An anterior sauropod caudal from the Peterborough Oxford Clay: Whose tail is it anyway?

The Callovian Oxford Clay of England has yielded a rich and diverse marine fauna, mainly discovered and described by Alfred Leeds. However, occasionally it also brought forth terrestrial fossils, including four isolated cases of sauropod remains, one of a stegosaurid, and another of a dryosaurid. Thus far, only Cetiosaurus oxoniensis and Cetiosauriscus stewarti are confirmed sauropod taxa from these beds. Here, we describe an isolated sauropod anterior caudal vertebra from the Oxford Clay near Peterborough. Incomplete, it has been immersed in seawater post-mortem, indicated by the adhesion of molluscs, but some characters can nevertheless be used for diagnosis and comparisons. The anterior articular surface is round, whereas the posterior articular surface is heart- shaped, as in many eusauropods, including Cetiosaurus. Interestingly, the ventral surface shows a keel-like structure; a character shared with neosauropods (e.g. Barosaurus) but also with an as yet unnamed Middle Jurassic sauropod caudal from York, UK. The posterior side of the neural canal is teardrop-shaped, a character shared with most basal eusauropods. Below the posterior neural canal, a lip-like structure seems to be present; a character which is shared with Cetiosaurus. However, the anterior caudal transverse process (ACTP) complex is similar to, although more pronounced than Cetiosauriscus, being more similar to more derived sauropods (Neosauropoda). Thus, an incomplete isolated element may help elucidate sauropod species diversity and dispersal in the Middle Jurassic of England.