TAPHONOMY OF THE MAY RAE DINOSAUR QUARRY, UTAH (YELLOW CAT MEMBER OF THE CEDAR MOUNTAIN FORMATION, EARLY CRETACEOUS, BARREMIAN)

The Yellow Cat Member of the Cedar Mountain Formation has yielded the Western Hemisphere's most abundant terrestrial vertebrate fauna. A relatively new site, May Rae, in this stratum continues that trend. The site is dominated by Gastonia (MNI=6), a nodosaurid, with scanty remains of Cedarosaurus & Moabosaurus (Sauropoda), Utahraptor, and a large unidentified taxon (Theropoda). Unionid bivalves are also present. Vascular plants are represented by root casts.

The bone horizon occurs at the base of a 4-m-thick unit of laterally thin-bedded siltstones and mudstones, some of which are overprinted with thin paleosols. This horizon is interpreted as a stack of splay deposits. The bone-bearing silty mudstone horizons vary from 0 to 0.5 m thick and are interpreted to represent multiple splay events. Root casts are common in the bone horizons, but the widely spaced and shallow casts suggest they represent a single growing season, that is an inceptisol.

Bone pebbles are common and indicate small bones or bone fragments had traveled some distance before final deposition. In contrast, articulated and closely associated skeletal elements show that some bones were minimally transported or were enveloped in soft tissues during fluvial transport. While there are rare examples of articulation and close association of bones, most are fully disarticulated. Excluding dermal armor, most bones are broken, often obliquely, and this, along with subparallel scratch marks on smooth bones indicates the bones were trampled. The oblique fractures indicate the bones were trampled while green. Insect burrows and mandible marks are uncommon. Most bones show no evidence of pre-depositional weathering, indicating they had not been sitting in direct sun and heat for an extended period.

Tooth marks are present on some Gastonia spikes, scutes, and an ilium. They are characterized by recognizable shallow pits bordered by pressure-formed ridges. These are interpreted as crocodilian feeding traces.

In sum, the MayRae site is interpreted as a series of splay deposits that preserve bones of dinosaurs that had been bitten, trampled, and buried in sediments that were briefly rooted before subsequent burial by subsequent splays (flooding events).