Living dinosaurs (birds) and their closest living relatives (crocodilians) share many derived features of reproduction; these are probably synapomorphies of Archosauria and so would be expected to be found in all extinct dinosaurs:
Fossil dinosaur eggs and nests found in the rock record, as have embryos of most major dinosaur clades.
ALL non-avian dinosaur eggs are basketball-sized or smaller: NO dinosaur hatched from eggs the size of people!!
Some dinosaur nests associated with covered mats of vegetation: probably helped to keep warm (as in croc nests).
Some dinosaurs (maniraptorans) found in “brooding position” over nests; unlikely to be found in dinosaurs which are too large (i.e., tyrannosaurids, hadrosaurids, sauropods, etc.) or lacking feathers (non-coelurosaurs).
Most primitive modern birds are ground nesters; suggests that tree nesting did not evolve until well into the modern bird (Aves) radiation.
Dinosaurs tend to have nests of about a dozen or so eggs each: more than found in modern birds, less than in (for example) turtles. This is regardless of size: troodontids to titanosaurids!
Implies that unlike placental mammals, dinosaurs could produce a dozen or so offspring a year regardless of size; among placental mammals, larger body size means LONGER gestation periods.
Two main potential life habits upon hatching:
Some evidence of these habits in hatchling dinosaurs:
Dinosaur growth rate: VERY HIGH compared to typical reptiles, particular in big dinosaurs. Estimates (based on bone “growth rings”, and other features) indicate only 3-7 years for big ceratopsids and hadrosaurids to reach adult size, and only 10 years for big sauropods (e.g., Apatosaurus) to reach adult size.
(In contrast, big crocodilians from the Late Cretaceous seem to have taken 50 years or so to reach the same size as big hadrosaurs).
Since most animal populations stay generally stable over time, more baby dinosaurs died before reaching adult size than in typical populations of modern birds or mammals (imagine herd of antelope where every female produced a litter of 12 every year!).
Four main sources of information for forming behavior hypotheses:
Some behaviors to consider:
Important to consider the difference between intraspecific and interspecific displays:
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