Glossary

**Nesting behavior** refers to the suite of reproductive behaviors in dinosaurs and other animals encompassing nest construction, egg arrangement, incubation (brooding), and post-hatching parental care. In paleontology, dinosaur nesting behavior is reconstructed from fossilized nest structures, egg clutch arrangements, adult skeletons preserved in brooding postures atop nests, and the co-occurrence of hatchling or juvenile remains with adults. The diversity of nesting strategies ranges from burying soft-shelled eggs in moist substrate for passive incubation to constructing mound nests using decomposing plant material for warmth, to partially open nests where feathered theropods directly brooded their eggs with body heat. These differences correlate with eggshell mineralization (soft vs. hard), body size, and phylogenetic position within Dinosauria. The study of nesting behavior is critical for understanding dinosaur reproductive physiology, social organization, and the evolutionary origins of parental care, providing key evidence that many behaviors characteristic of modern birds originated in non-avian dinosaur lineages.

Precocial and altricial describe the two ends of a developmental spectrum characterizing the degree of physical maturity and functional independence that offspring possess at hatching or birth. Precocial young are born or hatched in a relatively advanced state—with open eyes, a body covering of down or fur, the ability to thermoregulate, and enough musculoskeletal strength to move and often forage independently within hours or days. Altricial young, by contrast, emerge in a highly underdeveloped condition—typically naked or nearly so, with closed eyes, minimal locomotor capacity, and complete dependence on parental feeding and thermoregulation for survival. The spectrum is not a simple binary: intermediate categories include semi-precocial (mobile but nest-bound and parent-fed, e.g., gulls), semi-altricial (downy but immobile, e.g., raptors), and superprecocial (fully independent from hatching, e.g., megapodes). In extant birds, precociality is associated with energy-dense eggs that support prolonged embryonic development, whereas altriciality is linked to smaller eggs with lower caloric content but rapid postnatal growth fueled by intensive parental provisioning. These contrasting strategies reflect evolutionary trade-offs between prenatal investment, predation risk, food availability, and brain development. In paleontology, the precocial–altricial framework is extensively applied to non-avian dinosaurs to reconstruct parenting behavior, nesting ecology, and life-history strategy from evidence such as bone histology, limb proportions, eggshell structure, and nest associations.