INVERTEBRATE BURROWS ON DINOSAUR BONES FROM THE LOWER CRETACEOUS CEDAR MOUNTAIN FORMATION NEAR MOAB, UTAH, U.S.A

Burrowed bones from the Dalton Wells Quarry (DWQ) near Moab, Utah provide evidence for the trophic relationship between osteophagous invertebrates and six of the nine dinosaurian genera known from the locality. Burrows are present on 12% of the prepared bones (n=3061). The bonebed is preserved in clayey siltstones of fluvial (debris flow) origin deposited in a marginal lacustrine environment. Sedimentological evidence indicates the bones were deposited and buried in a saturated substrate. Bone-burrow-matrix relationships indicate the burrows were constructed after deposition. The burrows are surficial (50% of the burrow in bone, 50% in matrix) and sinuous with a width of 0.5-18mm. Size range may reflect the ontogeny of a single invertebrate species (larva to adult) or the necrophagous behavior of several species of varying size and mandibular strength. Burrows up to 400mm long occur on elongate bones but most are short swaths on articular surfaces. Some burrows form galleries with lateral chambers. Burrow fillings contains fine bone fragments indicating bone was a source of nutrients. Paired grooves <11mm long are interpreted as mandible marks. Pairs of mandible marks occur at many angles within a single burrow indicating extensive head mobility. Coleopterans (beetles) are known to have strongly sclerified mandibulae capable of impacting bone and we tentatively conclude the burrower is a strong-jawed beetle larva of substantial size. Possible candidates are beetles of the Silphidae or Histeridae but non-coleopteran larvae cannot be ruled out. Previously reported pits and burrows on bone from the Jurassic and Cretaceous have been attributed to dermestid beetle larvae, a group that feeds in drier, subaerial conditions. Sedimentology and burrow morphology at DWQ indicate dermestids are unlikely candidates.