The egg-thief architect: experimental oviraptorosaur nesting physiology, the possibility of adult-mediated incubation, and the feasibility of indirect contact incubation

Abstract

Numerous, high-quality reproduction-related oviraptorosaur fossils have been described. However, oviraptorosaur-style nests are unknown among extant animals, and their curious construction makes nesting behavior difficult to interpret. Experiments were undertaken to better understand oviraptorosaur nesting strategies. A surrogate was constructed and placed atop mock-oviraptorosaur nests built from sand and 36 infertile emu eggs (as Macroolithus approximations) arranged according to the most current nest reconstructions. Thermometers, placed within each egg and throughout the experimental area, recorded energy flow from the surrogate dinosaur into the nesting microenvironment. One experiment examined a basic open nest warmed from above; the second, a fully buried clutch warmed from above; and the third, a nest open like the first but with heating elements (representing hindlimbs) extending down into the nest. It was found that egg temperatures in each scenario surpassed ambient temperatures without requiring excessive energy input. Final clutch temperatures were below most avian values, closer to crocodilian incubation, but are likely conservative, considering experimental parameters. These results may support the idea that an oviraptorosaur could use adult-generated energy to warm a clutch above ambient conditions. Additionally, egg tiers would be warmer and more uniform in temperature if heated by elements within the nest, such as hindlimbs, instead of solely from above. Results from the second experiment indicate that an endothermic adult could possibly warm a clutch fully buried beneath itself despite a barrier. Although not likely a behavior exhibited by oviraptorosaurs, such results suggest an important evolutionary step bridging guarded subterranean eggs and contact-incubated subaerial eggs.