NOVEL OCCURRENCES OF ICHNOTAXA CREATED BY INSECTS ON DINOSAUR BONES FROM THE GRAY ASH QUARRY (YELLOW CAT MEMBER OF THE CEDAR MOUNTAIN FORMATION, EARLY CRETACEOUS) OF EASTERN UTAH

The Cedar Mountain Formation in Utah, USA has become a hotspot of dinosaur discovery. Fossils of sauropods, theropods, ankylosaurs, and ornithopods recovered from the formation provide insight to the ecosystem and biodiversity of western North America during the Early Cretaceous.

Here we report the discovery of substantial trace fossils created by the feeding and foraging activity of insects on dinosaur bones. These bones were recovered from the Gray Ash Quarry in the 125 Ma Yellow Cat Member of the Cedar Mountain Formation. This member consists of silty mudstones to fine-grained sandstones, representing fluvial and related overbank deposits.

The Gray Ash Quarry represents a splay deposit in the Yellow Cat Member and preserves disarticulated, trampled, and scavenged dinosaur bones in a diamictite composed of a green, silty mudstone matrix and red chert clasts. Vertebrate fossils consist of sauropod bones and large theropod teeth. Some bones exhibit only isolated traces, while others are almost completely destroyed by insect activity. Over 70% of the bones from the quarry exhibit traces.

The traces consist of pits, holes, furrows, channels, and borings, and mandible marks. Frass (feces consisting of minute bone fragments), created as the trace maker consumed the bone, is found in the matrix surrounding the bones and in some traces. Grooves are present in many traces and are interpreted as mandible marks. Burrows of variable fill, usually clay or frass, have also been discovered. Some burrows are contiguous with traces in the bone.

Channels and furrows are assigned to Osteocallis sp. Burrows contiguous with channels are assigned to Amphifaoichnus seilacheri. Pits, holes, and borings are assigned to Karethraichnus lakkos and cf. Cubiculum.

While trace fossils created by insects on dinosaur bones have been reported from the Cedar Mountain Formation before, this study is the first to examine these traces in detail and assign ichnotaxa. Determining the ichnotaxa present in this quarry sheds further light on trophic interactions and the ecosystem of the Cedar Mountain Formation.