INSECT TRACE FOSSILS ON DINOSAUR BONES FROM THE UPPER JURASSIC MORRISON FORMATION OF NORTHEASTERN WYOMING

Forensic entomology, commonly used in criminal investigations, is the study of necrophagous arthropods on carcasses to determine the amount of time lapsed since the death of the organism. A carcass with flesh clinging to the bones must be exposed for an extended period of time to attract insects. Most of these insects feed exclusively on soft tissues, while very few modify bone. The larvae of dermestid beetles feed on desiccated carcasses and etch feeding traces and bore pupation chambers into the bone surface. The size, shape, and type of trace vary with temperature, light, food availability, moisture level inside the carcass, and amount of time the carcass was exposed after death. Three distinct types of insect traces are found on dinosaur bones from the Upper Jurassic Morrison Formation of northeastern Wyoming. Concepts of forensic entomology are used to determine which insects created the traces on the bones, and how long the dinosaurs were exposed prior to burial. The first trace is a narrow, looping groove etched into the bone surface. This trace is interpreted as a feeding trail of an unknown insect. The most common trace on the dinosaur bones is from an unidentified insect. This trace is a shallow, spherical pit, interpreted as a pupation chamber. The third trace, interpreted as a dermestid beetle pupation chamber, is a deep, flask-shaped boring that varies in diameter and density between individual skeletons. The absence of insect traces on a skeleton suggests that the carcass was rapidly buried, submerged in water, or was exposed to a moist climate that prevented desiccation. Skeletons with larger dermestid borings likely had more available flesh and a prolonged exposure of the carcass during favorable environmental conditions compared to skeletons where the borings are small or absent. Skeletons with the longest subaerial exposure are expected to have the highest number and diversity of insect traces.