The implications of a dry climate for the paleoecology of the fauna of the Upper Jurassic Morrison Formation
In light of diverse geological evidence that indicates a seasonal, semiarid climate for the time of deposition of the Morrison Formation, one can assume these general environmental conditions for the purpose of reconstructing the ancient ecosystem. Wet environments that preserved plant fossils and some invertebrates and small vertebrates in the Morrison can be interpreted as representing local conditions limited in space and/or time. These elements of the biota and the smaller dinosaurs were probably restricted to such wetland areas at times of environmental stress. A diverse fauna of large, herbivorous, sauropod dinosaurs ranged throughout the environment. Although this seems to be inconsistent with an environment with sparse resources, large size confers physiologic advantages that are adaptive for just such conditions. The scaling effect of large size makes large herbivores very efficient relative to their size in needing proportionately less food and food of poorer quality than smaller herbivores. They can also survive starvation longer and travel more efficiently to reach widely separated resource patches. Although few in number at any time, the sauropod dinosaurs are locally abundant and seemingly ubiquitous in the fossil record of the Morrison Formation because of overrepresentation of their highly preservable remains in an attritional fossil assemblage.