Dacentrurus armatus Owen, 1875

Sánchez-Fenollosa, Sergio & Cobos, Alberto, 2025, New insights into the phylogeny and skull evolution of stegosaurian dinosaurs: An extraordinary cranium from the European Late Jurassic (Dinosauria: Stegosauria), Vertebrate Zoology 75, pp. 147-171 : 147-171

publication ID	https://doi.org/10.3897/vz.75.e146618
publication LSID	lsid:zoobank.org:pub:2B64FEC4-268A-4840-9FD4-E2F8C42F3475
DOI	https://doi.org/10.5281/zenodo.15516929
persistent identifier	https://treatment.plazi.org/id/F73F2FB4-C609-5069-B77B-62FB2EEBA30D
treatment provided by	Vertebrate Zoology by Pensoft
scientific name	Dacentrurus armatus Owen, 1875
status

Treatment

Synonymy.

Omosaurus armatus Owen, 1875 , Stegosaurus armatus Lydekker, 1888 , Omosaurus lennieri Nopcsa, 1911 b , Dacentrurus lennieri Hennig, 1915 b , Dacentrurosaurus armatus Hennig, 1925 , Miragaia longicollum Mateus, Maidment & Christiansen, 2009 , and Dacentrurus longicollum Raven & Maidment, 2017 .

Revised diagnosis.

D. armatus possesses the following autapomorphies (modified from Sánchez-Fenollosa et al. 2025): A premaxilla with (1) an anterior tip that drawn into a point; and (2) an anterolateral margin ventrally projected; a supraoccipital with (3) a posteroventrally orientation with an angle greater than 90 ° with the dorsal plane of the skull roof (new); a cervical series with (4) at least 17 cervical vertebrae; and (5) at least anterior and mid cervical ribs fused to the vertebrae; cervical vertebrae with (6) two spinopostzygapophyseal laminae that extend anterolaterally from the top of the postzygapophyses to both sides of the base of the neural spine and culminate on its anterior margin; mid and posterior cervical vertebrae with (7) neural spines positioned in the anterior half of the centrum; anterior caudal vertebrae with (8) short neural spines and expanded and rounded apices; an ilium with (9) a wide and short preacetabular process; and (10) a broad base of the preacetabular process and a smooth curvature between the anterior margin of the sacral yoke and the dorsal margin of the preacetabular process; and a pubis with (11) a dorsoventrally expanded anterior end of the prepubis.

Holotype.

NHMUK PV OR 46013 ( Owen 1875; Galton 1985).

Type locality and horizon.

Unknown horizon. The fossils were discovered in a clay pit at the municipality of Swindon ( United Kingdom). Lower part of the Kimmeridge Clay Formation, Upper Jurassic (Kimmeridgian) ( Davies 1876; Galton 1985; Martill et al. 2006).

Referred material.

A partial cranium (MAP- 9029) (Figs 2 View Figure 2 , 3 View Figure 3 ) and a mid cervical vertebra (MAP- 9030) (Fig. 4 View Figure 4 ). Additional postcranial fossils of this specimen were recovered, but their study is beyond the scope of this research and some of them are still unprepared.

Other referred material.

MHNH A ( Nopcsa 1911 b; Galton 1990), ML 433 (Fig. 6 A – G View Figure 6 ; Mateus et al. 2009), ML 433 - A ( Mateus et al. 2009), MG 4863 ( Costa and Mateus 2019), the Pedras Muitas specimen ( Galton 1991; Escaso 2014), the Murteiras specimen ( Galton 1991; Escaso 2014), the Atalaia specimen ( Galton 1991; Escaso 2014), SHN. LPP 016 ( Escaso et al. 2007 b), the CO specimen ( Casanovas-Cladellas et al. 1995), the RD- 10 specimens ( Cobos et al. 2010; Sánchez-Fenollosa et al. 2022), and the CT- 28 specimen ( Sánchez-Fenollosa et al. 2025).

Locality and horizon.

Están de Colón (RD- 34) site in the municipality of Riodeva, province of Teruel, Aragón, Spain. South-Iberian Basin, Villar del Arzobispo Formation, Upper Jurassic (upper Kimmeridgian – Tithonian) (Fig. 1 View Figure 1 ).

Locality and horizon of other referred material.

All specimens are known from the Upper Jurassic (Kimmeridgian – Tithonian) of western Europe ( France, Portugal, and Spain) ( Sánchez-Fenollosa et al. 2025 and references therein).

