Nesting and Egg Incubation in Dinosaurs: Morphological and Statistical Investigations into the Study of Eggs, Eggshells, and Nests
Abstract
Archosaurs (e.g., crocodylians, dinosaurs, and birds) are the most diverse and successful terrestrial vertebrates. An understanding of the nesting strategies in both extinct (e.g., non-avian dinosaurs) and extant archosaurs (i.e., crocodylians and birds) is crucial for advancement of our knowledge on the evolution and diversification of this group. However, nesting methods and behaviors of non-avian dinosaurs are still poorly understood due to the limitations of the fossil record. In this dissertation, certain features of eggs and nests in dinosaurs (e.g., clutch size, egg mass, substrates of nests, water vapor conductance of eggs, and eggshell porosity) are compared with those of their closest living relatives (i.e., birds and crocodylians) and aspects of dinosaur nesting (i.e., nest type, incubation behavior, incubation heat source, and incubation period) are inferred and reconstructed.
Findings in this dissertation suggest that nests and nesting styles among non-avian dinosaurs were diverse, and that bird-like traits were acquired throughout their evolution. Analyses of eggs and eggshell porosity indicate that more basal dinosaurs (i.e., ornithischians, sauropodomorphs, Lourinhanosaurus) completely covered their eggs with nest materials during incubation, although more derived forms (e.g., oviraptorosaurs, troodontids) used open nests, like modern birds, in which the eggs were not fully buried. The lithologies of the clutches of basal dinosaurs reveal their nests were probably incubated with external heat sources (e.g., microbial respiration, solar radiation), like those of modern crocodylians and megapode birds. Distribution and lithologies of some ornithischian and some sauropodomorph clutches show that heat from microbial respiration, in particular, was used for incubation, whereas other sauropodomorphs may have used inorganic heat sources, such as solar radiation. More derived dinosaurs (i.e., maniraptorans) had eggshell porosities and clutch lithologies that indicate their nests were partially open, indicating that these taxa brooded their eggs. Regardless of the type of nest, heat source, or incubation behavior, incubation period of most non-avian dinosaurs examined was relatively short, more comparable to that of birds than crocodylians. Major dinosaur (and archosaur) clades show diversity in their nesting and incubation, and also reveal a transition to more bird-like nesting features through evolution.
Description
Keywords
Paleontology
Citation
Tanaka, K. (2016). Nesting and Egg Incubation in Dinosaurs: Morphological and Statistical Investigations into the Study of Eggs, Eggshells, and Nests (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27073