USING BURIAL EXPERIMENTS TO UNSCRAMBLE DINOSAUR EGG TAPHONOMY

Through an unlikely set of circumstances, Colgate University came to possess one of the first whole dinosaur eggs ever discovered. Our 80 million-year-old oviraptorid specimen is from the first clutch of dinosaur eggs found during the 1923 expedition to the Gobi Desert of Mongolia led by Roy Chapman Andrews. Taphonomic experiments were designed as part of a pilot study to document (a) the chronological stages in the decay, fracturing, disintegration, transport, and removal of eggs exposed at the surface and buried in sand; (b) the effect of biological and non-biological agents on the rates and patterns of decay; and (c) directions for future research to develop and test hypotheses about the preservation of Oviraptor eggs in Mongolia.

Experiments involving burial of four egg types and more than 100 eggs were conducted in the lab and at two field sites over a three-month period. Post-exhumation analysis revealed that the preliminary stages in the fossilization of eggs include rapid fracturing, weight change, sand casting, limited decay, and significant egg loss through scavenging. These results suggest that the eggshell’s tendency to fracture, its architectural strength to withstand collapse, infill by sediment, and internal membranes together elevate fossilization potential. Significantly, holes and depressed fractures on the dorsal side of some buried specimens produced a feature that is similar to "hatching windows," described as evidence that juveniles had emerged from eggs at dinosaur nesting sites. Recent examination of Cretaceous eggs from the Aix-en-Provence basin in France confirms that the gaping holes interpreted to be "hatching windows" resemble those in our experimental eggs. In our study, however, these features formed in infertile eggs as a result of scavengers or brittle fracture, contents seepage, and collapse. Thus similar broken eggs or collapsed eggshell features should be interpreted with caution from fossil egg sites.

Despite the extraordinary paleontological significance of dinosaur eggs, their taphonomy is poorly understood. Ongoing experiments will ensure that egg taphonomy is better understood so that informed interpretations can be made about fossil eggs, preservational conditions, and dinosaur reproductive ecology.