Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs

Abstract

Knowledge about the types of nests built by dinosaurs can provide insight into the evolution of nesting and reproductive behaviors among archosaurs. However, the low preservation potential of their nesting materials and nesting structures means that most information can only be gleaned indirectly through comparison with extant archosaurs. Two general nest types are recognized among living archosaurs: 1) covered nests, in which eggs are incubated while fully covered by nesting material (as in crocodylians and megapodes), and 2) open nests, in which eggs are exposed in the nest and brooded (as in most birds). Previously, dinosaur nest types had been inferred by estimating the water vapor conductance (i.e., diffusive capacity) of their eggs, based on the premise that high conductance corresponds to covered nests and low conductance to open nests. However, a lack of statistical rigor and inconsistencies in this method render its application problematic and its validity questionable. As an alternative we propose a statistically rigorous approach to infer nest type based on large datasets of eggshell porosity and egg mass compiled for over 120 extant archosaur species and 29 archosaur extinct taxa/ootaxa. The presence of a strong correlation between eggshell porosity and nest type among extant archosaurs indicates that eggshell porosity can be used as a proxy for nest type, and thus discriminant analyses can help predict nest type in extinct taxa. Our results suggest that: 1) covered nests are likely the primitive condition for dinosaurs (and probably archosaurs), and 2) open nests first evolved among non-avian theropods more derived than Lourinhanosaurus and were likely widespread in non-avian maniraptorans, well before the appearance of birds. Although taphonomic evidence suggests that basal open nesters (i.e., oviraptorosaurs and troodontids) were potentially the first dinosaurs to brood their clutches, they still partially buried their eggs in sediment. Open nests with fully exposed eggs only became widespread among Euornithes. A potential co-evolution of open nests and brooding behavior among maniraptorans may have freed theropods from the ground-based restrictions inherent to covered nests and allowed the exploitation of alternate nesting locations. These changes in nesting styles and behaviors thus may have played a role in the evolutionary success of maniraptorans (including birds).

Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development

“…Speculation that neonates of large ornithischian dinosaurs (e.g., ceratopsians and hadrosaurids) made 2,600-to 3,200-km migrations from lower latitude nesting grounds to rich summer feeding grounds in the Arctic may have been infeasible because of unexpectedly short posthatching windows for seasonal travel (75)(76)(77). Finally, hypotheses regarding nest microenvironment (43, 61), eggshell gas conductance (61,78,79), embryonic physiology (45), reproductive effort, annual numbers of clutches and taxon generation times (21,80,81), and developmental mode (43) can be strengthened or formally tested in light of slower in ovo dinosaur development. These results may have implications for nonavian dinosaur extinction.…”

Collection of the thinnest: A unique eggshell assemblage from the Late Cretaceous vertebrate locality of Iharkút (Hungary)

“…Although calculation of gas and water conductance is not possible due to the fragmentary nature of all eggshells, the thinness of MT I combined with a moderate to high density of pores and blindly ending pneumatic cavities (Table 2), and the wide pores relative to overall shell thickness suggest that the eggs were deposited in a buried nest, as reconstructed for most dinosaurs (Williams et al 1984;Horner 2000;Deeming 2006), and probably representing the ancestral mode of egg-laying (Tanaka et al 2015).…”

Allometric scaling of seed retention time in seed dispersers and its application to estimation of seed dispersal potentials of theropod dinosaurs

“…In addition, carnivorous dinosaurs could have dispersed seeds, either by accidental consumption of seeds or via their consumption of herbivorous animals; this has been confirmed in some extant vertebrates (Nogales et al , van Leeuwen et al ). Theropod dinosaurs are direct ancestors of extant birds, and therefore, extrapolations based on trait allometry for extant birds is a commonly used and effective approach for estimating these dinosaurs’ traits (Sato et al , Tanaka et al ). Although extant crocodiles, which are descendants of archosaurs, are occasionally used to infer the ecology of extinct dinosaurs (Seebacher et al ), recent advances in dinosaur ecology have demonstrated that extant birds are closer to theropod dinosaurs in their physiology, such as homeothermy, their behaviour (Gillooly et al ), diversified diets (Zanno and Makovicky ) and bipedal locomotion (Farlow et al ).…”