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We review the available data on dinosaur life histories and examine the nature and magnitude of physiological, biophysical, and demographic factors that constrained life-history variation in this group.

Constraints arise from interdependencies among life-history characteristics and demographic characteristics. After a series of simulation studies of demographically imposed constraints, we conclude that life histories with age of first reproduction more than about 20 years are very unlikely and probably did not exist, even in very large dinosaurs.

In a separate set of simulations, we explored the nature and magnitude of physiological and ecological constraints on rates of resource acquisition and assimilation and on allocation of assimilated resources to growth. We find that it is unlikely large hadrosaurs and other large dinosaurs could transduce food into biomass rapidly enough to mature in less than about 5 years and that a more reasonable estimate is around 10 to 12 years. Our conclusions regarding the effects of demographic constraints on life history variation do not depend on mode of temperature regulation in these animals. The results of the simulations of energetic constraints depended only slightly on mode of temperature regulation.

An improved model of heat exchange with the environment is presented that is applicable to large animals. In addition, we examined the daily and seasonal dynamics of thermal energy exchange in juvenile and adult hadrosaurs in a simulated Campanian environment. We argue that the impact of constraints arising from nutritional mode (herbivory) on heat-balance models and, hence, on considerations of the suitability of particular environments to animals of particular body size must be considered. Our simulations suggest that adult hadrosaurs of body mass similar to that of Maiasaura could not have remained active throughout the winter in an environment approximated by our microclimate simulation. The most likely response to such an environment would be migration.

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