TAPHONOMY AND PRESERVATION
Complete, articulated specimens of dinosaurs are almost unknown from the Wealden Group of the Isle of Wight, and indeed, are very rare anywhere. Despite this, some dinosaur remains from the Island are extremely well preserved, and, when filled with a variety of diagenetic minerals, such as white calcite and metallic, brassy pyrite, are very beautiful objects. Vertebrate remains in the Wealden Group occur in several distinct states of preservation, depending on the sedimentological facies in which they occur and, to a very large degree, depending on the taphonomic and diagenetic pathways that have led to their preservation. A full scale analysis of vertebrate preservation in the Wealden Group remains to be undertaken, but some preliminary studies, notably those of Clarke (1991), Clarke and Barker (1993) and Clarke et al. (1998) have made inroads into understanding some of the taphonomic histories and diagenetic pathways involved.
Degree of articulation
In general dinosaur skeletons occur as associations of disarticulated
bones where several elements may occasionally approximate the original
articulated condition. Associated bones or partial skeletons are
recorded from the red clays of the Wessex Formation, from some of the
plant debris heds, and occasionally in some of the thinner sandstones.
Near complete, almost three-dimensional skeletons of Hypsilophodon
occur in the so-called Hypsilophodon Bed at the top of the Wessex
Formation where they may represent a mass death assemblage.
Mixed skeletal associations
During excavations of partial skeletons from the plant debris beds, several occurrences have proved to be of multiple individuals of different taxa. Hutt et al. (1996) noted that the partial, disarticulated skeleton of Neovenator salerii was associated with the partial skeleton of an Iguanodon. The partial skeleton of the new theropod Uninasus lengi was associated with remains of Valdosaurus sp. and the ulna of a larger theropod. In both cases the skeletons were dismticulated, but associated, and some of the bones were in very good condition, suggesting that transport was minimal. Teeth were still present in some tooth sockets, although isolated teeth were also found in the surrounding matrix. Insole and Hutt (1994a, b) have suggested that the dinosaurs in the plant debris beds represent the remains of carcasses that drifted into the area following drowning in intrabasinal flood events. This indeed may be the case for some isolated partial skeletons, but drowned carcasses would probably have been fully intact if they had been buried in the flood debris. More likely, the carcasses of the ornithopods were brought in as drowned animals, but the occurrence of the theropods may be attributable to their scavenging on the rotting carcasses of drowned ornithopods and other dinosaurs. A rotting carcass of a large ornithopod such as Iguanodon would prabably be detected by a theropod from several kilometres distant, as theropods are known to have well-developed olfactory lobes of the brain (Brochu 2000). The death of a theropod at the site of a rotting carcass could be attributable to fighting between scavenging theropods, or even due to accidental death caused by the unstable nature of the ground after the flood event (quagmiring or trapped between logs).
Isolated bones
Isolated bones occur frequently in most of the facies of the Wealden Group. In the conglomeratic channel fills of the Wessex Formation isolated bones and teeth are usually broken and may have a polished surface from continued abrasion. Within the plant debris beds and clay facies isolated bones are encountered frequently but, because they are often found in a cliff face or within isolated blocks on the beach, their relationship to other skeletal elements is unknown. Isolated teeth occur in all facies and probably represent shed elements. Isolated teeth of sauropods occur in the Sudmoor Point Sandstone Member between Chilton Chine and Sudmoor Point.
Bone beds
The term bone bed here includes accumulations of bones over and above normal abundance due to agencies of reworking and chemical condensation. It excludes individual skeletons where many bones occur and pertain to one individual. Bone beds are rare within the Wessex Formation but occur frequently as the basal fraction in density sorted gutter casts in the Shepherd's Chine Member of the Vectis Formation. Such guttcr casts are typically between 100 and 500 mm wide and between 30 and 100 mm thick (Plate 1). It is not usually possible to determine their linear extent, although this may be in excess of several metres. Such gutter casts usually have at their base an accumulation of bone material comprising fish teeth (Hybodus and Lepidotes are abundant), opercular bones, isolated vertebrae and other bones with ostracods and rip up clasts of greenish clay. Above the bone rich layer are usually finely laminated cross-bedded, fine sands overlain by finer sands with plant debris. Dinosaur bones are almost never encountered in these beds, but pterosaur remains occur infrequently both as isolated elements and as associated, but disarticulated skeletons (M. Green pers. com).