Systematic remarks.

This stegosaurian specimen is classified as D. armatus because it possesses characters 5, 6, and 7 from the diagnosis. When coded as an independent OTU, it was recovered as sister to D. armatus in the phylogenetic analyses (File S 1 [fig. S 1]).

Description.

Cranium (MAP- 9029) (Figs 2 View Figure 2 , 3 View Figure 3 ). MAP- 9029 consist of the posterior half of the skull roof including a fragment of the right prefrontal, both frontals, both postorbitals, both squamosals, the parietal, the supraoccipital, and a possible fragment of the left paroccipital process (Figs 2 View Figure 2 , 3 View Figure 3 ). The dorsal surface is slightly eroded and exhibits some cortical remodelling (Figs 2 A View Figure 2 , 3 A View Figure 3 ). Perhaps for these reasons, sutures between elements are barely visible. Two small and open supratemporal fenestrae are present (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). Lateral temporal fenestrae presumably are large. Ventrally it is strongly eroded including almost all the braincase (Figs 2 View Figure 2 , 3 View Figure 3 ). Each element of the cranium will be described individually below. — Prefrontal. A small fragment of the right prefrontal can be observed in posteromedially contact to the frontal (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). The suture with the frontal is barely visible (Figs 2 View Figure 2 , 3 B View Figure 3 ). Its surface is flat and smooth (Figs 2 A View Figure 2 , 3 A View Figure 3 ). Presumably, the non-preserved supraorbitals would exclude the prefrontal (also the frontal) from the orbital rim similar to that in other stegosaurs (e. g., Sereno and Dong 1992; Galton and Upchurch 2004; Salgado et al. 2017; Maidment et al. 2018; pers. obs. [ NHMUK PV R 36730 View Materials ]). — Frontal. Both frontals are present and they are longer than wide (Figs 2 A View Figure 2 , 3 A, B View Figure 3 ) similar to that in S. stenops ( Galton and Upchurch 2004; pers. obs. [ NHMUK PV R 36730 View Materials ]). Their surfaces are flat and the sagittal suture between them is straight and slightly convex (Figs 2 A View Figure 2 , 3 A, B View Figure 3 ). The suture with postorbitals and parietal is barely visible in dorsal view (Figs 2 A View Figure 2 , 3 A, B View Figure 3 ). — Postorbital. Both almost complete postorbitals are preserved and they form the anterolateral margins of the supratemporal fenestrae (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). The medial process is flat, broad and sutured to the frontal and parietal (excluding the frontal from the anteromedial margin of the supratemporal fenestra) (Figs 2 View Figure 2 , 3 A – D View Figure 3 ) similar to that in S. stenops ( Galton and Upchurch 2004; pers. obs. [ NHMUK PV R 36730 View Materials ]). The posterior process is slender and D-shaped in cross-section with a convex dorsal surface and a flattened ventral surface (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). The posterior process is in contact to the squamosal (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). The right postorbital preserves the most proximal part of the ventral process (Figs 2 B View Figure 2 , 3 C View Figure 3 ) and dorsally in this area the postorbital is bulbous and exhibits a very small horn-like protuberance (Figs 2 A View Figure 2 , 3 A View Figure 3 ). It is different from the bigger and more medially located protuberance of H. taibaii ( Sereno and Dong 1992) . — Squamosal. Both squamosals are present and triradiate (Figs 2 View Figure 2 , 3 View Figure 3 ). They form the posterior margin of the supratemporal fenestrae and are in contact with the postorbital, parietal, and occiput (Figs 2 View Figure 2 , 3 View Figure 3 ). The anterior process is short (Figs 2 View Figure 2 , 3 A – D View Figure 3 ) and in the left squamosal it can be seen to underlap the postorbital (Figs 2 B, C View Figure 2 ). The posterior process is well-developed and horn-like (Figs 2 View Figure 2 , 3 View Figure 3 ). In dorsal and ventral views, the lateral margin between posterior processes of postorbital and squamosal is concave (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). — Parietal. The parietal forms the medial margin of the supratemporal fenestrae (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). It is sub-square in dorsal view and its dorsal surface is convex with a straight and pronounced sagittal crest (Figs 2 A View Figure 2 , 3 A, B View Figure 3 ) similar to that in T. multispinus ( Dong et al. 1983) . Distinct breaks in slope separate the dorsal surface from the lateral surfaces and the occiput (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). — Occiput. The upper-most part of the occiput is preserved and sutures between elements cannot be observed (Fig. 3 E, F View Figure 3 ). The surface of the supraoccipital is smooth and there is not a dorsoventral ridge (Figs 2 A View Figure 2 , 3 E, F View Figure 3 ) similar to that in K. aethiopicus ( Galton 1988) . The supraoccipital is obliquely oriented with an angle greater than 90 ° with the dorsal plane of the skull roof (Figs 2 View Figure 2 , 3 A – D View Figure 3 ). A possible fragment of the left paroccipital process is preserved (Fig. 3 E, F View Figure 3 ).

