INSECT TRACES ON THE SURFACE OF DINOSAUR BONES FROM THE CARNEGIE QUARRY (CQ) IN THE UPPER JURASSIC MORRISON FORMATION AT DINOSAUR NATIONAL MONUMENT (DINO), JENSEN, UT

The Quarry Exhibit Hall at DINO houses a spectacular wall of >1,600 in-situ dinosaur bones. The quarry consists of a fluvial sandstone deposit within the Brushy Basin Member of the Morrison Formation and includes Diplodocus, Camarasaurus, Stegosaurus, Apatosaurus, Allosaurus, Camptosaurus, Barosaurus, Dryosaurus, crocodilians, and turtles. The taphonomy of CQ has been described previously, including a preliminary survey of insect traces on bone surfaces. Traces consist of small (0.5–5 mm diameter), shallow (1–2 mm deep), circular pits and sinuous furrows made by osteophagous insects boring into the bone surface prior to burial. This study was conducted as part of the AmeriCorps Geoscientists-In-the-Parks program, with the objective of: 1) investigating the diversity, abundance, and distribution of insect traces on CQ bones and 2) augmenting visitor experience by providing casts of the insect traces for the rangers to share with visitors.

Study of 1468 bones from the quarry face revealed 181 (12%) with insect traces. The taxon, element, presence/absence of insect traces, surrounding lithology, and trace morphology, location, dimensions, and density were noted. Four trace types were identified: 1) large borings (circular, 2–5 mm), 2) small borings (circular, 0.5–1.99 mm), 3) rosettes (ring-shaped circular bores), and 4) furrows (sinuous troughs). Representative examples of each of the four trace types were molded using Alumilite silicone mold putty and cast with Alumilite RC-3 plastic resin. Barosaurus and Apatosaurus had the highest percentage of insect surface modification (28% and 21%, respectively) and the scapula/coracoid and pelvic elements had the highest percent of insect surface modification (36% and 23%, respectively).

Extant osteophagous insects include dermestid beetles (Coleoptera: Dermestidae) and termites (Isoptera: Termitidae). Rosettes are characteristic traces made by termites on modern-day bone and suggest that this group is responsible for most of the insect traces in the CQ. Both groups play a major role in the decomposition process and leave distinctive marks on bone surfaces similar to those observed in the CQ and other dinosaur bonebeds. These traces indicate that osteophagous insects were a significant agent of vertebrate decomposition during the Jurassic.