FOWLER, D.W., SIMMONDS, K., GREEN, M., & STEVENS, K.A. (2003), The taphonomic setting of two mired sauropods (Wessex Fm, Isle of Wight, UK), palaeoecological implications and taxon preservation bias in a Lower Cretaceous wetland, Journal of Vertebrate Palaeontology 23(3, supp): 51A

ABSTRACT

The Wessex Fm. (Barremian, Lower Cretaceous) of the Isle of Wight, UK, has historically yielded many tantalising fragments of sauropod dinosaurs. Here we describe the taphonomic setting of a new site preserving two small conspecific individuals, possibly diplodocid, and discuss the palaeoecological implications.

Three small forelimbs (1.2 m in length) are preserved articulated in life position with both individuals facing south, 4 m apart, in the same horizon. The vertical attitude of the bones, a lack of elements other than the limbs, and their preservation in smectite rich palaeovertisols (mottled/red marls) strongly suggests a miring event. A shed theropod tooth found with the bones supports the likely hypothesis that the mired carcasses were subsequently scavenged, leaving only the embedded limbs to be preserved. The coincidental miring of two possibly juvenile conspecific sauropod dinosaurs raises many intriguing palaeoecological questions. Other unpublished sauropod sites within the Wessex formation similarly demonstrate taphonomic conditions suggestive of miring events.

Tentative evidence supports the hypothesis of taxon preservation bias between different facies. Sauropod remains, many recognisably in situ, constitute a higher percentage of the megafauna within red and purple marls (medium to well drained oxidised sediment) than other facies. The most productive facies, plant debris beds (waterlogged reduced sediment, formed by fire-flood associations), yield an allocthonous megafauna dominated by the large ornithopod dinosaur Iguanodon. The Hypsilophodon bed (mottled sand/mud facies, mudflows) yields a megafauna almost exclusively composed of small subadult/juvenile Hypsilophodon very commonly preserved articulated in 3 dimensions. These morphologically dissimilar taxa were likely susceptible to different preservation biases, manifested in the fossil record by their preferential preservation in different facies.