Cervical vertebra (MAP- 9030) (Fig. 4 View Figure 4 ). MAP- 9030 is an almost complete mid cervical vertebra (Fig. 4 View Figure 4 ). It is distorted and the anterior-most part is missing; therefore, some features and measurements must be considered cautiously. The centrum is presumably amphicoelous (Fig. 4 C View Figure 4 ) and longer than wide and tall (File S 1 [table S 1]). The articular facets are wider than tall (File S 1 [table S 1]) and heart-shaped (Fig. 4 A, C View Figure 4 ). Smooth concentric ridges are present in the surface of the posterior articular facet (Fig. 4 C View Figure 4 ). Laterally, the parapophyses are located in the anterior margin and the upper half of the centrum (Fig. 4 A, B, E View Figure 4 ). The ventral surface is smooth and concave due to the distortion (Fig. 4 E View Figure 4 ). In general, the neural arch is anteroposteriorly elongated and dorsally short (Fig. 4 A – D View Figure 4 ). The neural canal is large and suboval (Fig. 4 A, C View Figure 4 ). Regarding the prezygapophyses, only the posterior-most region is preserved and located below the postzygapophyses (Fig. 4 A, B, D View Figure 4 ). The diapophyses arise on the neural arch ventral to the prezygapophyses (Fig. 4 A – C View Figure 4 ). Both cervical ribs are preserved and fused to the parapophyses and diapophyses of the vertebra (Fig. 4 View Figure 4 ) similar to that in D. armatus ( Casanovas-Cladellas et al. 1995; Galton 1991; Mateus et al. 2009; Cobos et al. 2010; Costa and Mateus 2019; pers. obs. [ ML 433 and CO specimen]), although only the left one is well-preserved (Fig. 4 B View Figure 4 ). The left cervical rib is posteriorly directed, medially curved, notably overhang the centrum and has a blunt and round tip (Fig. 4 B, D, E View Figure 4 ). The postzygapophyses are finger-like and extend beyond the posterior articular facet of the centrum (Fig. 4 B – D View Figure 4 ). This differs from the greatly elongated postzygapophyses of S. stenops ( Ostrom and McIntosh 1966; Escaso et al. 2007 a; Maidment et al. 2015). Their articular facets are lateroventrally directed and oval in outline (Fig. 4 B, C View Figure 4 ). Dorsally, two spinopostzygapophyseal laminae are well-visible, wide, and extending anterolaterally from the top of the postzygapophyses to both sides of the base of the neural spine and culminate on its anterior margin (Fig. 4 D View Figure 4 ). This condition is shared with D. armatus ( Mateus et al. 2009; Costa and Mateus 2019; pers. obs. [ ML 433 and CO specimen]), but not with other stegosaurs ( Ostrom and McIntosh 1966; Maidment et al. 2015; 2018; 2020; pers. obs. [ NHMUK PV R 37367 and NHMUK PV R 37368]). The neural spine is located in the anterior half of the vertebra (Fig. 4 B View Figure 4 ) and it is short and slightly transversely expanded (Fig. 4 A, C View Figure 4 ) similar to that in D. armatus ( Casanovas-Cladellas et al. 1995; Mateus et al. 2009; Costa and Mateus 2019; pers. obs. [ ML 433 and CO specimen]). However, it is in the posterior half of the centrum ( Gilmore 1914; Hennig 1925; Ostrom and McIntosh 1966; Dong et al. 1983; Zhou 1984; Galton 1990; Carpenter et al. 2001; Escaso et al. 2007 a; Jia et al. 2007; Maidment et al. 2015; 2018) or in both halves ( Maidment et al. 2020; pers. obs. [ NHMUK PV R 37367 and NHMUK PV R 37368]) in other stegosaurian species.