Avetheropoda Paul, 1988

Malafaia, Elisabete, Mocho, Pedro, Escaso, Fernando, Narvaéz, Ivan & Ortega, Francisco, 2024, Taxonomic and stratigraphic update of the material historically attributed to Megalosaurus from Portugal, Acta Palaeontologica Polonica 69 (2), pp. 127-171 : 156

Avetheropoda Paul, 1988

Avetheropoda indet.

Fig. 22 .

Previous identifications: MG 4822 is labeled as belonging to Megalosaurus , but we have not found reference to this specimen in previous publications.

Material. —A small dorsal vertebra (MG 4822; Fig. 22 ) labeled as coming from Paimogo, in the municipality of Lourinhã ( Portugal) and probably comes from the Sobral Formation ( Fig. 2 ), which is Kimmeridgian–Tithonian in age ( Manuppella et al. 1999a).

Description.—The specimen is represented by the well-preserved centrum, but the neural arch is missing ( Fig. 22 ). It corresponds to a very small specimen, with 31 mm in length (see SOM 2). The centrum is spool-shaped in lateral view with strongly projected articular facets and is slightly elongated, being a little longer than high. There is a shallow depression in the lateral surface near the dorsal margin of the centrum. The neurocentral suture is open and extends along all the dorsal length of the centrum, slightly projecting into the lateral margin near the articular facets. It is strongly rough with a series of transverse grooves and ridges. The articular facets of the centrum are subcircular and slightly concave. The ventral surface is rounded, without any groove or ridge and strongly concave in lateral view. The neural canal is narrow, but slightly expanded near the articular facets.

Remarks.—The small vertebral centrum (MG 4822) is relatively elongated (length to height ratio is approximately 1.6) and is separated from the neural arch by an open neurocentral suture, suggesting that it belongs to a juvenile individual ( Irmis 2007; Verrière et al. 2022). No evidence of parapophyses or ventral keel is visible in the centrum, indicating that this specimen likely corresponds to a vertebra from the middle or posterior part of the dorsal series. The centrum is spool-shaped, being strongly constricted dorsally by two well-developed pleurocentral depressions lacking pleurocoel. A strong constriction of the centrum is a feature first used to describe Allosaurus fragilis ( Marsh 1877b) . However, similar well-developed pleurocentral depressions are also present in the dorsal vertebrae of several other allosauroids, including Asfaltovenator , Metriacanthosaurus , Sinraptor , Concavenator , and Neovenator ( Currie and Zhao 1993; Brusatte et al. 2008; Carrano et al. 2012; Cuesta et al. 2019; Rauhut and Pol 2019). Moreover, well-developed depressions are also present in some coelurosaurian theropods ( Carpenter et al. 2005). Based on this combination of features and the fragmentary nature of the specimen, we assign this dorsal vertebra to an indeterminate avetheropod.

Figures

Fig. 22. Small dorsal vertebra of a juvenile indeterminate avetheropod (MG 4822) from the Kimmeridgian–Tithonian Sobral Formation, Paimogo (Lourinhã region, Portugal) in?right lateral (A1),?left lateral (A2),?posterior (A3), dorsal (?anterior to the right, A4), ventral (?anterior to the left, A5), and?anterior (A6) views.

Fig.2. Geological and stratigraphical context of fossil sites in the Consolação and Bombarral sub-basins, Portugal. A. Geological map of coastal region of Lourinhã and Peniche with localities yielding fossil remains studied in this work (modified from Camarate França et al. 1960; Manuppella et al. 1999a). B. Map of the Lusitanian Basin with the main structural elements and the different sub-basins (sensu Fürsich et al. 2021). C. Simplified stratigraphy of the Upper Jurassic and Lower Cretaceous sequences in the Torres Vedras and Lourinhã costal region and Consolação-S.Martinho do Porto coastal region based on Hill (1988), Manuppella et al. (1999a) and Azerêdo et al. (2010).Abbreviations:Assen., Assenta; Chron., Chronostratigraphy; Fm., Formation; mb., member; l., lower; m., middle; Oxfor., Oxfordian; sb., sub-basin; u., upper.