Xenoposeidon proneneukos, Taylor & Naish, 2007

D, Michael D. & Emic, 2012, The early evolution of titanosauriform sauropod dinosaurs, Zoological Journal of the Linnean Society 166 (3), pp. 624-671 : 651

XENOPOSEIDON PRONENEUKOS ( TAYLOR & NAISH, 2007)

Xenoposeidon was named on the basis of a single partial middle-posterior dorsal vertebra (NHMUK R2095) from the Early Cretaceous Hastings Beds, UK. Six features were presented as diagnostic for Xenoposeidon by Taylor & Naish (2007: 1549): ‘(1) neural arch covers dorsal surface of centrum, with its posterior margin continuous with that of the cotyle; (2) neural arch slopes anteriorly 35 degrees relative to the vertical; (3) broad, flat area of featureless bone on lateral face of neural arch; (4) accessory infraparapophyseal and postzygapophyseal laminae meeting ventrally to form a V; (5) neural canal is asymmetric: small and circular posteriorly but tall and teardrop-shaped anteriorly; (6) supporting laminae form vaulted arch over anterior neural canal’. Instead of representing autapomorphies, these features are the result of damage or are actually more widespread amongst sauropods. For example, interpreting the flush posterior neural arch-centrum as an autapomorphy (1) does not account for missing bone in the posterior centrum. The forward lean of the neural arch relative to the centrum (2) characterizes dorsal vertebrae of some other sauropods (e.g. Camarasaurus, Osborn & Mook, 1921 : pls 69, 72). Likewise, the laminar pattern characters (3, 4, 6) are observed in a variety of sauropods when individual or serial variation are explored (e.g. Camarasaurus, Osborn & Mook, 1921 ; Brachiosaurus, Riggs, 1903 ; Tehuelchesaurus, Carballido et al., 2011b . The ‘asymmetrical neural canal’ (5) cited by Taylor & Naish (2007) misrepresents the large centroprezygapophyseal fossae as the entire anterior neural canal, which is a feature observed in many neosauropods (e.g. Camarasaurus, Osborn & Mook, 1921 ). The absence of diagnostic features renders Xenoposeidon a nomen dubium (as also suggested by Mannion & Calvo, 2011). The presence of coarse camellate pneumaticity suggests that NHMUK R2095 pertains to a titanosauriform.