Dacentrurus sp.
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publication ID |
https://doi.org/ 10.5252/geodiversitas2022v44a25 |
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publication LSID |
urn:lsid:zoobank.org:pub:EA12DCB7-A5BE-4763-B805-25087EBD726D |
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DOI |
https://doi.org/10.5281/zenodo.6928915 |
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persistent identifier |
https://treatment.plazi.org/id/03C887B9-FF97-FFCA-7455-A0CEFA44F85D |
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treatment provided by |
Felipe |
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scientific name |
Dacentrurus sp. |
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( Fig. 23 View FIG D-J)
DESCRIPTION
Stegosaurs are represented at Angeac-Charente by 84 identified skeletal elements, most of which are vertebrae and ribs. Other remains include a few appendicular (phalanges) and skull (squamosal and braincase elements) bones, and one tooth ( Fig. 23 View FIG D-J). Except for the tooth, which was collected following washing and screening, all the other elements are from the same area ( Fig. 3 View FIG [CG4 to CG7 plots]). They very likely belong to the same individual because none of the identified bones represent the same skeletal element. Moreover, the relative proportion of the bones is also consistent with their belonging to a single individual, as suggested by the reconstructed vertebral series ( Fig. 23 View FIG F-J).
The single collected dentary tooth crown ( Fig. 23D, E View FIG ) has the same proportions as the stegosaur tooth from Chervesde-Cognac described by Billon-Bruyat et al. (2010). It has a preserved height of 4.2 mm and a maximum mesiodistal width basally of 4 mm. The root is broken at its base. The presence of a sharp demarcation, either swelling or cingulum, almost at the same level on each crown surface together with the mesiodistal symmetry of the tooth lead us to refer this tooth to a stegosaurian (Billon-Bruyat et al. 2010). Nevertheless, the morphology of the crown is quite distinct from that of other known stegosaur teeth. As in Huayangosaurus , the base of the crown is sharply differentiated from the root by a prominent swelling, but there is no true ring-shaped cingulum as in other stegosaurs ( Sereno & Dong 1992). In labial view, a single rounded median protuberance is present, but there are no well-defined ridges. A broad, 45° angled wear surface is present above the bulbous crown base on the labial side and has truncated a part of the dentary crown, so that the denticles are no longer visible ( Fig. 23D View FIG ). Vertical coarse ridges, semicircular in cross section and divided by narrow grooves are visible in lingual view.
A dozen cervical vertebrae, including the axis as well as four dorsal and two caudal vertebrae have been collected ( Fig. 23 View FIG F-J). The neural arches are often broken, probably due to trampling ( Rozada et al. 2021), and numerous neural spines or transverse processes are found isolated. The axial skeleton shows some features permitting clarification of the phylogenetic position of the Angeac-Charente stegosaur. The transverse processes of dorsal vertebrae project at a high angle to the horizontal as in all Thyreophoroidea ( Fig. 23I View FIG ), and the prezygapophyses are fused on some dorsal vertebrae as in most Eurypoda. The dorsal centra are wider than long (ANG 15-3937, centrum witdh 126 mm; centrum length 95 mm). This is a feature diagnostic of Dacentrurus according to Galton (1985) and Maidment et al. (2008), and of Dacentrurinae ( Dacentrurus + Miragaia ) ( Mateus et al. 2009; Costa & Mateus 2019). Cervical ribs are fused to para– and diapophyses in at least two cervical vertebrae. This feature is also diagnostic of Dacentrurinae ( Mateus et al. 2009; Costa & Mateus 2019).
A taxonomic revision of the Late Jurassic to Early Cretaceous European stegosaurs is beyond the scope of this paper. However, if we acknowledge the existence of several species of stegosaurs closely related to Dacentrurus ( Costa & Mateus 2019), we concur with Cobos et al. (2010) that, given the available diagnostic characters, and despite the discovery of a new specimen of Miragaia ( Costa & Mateus 2019), Dacentrurus and Miragaia cannot be clearly differentiated at a generic level, at this time. Moreover, we do not understand the taxonomical logic of creating, on the one hand the new European genus, Miragaia , and the new sub-family Dacentrurinae , while the original diagnostic characters of Dacentrurus , such as dorsal vertebral centra that are wider transversely than they are long anteroposteriorly (see Galton 1985; Maidment et al. 2008), largely encompass Miragaia , and on the other hand, synonymizing a third American genus Alcovasaurus with Miragaia ( Costa & Mateus 2019). Pending the complete description and revision of the Late Jurassic to Early Cretaceous European stegosaur material and a phylogenetic analysis of the specimens concerned, we still prefer to synonymize Miragaia with Dacentrurus ( Cobos et al. 2010) , which is not incompatible with the results of phylogenetic analyses ( Raven & Maidment 2017). Thus, based on Costa & Mateus (2019), the Angeac-Charente stegosaur may be more closely related to Dacentrurus longicollum (comb. nov.), because the cervical transverse processes of a posterior cervical vertebra project ventral to the ventral margin of the prezygapophyses. Nevertheless, it is very difficult to assess the condition of this feature in D. armatus , given that only one half of a neural arch is preserved in the type species ( Owen 1875; Galton 1985). In any case, the Angeac-Charente taxon is closely related to the English, Spanish and Portuguese stegosaurs, and it is the youngest occurrence of Dacentrurus . In addition to bony remains, about 100 stegosaur natural track casts in a range of sizes have been identified and documented on a single bedding plane in the CG3 plot, and assign to the ichnotaxon Deltapodus ( Rozada 2019; Rozada et al. 2021).
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