Data from: Porosity and water vapor conductance of two Troodon formosus eggs an assessment of incubation strategy in a maniraptoran dinosaur

Using tangential thin sections, we examined variation in porosity and water vapor conductance across two eggs of Troodon formosus, a small (∼50 kg) theropod dinosaur from the North American Upper Cretaceous, testing two hypotheses of egg incubation: (1) full burial within sediments or vegetation and (2) partial burial with exposed upper egg portions. We divided and sampled the eggs in five zones, 1 through 5 from blunt top to more pointed bottom. A geometric model composed of a hemisphere, cone, and paraboloid was used to estimate total and zonal volumes and surface areas. The 138 × 67 mm idealized Troodon egg has a volume, surface area, and mass of 296.4 cm3, 239.23 cm2, and 314.2 g, respectively. Zonal surface areas and volumes highlight the strongly asymmetric and elongate form of the Troodon egg. Geometric modeling provides better estimates of volume and surface area where egg shape diverges markedly from that of a typical bird egg. Porosity varies significantly across both Troodon eggs, with zones 2 and 3 having the largest pores and a majority (70–78%) of total conductance, whereas zone 5 has very low conductance. Total water vapor conductance in the two eggs are 31.85 and 40.62 mg H2O day− Torr−, values 76% and 97% of those predicted for an avian egg of similar size. Low total conductance compares favorably to values in extant birds and non-avian reptiles that incubate in open nests, arguing against full burial incubation. Together with nesting site evidence, low conductance values favor partial burial and incubation by a Troodon adult. Asymmetric egg shape concentrates volume, surface area, and conductance near or at the point of subaerial exposure. Among non-avian dinosaurs, the eggs of Troodon and troodontids are most similar to those of modern birds in having an asymmetric shape, low porosity, no ornamentation, and three structural eggshell layers.

本研究采用切线薄切片技术，对两枚北美上白垩统小型兽脚类恐龙——伤齿龙（Troodon formosus，体重约50 kg）的蛋开展研究，分析其孔隙率与水蒸气传导率的变化，以此验证两种蛋孵化假说：其一为蛋体完全埋藏于沉积物或植被中，其二为蛋体部分埋藏、蛋壳上部暴露在外。
我们将两枚蛋从钝端至尖端划分为1至5共5个区域并进行采样。本研究采用由半球、圆锥与抛物面组成的几何模型，估算蛋体的总体积、区域体积以及总表面积、区域表面积。该理想化伤齿龙蛋尺寸为138×67 mm，其体积、表面积与质量分别为296.4 cm³、239.23 cm²与314.2 g。区域表面积与体积数据凸显了伤齿龙蛋强烈不对称且细长的形态。相较于典型鸟类蛋，当蛋体形态差异显著时，几何模型可提供更为精准的体积与表面积估算结果。
两枚伤齿龙蛋的孔隙率均存在显著区域差异：第2、3区域孔径最大，其水蒸气传导率占总传导率的70%~78%，而第5区域的传导率极低。两枚蛋的总水蒸气传导率分别为31.85与40.62 mg H₂O·d⁻¹·Torr⁻¹，分别为同尺寸鸟类蛋预测值的76%与97%。较低的总传导率与现生鸟类及非鸟类爬行动物开放式巢穴孵化的物种传导率特征相符，这一结果不支持蛋体完全埋藏的孵化假说。结合巢穴遗址证据，低传导率值更倾向于支持伤齿龙成体进行部分埋藏式孵化的假说。
不对称的蛋形使得体积、表面积与传导率集中于或靠近大气暴露的尖端区域。在非鸟类恐龙中，伤齿龙与伤齿龙科的蛋在形态上与现代鸟类蛋最为相似：均具有不对称形态、低孔隙率、无蛋壳纹饰，且具备三层蛋壳结构层。