Open Paleo

Xenoposeidon

Taylor & Naish, 2007 ZEE-no-puh-SYE-don

From Greek xenos meaning 'strange' or 'alien' and Poseidon (the Greek god of the sea), in allusion to the sauropod genus Sauroposeidon; translates as 'strange Poseidon'

143.1–137.1 million years ago Berriasian, Early Cretaceous
Early Cretaceous stages

Xenoposeidon is a genus of rebbachisaurid sauropod dinosaur from the Early Cretaceous of England, living about 140 million years ago. It is known from a single partial vertebra with unusual features, unlike those of other sauropods. This bone was first discovered in the early 1890s but received little attention until it was found by University of Portsmouth student Mike Taylor, who formally described and named it in 2007 with Darren Naish.

Under dispute

Originally described as a neosauropod of uncertain affinity (Taylor and Naish, 2007). D'Emic (2012) judged its distinguishing features to be damage or widespread among sauropods, regarded it as a nomen dubium, and took its camellate pneumaticity to indicate a titanosauriform. Taylor (2018) rebutted this point by point, rediagnosed it on five characters, and reinterpreted it as the earliest known rebbachisaurid on the basis of a shared neural-arch lamina arrangement, a placement resting on morphological argument rather than a numerical analysis.

Diagnosis

  1. Neural arch covers dorsal surface of centrum, with posterior margin continuous with 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

Species

Xenoposeidon proneneukos Taylor & Naish, 2007

Type species

From Ancient Greek meaning 'forward sloping', describing the distinctive anterior lean of the neural arch, the most conspicuous anatomical feature of the holotype vertebra.

Holotype
BMNH R2095 , Natural History Museum
Material
A mid posterior dorsal vertebra consisting of partial centrum and neural arch.
Horizon
Ashdown Formation, Berriasian, Early Cretaceous , 143.1–137.1 million years ago
Locality
Ecclesbourne Glen, East Sussex, United Kingdom Taylor and Naish (2007) give the locality as "probably Ecclesbourne Glen", the "Precise locality and stratigraphic information" having been lost or never recorded, and the horizon as the "probably Berriasian part of the Ashdown Beds Formation", since the part exposed there is Berriasian. Taylor (2018) likewise puts it at around 140 million years, Berriasian on the ICS chart v2024/12.

References

  1. Taylor, M. P.; Naish, D. (2007). An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50(6): 1547-1564. Wiley. doi:10.1111/j.1475-4983.2007.00728.x taylor2007a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the hip height estimate.

    jones2026b
  3. Taylor, M. P. (2018). Xenoposeidon is the earliest known rebbachisaurid sauropod dinosaur. PeerJ 6: e5212. doi:10.7717/peerj.5212

    Reinterpreted Xenoposeidon as the earliest known rebbachisaurid based on shared vertebral lamina arrangement with Rebbachisaurus

    taylor2018a
  4. D'Emic, M. D. (2012). The early evolution of titanosauriform sauropod dinosaurs. Zoological Journal of the Linnean Society 166: 624-671. doi:10.1111/j.1096-3642.2012.00853.x

    Regards Xenoposeidon as a nomen dubium and suggests from its camellate pneumaticity that it is a titanosauriform.

    d'emic2012b