THE TRACES OF INSECTS AND MAMMALS FOUND ON DINOSAUR SKELETONS FROM UPPER CRETACEOUS EOLIAN DEPOSITS IN MONGOLIA

We describe herein the formation processes of trace fossils—including shallow to deep pits, notches, borings (tunnels), and channels, particularly at the limb joints— observed on the surfaces of dinosaur skeletons from Upper Cretaceous eolian deposits in the Gobi Desert, Mongolia. Eolian deposits are widely distributed throughout Upper Cretaceous dinosaur localities in the Gobi Desert. The Djadokhta (Middle Campanian) and Barun Goyot (Middle - Late Campanian) Formations in particular include a number of eolian deposits. In the present study, we investigated trace fossils on the surfaces of an articulated Protoceratops (HMNS 94-10-11) skeleton from the Djadokhta Formation in Tugrikin-Shireh, located in the central part of the Gobi Desert, and an articulated Bagaceratops skeleton (HMNS 94-03-05) from the Barun Goyot Formation in Khermeen Tsav, located in the southwestern part of the Gobi Desert. The median diameters of these structures range from 6.3 to 8.0 mm, similar in size to those found in ankylosaurid specimen (HMNS 98-16-13) from the same locality as Protoceratops. We concluded that these structures were created by insects scavenging on and pupating in dinosaur carcasses. This interpretation was confirmed by the discovery of similar-sized sand pipes and natural casts of pupal cocoons at the same locality. Broad borings (about 32 mm in diameter) created by small Mesozoic mammals have also been discovered on the ribs and scapulae of Protoceratops skeleton. Dinosaur remains found at two sites, Tugrikin-Shireh and Khermeen Tsav (Middle to Late Campanian), exhibited the same type of damage to the limb joints. The high frequency of trace fossils at the limb joints suggests that small animals targeted the collagen in the joint cartilage of dried dinosaur carcasses as a source of nitrogen, which was relatively scarce in the eolian environments of the Gobi desert during the Late Cretaceous.