INSECT TRACE FOSSILS ON DINOSAUR BONES FROM THE UPPER JURASSIC MORRISON FORMATION, NORTHEASTERN WYOMING, AND THEIR USE IN VERTEBRATE TAPHONOMY

The skeletons of a diplodocid and three Camarasaurus sauropods, ranging from mostly articulated to disarticulated, were collected from a quarry in the Upper Jurassic Morrison Formation in northeastern Wyoming by the University of Kansas during the 1997, 1998, 2002, and 2004 field seasons. Preparation revealed five types of trace fossils on the bone surfaces--shallow pits; rosettes; hemispherical pits; thin, curvilinear grooves; and U- to V-shaped grooves. These traces were identified through comparison with traces produced on bone and wood by modern organisms. The shallow pits, rosettes, and hemispherical pits are interpreted as pupation chambers constructed by dermestid beetles, or another holometabolous insect with a similar behavior. The morphology of these traces is distinct from traces produced by such other bone-modifying insects as termites and tineid moths. The thin, curvilinear grooves and are interpreted as rhizoetchings that were chemically etched into the bones after burial. The U- to V- shaped grooves are likely bite marks produced by a large theropod or crocodilian while feeding on the sauropod carcasses. Application of the concepts of forensic entomology and the study of the disarticulation and scattering of vertebrate carcasses after death are used to understand better the taphonomy of the sauropods at the quarry. Necrophagous insects that bore into bone, such as dermestid beetles, only feed on desiccated carcasses that are subaerially exposed. The sauropods likely died during the dry season, which allowed time for their carcasses to desiccate (~3 weeks) and for the insects to arrive and lay eggs, hatch into necrophagous larvae, feed on the carcasses, and pupate (~4 weeks). Overlapping traces provide evidence that at least two generations of bone modifying insects fed on the carcass of one large Camarasaurus. The diplodocid died first--its remains were scattered and subaerially exposed approximately 1-3 years before the other sauropods died at the locality. The large Camarasaurus died second and was exposed and fed upon by the first generation of bone-modifying insects. Approximately five weeks after its death, the final two Camarasaurus died at the locality and were infested by bone-modifying insects. A second generation of insects colonized the large Camarasaurus carcass and all four sauropod carcasses were shallowly buried during a flooding event. Two new ichnogenera and three ichnospecies are erected for the shallow pits; rosettes, and hemispherical pits on the sauropod bones. Osteogronos contains two ichnospecies: the shallow pits are named O. hyposkytos and the rosettes are named O. nyssa. Both ichnospecies are restricted to the Upper Jurassic Morrison Formation in Wyoming and Utah. Osteokryptos entaphiopoles is named for the hemispherical pits. Hemispherical pits found on Neogene bones from Africa and North America were originally referred to Cubiculum ornatus, however, the morphology of these traces are identical to O. entaphiopoles and they are transferred to this ichnospecies. [The ichnotaxonomic paper that defines these new ichnotaxa is currently under review; therefore, the names used here are unofficial and are used here informally]