Heat transfer in a realistic clutch reveals a lower efficiency in incubation of oviraptorid dinosaurs than of modern birds

Chun-Yu Su^1,2Jun-Yang Liao^3,4Hsiao-Jou Wu⁵Kuan-Yu Chou⁵Ching Chen⁵Ming-Tsang Lee^6*Tzu-Ruei Yang^5,7,8*

• ¹Washington High School, Taiping, Taichung County, Taiwan
• ²Harvard University, Cambridge, Massachusetts, United States
• ³Inventec Corporation, Taipei, Taiwan
• ⁴Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu City, Hsinchu County, Taiwan
• ⁵Department of Geology, National Museum of Natural Science, Taichung, Taiwan
• ⁶Department of Power Mechanical Engineering, Tsing Hua College, National Tsing Hua University, Hsinchu, Hsinchu County, Taiwan
• ⁷Department of Earth Sciences, National Cheng Kung University, Tainan, Tainan County, Taiwan
• ⁸Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan

It has been proposed that some reproductive traits specific to birds, such as thermoregulatory contact incubation (TCI), may also have been present in oviraptorosaurians, as inferred from clutch-associated oviraptorid adults with postures resembling avian brooding behavior. Nevertheless, prerequisites for TCI, such as the incubating adult providing the majority of heat needed for normal embryonic development, have only been quantitatively evaluated once. To test this, a realistic Heyuannia huangi incubator, oviraptorid clutches, and heat transfer numerical simulations were developed to simulate the brooding behavior of Heyuannia huangi and Nemegtomaia barsboldi. Our results indicate that the incubator could only partially contact the outer-ring eggs of the clutch, leading to a temperature difference between the inner and outer rings and a lower incubation efficiency compared to that of extant birds. Additionally, an outer-ring egg had a considerably higher temperature than the superimposed inner-ring egg when positioned near the incubator's core, whereas an outer-ring egg had approximately the same temperature as the superimposed inner-ring egg when positioned closer to the incubator's periphery. If Nemegtomaia barsboldi were to initiate incubation before clutch completion, the temperature distribution could cause the outer-ring egg at the incubator's core to hatch earlier than the inner-ring egg immediately beneath it, whereas at the periphery the inner-ring egg could hatch earlier than the outer-ring egg immediately above it. However, irrespective of position, the inner-ring egg of Heyuannia huangi may hatch earlier than the outer-ring egg immediately above it. Our findings do not support the TCI hypothesis and suggest that the adult's brooding posture may influence the pattern of asynchronous hatching.