JURASSIC DINOSAURS AND INSECTS: THE PALEOECOLOGICAL ROLE OF TERMITES AS CARRION FEEDERS

As plant decomposers, termites (Isoptera) are renowned for their ability to return nutrients to the environment. Termites also consume bone from vertebrate carcasses, possibly for colony-limiting nutrients. Such behavior, however, is poorly known and understood. New fossils and reinterpretations of trace fossils on bone from the Upper Jurassic Morrison Formation of the western U.S. and Middle Jurassic Shishugon Formation of China show that termites played a major ecological role as decomposers of Earth's largest terrestrial vertebrates – the dinosaurs.

Dinosaur bone from the Morrison Formation often exhibits trace fossils consisting of circular shallow pits 0.5-20mm wide and <5mm deep. Pits occur in small groups (random, rings, or lineations), massive clusters, and in some cases envelop bones, amounting to bone loss on the sub-cm scale. In a sample of 21 Morrison quarries, 15 have pitted bones. In one quarry, over 47% of the sampled bones (n=306) are pitted. Pits frequently occur on a single surface but may cover all non-articular surfaces. They are most common on limb, ventral pelvic, and elongate bones such as ribs and metapodials, but show no affinity to specific vertebrate taxa.

Such pits were previously interpreted as dermestid beetle (Coleoptera) pupal chambers. The pits, however, are shallow circular depressions and occur in a range of sizes, whereas dermestid pupal chambers are flask-shaped, with a narrow neck and deep chamber, and are of a fixed size depending on species. Foraging traces made by extant termites on bone are similar in morphology, size, and pattern to the pits on Jurassic bone, indicating termites, not beetles, are responsible the pits on dinosaur bones. Extant termites usually attack bones in the dry season after a carcass is dry and devoid of soft tissues. Recently discovered foraging galleries covering pitted areas of dinosaur bones are further evidence for the termite hypothesis and against the dermestid hypothesis, because dermestids do not create galleries. Studies of extant termites on carcasses involved only subaerially exposed bones but preservation of foraging galleries on the dinosaur skeleton indicate bones can be infested post burial and thus the taphonomy of some Jurassic sites will require reinterpretation.