/2011
Type of Article:Comment
Keywords:
Abstract:The taxon Stegosaurus armatus was established by O.C. Marsh in 1877 on a very fragmentary specimen from the Morrison Formation near Morrison, Colorado (erroneously stated to be ‘Morrison, Wyoming’ by Galton, BZN 68: 127). The specimen was encased in silicified sandstone and collected very poorly by modern standards using hammers and chisels, plus explosives to reduce the rock into more manageable pieces.
Full Text:

The taxon Stegosaurus armatus was established by O.C. Marsh in 1877 on a very fragmentary specimen from the Morrison Formation near Morrison, Colorado (erroneously stated to be ‘Morrison, Wyoming’ by Galton, BZN 68: 127). The specimen was encased in silicified sandstone and collected very poorly by modern standards using hammers and chisels, plus explosives to reduce the rock into more manageable pieces. The result is that much of the specimen was greatly damaged and many pieces missing, thus making it only marginally diagnostic (Carpenter & Galton, 2001), as noted by Galton (BZN 68: 130) in his petition. Such situations are unfortunately common for dinosaur specimens named during the 1800s that now require petitions to the Commission to ensure their stability (e.g. Case 3037, Charig & Chapman, 1998; Case 3506, Paul & Carpenter, 2010). In these examples, specimens displayed characters once thought to be unique but which were later found to be more widely distributed through the discovery of more complete specimens. Wilson & Upchurch (2003) refer to this as ‘historical obsolescence’. Stegosaurus armatus certainly falls into this category in that the hexangular caudal vertebrae and large, plate-like osteoderms were thought unique among the Dinosauria. However, subse- quent discoveries in Africa, Asia, Europe, and North America have shown that these characters occur in other taxa referred to the Stegosauria. As noted by Galton (BZN 68: 131), the type of S. armatus has no autapomorphic characters, therefore it cannot be separated from any other taxon of Stegosauria. In contrast to S. armatus, the nominal species Stegosaurus stenops Marsh, 1887 is represented by several nearly complete skeletons and thus is very well known. These specimens form the basis for the current concept of the genus Stegosaurus (Marsh, 1887, 1891; Gilmore, 1914; Carpenter & Galton, 2001; Carpenter et al., 2001; Galton & Upchurch, 2004; Maidment et al., 2008; Carpenter, 2010; Galton, 2010). Because Stegosaurus is such an iconic dinosaur, and because the name is so well entrenched in the scientific literature, its name should be associated with material of taxonomic utility. That such is not currently the case is shown by Maidment et al. (2008) declaring Hypsirophus discursus, Stegosaurus ungulatus, S. duplex, Diracodon laticeps, and Stegosaurus stenops to be junior synonyms of S. armatus. However, the result is the creation of a ‘superspecies’ showing a wider range of non-ontogenetic variation throughout the skeleton than any other species of Dinosauria, except waste-basket taxa (e.g., Iguanodon prior to Paul, 2008). As Carpenter (2010) has noted, the range of variation in S. armatus (sensu Maidment et al., 2008) cannot be replicated in other large samples of stegosaurids (e.g. Kentrosaurus aethiopicus from Africa), therefore casting doubt on the validity of the variations, which in turn casts doubt on the concept of S. armatus as defined by Maidment et al. (2008). All of this confusion would be eliminated by replacing the nominal species S. armatus with S. stenops as petitioned by Galton (BZN 68: 127–133), thereby ensuring taxonomic stability for the well-known genus Stegosaurus. Additional references Charig, A.J. & Chapman, S.D. 1998. Case 3037. Iguanodon Mantel, 1825 (Reptilia, Orni- thischia): proposed designation of Iguanodon bernissartensis Boulenger in Beneden, 1881 as the type species, and proposed designation of a lectotype. Bulletin of Zoological Nomenclature, 55(2): 99–104. Paul, G.S. 2008. A revised taxonomy of the iguanodont dinosaur genera and species. Cretaceous Research, 29, 192–216. Paul, G.S. & Carpenter, K. 2010. Case 3506. Allosaurus Marsh, 1877 (Dinosauria, Theropoda): proposed conservation of usage by designation of a neotype for its type species Allosaurus fragilis Marsh, 1877. Bulletin of Zoological Nomenclature, 67(1): 1–4. Wilson, J.A. & Upchurch, P. 2003. A revision of Titanosaurus Lydekker (Dinosauria – Sauropoda), the first dinosaur genus with a ‘Gondwanan’ distribution. Journal of Systematic Palaeontology, 1: 125–160.

Case:
Case

Volume/Issue:
68(3)

Taxonomic Group(s):

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Status of Case:
Open Cases


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