Using Burial Experiments to Unscramble the Taphonomy of Colgate's Dinosaur Egg
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 (click here for more details
). Its importance cannot be overemphasized because the egg (and its sibling eggs) provided the first definitive evidence of how some dinosaurs reproduced, opening up a whole new area of research on dinosaurs.
Since Andrews' discoveries in the Gobi, dinosaur eggs have been found on every continent, except Antarctica, but scientists still know very little about what it takes to fossilize an egg. At Colgate, David Goldsmith ('93) determined on the basis of x-rays and CAT scans that our dino egg contains no embryo.
Subsequent taphonomic (burial) experiments were designed with Colgate geology students as part of a pilot study to determine the processes responsible for egg preservation in the geologic record.
In our pilot study, experiments involving four egg types and more than 100 eggs were conducted in the lab and at two field sites over several months by David Sunderlin ('99) and Steve Close ('99). Their goal was 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.
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. My recent examination of Cretaceous dinosaur 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, content seepage, and collapse. Our working hypothesis is that the so-called "hatching windows" in the French dinosaur eggs formed through putrefaction and decay, rather than from the activities of hatchlings. Similar broken eggs or collapsed eggshell features should be interpreted with caution from fossil egg sites.
In the summer of '04, funds from NSF, Colgate's Council for Faculty Development, and the geology department's Boyce Fund made it possible to visit Bayan Zag ("Flaming Cliffs") in the Gobi Desert where Colgate's dinosaur egg was discovered in 1923. It's an absolutely amazing place -- red sandstones form an impressive but easily negotiated escarpment sculpted into stunning buttes and pillars. The rocks forming Bayan Zag are remarkable in many ways: thick, massive, and structureless, they provide few discernible clues about their origin. Preserved traces of ancient plants and animals in the form of delicate and intricate burrows indicate a sand dune environment where lots of activity was taking place below the surface.
I did a solo hike from our desert campsite to the top of Bayan Zag at dawn. What an adventure to be there as the sun was coming up, encouraging the rocks to take on that legendary red blush. Knowing our egg's historical significance, not just to Colgate but to paleontology, added an emotional element to walking in Roy Chapman Andrews' footsteps that particular morning. I may be the first Colgate person to go to the site where our egg was found since its discovery more than 80 years ago.
Despite the extraordinary paleontological significance of dinosaur eggs, the factors that favored their burial and fossilization (taphonomy) are largely unknown. Ongoing experiments at Colgate will ensure that egg taphonomy is better understood. This will allow more informed interpretations to be made about fossil eggs, preservational conditions, and dinosaur reproductive ecology.