The functional morphology of dinosaur eggshells is important paleontologically for interpreting the egg-laying, physiology, and nesting behaviors of dinosaurs. For example, a high number of large-diameter pores translated to a greater ease of conductance of gases between the embryo and the outside world. The calculated values of conductance from porosities in dinosaur eggshells are 8 to 16 times those of avian eggshells, which is different enough to postulate an adapted purpose for this function in dinosaur eggs. Most avian eggs are laid in an open environment, where they are not covered by either sediment or vegetation. In contrast, the high conductance values of dinosaur eggs strongly suggest that they were placed in environments with low O2 and high amounts of CO2 and H2O. These presumptions imply that the dinosaur eggs were probably buried in some medium, such as in a nest structure. Furthermore, crystals in an eggshell may manifest externally as surface ornamentations, forming lengthwise ridges. These ridges probably represent microscopic channels for gas exchange along the long axis of a vertically-oriented egg.
An assemblage of eggs in close association with one another in the fossil record is often regarded as part of a clutch, meaning that these eggs represent one egg-laying episode. Dinosaur clutches apparently ranged from two to perhaps as many as 35 eggs, which is comparable to numbers laid by modern birds. This range is in contrast to the large numbers produced by crocodilians or other reptiles; for example, sea turtle egg clutches can contain more than 100 eggs. Furthermore, for modern reptiles, variation in clutch size is positively correlated with body size, hence larger individuals will lay more eggs. Whether a similar relationship existed for some dinosaurs is relatively unexplored, although better correlation of certain eggs with egglayers of known body size could lead to an answer.
Many modern reptiles abandon their clutches after laying them, leaving the juveniles to fend for themselves. However, some crocodilians stay close by their nests and will help to excavate any buried eggs as the juveniles in them begin to hatch. Most birds also remain near their clutches and will typically assume a seated position over the eggs for protection and insulation, a behavior called brooding. Brooding has been interpreted on the basis of dinosaur skeletons found sitting on egg clutches. These finds include the theropods Oviraptor and Troodon (Chapter 9) and also can be inferred from the close association of juvenile and adult remains of the same dinosaur species (Maiasaura and Psittacosaurus: Chapters 11 and 13, respectively). Interestingly, because brooding is more typical of birds than reptilians, this behavior is often explained as a trait that physiologically relates dinosaurs to birds (Chapter 15).
A dinosaur egg assemblage probably represents eggs laid by a single mother of the same dinosaur species. However, modern cuckoo birds (Cuculus canorus) and a few other species of birds will lay their eggs in the nest of a different species. Thus all of the eggs in a nest should not always be assumed as coming from the same parent. So far, only one possible piece of evidence would suggest that some dinosaurs engaged in cuckoo-like behavior: a nest from the Late Cretaceous of Mongolia contained the embryonic remains of two different dinosaurs, Oviraptor and possibly Velociraptor. However, taphonomic factors, such as selective transportation and deposition of hydrodynamically similar eggs from different nests, cannot be discounted (Chapter 7). Another hypothesis for explaining the juxtaposition of different eggs in the same nest is that a nest site could have been constructed by one of the two species. In such cases, a nest could have been re-used later by another species while it still contained previous unhatched eggs.
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