A Consideration of the Trophic Dynamics of a Late Cretaceous Large‐Dinosaur Community (Oldman Formation)

Abstract

The Late Cretaceous Oldman Formation comprises sediments that were deposited along the margin of a great inland sea that covered much of the western interior of North America. The environment of deposition appears to have been tracts of fluvial marshes that separated “islands” of higher, drier ground. The climate was probably warm—temperate, and it is suggested that upland plant communities were parkland—like in aspect. The large dinosaurs of this community comprised animals that were between a hippopotamus and a large African elephant in adult weight. Some workers have suggested that dinosaurs had metabolic rates comparable to those of living birds or mammals. By extrapolating from the food consumption rates of these living endotherms it is possible to obtain crude estimates of the ingestion rates of endothermic dinosaurs. Similar extrapolations from the ingestion rates of living reptiles and amphibians provide estimates of the ingestion rates of ectothermic dinosaurs. By deriving an empirical equation relating the ratio of annual secondary productivity/average annual biomass to adult weight in living mammals, and employing estimates of adult weight and biomass for the herbivorous dinosaur populations, it is possible to estimate the annual secondary production of endothermic Oldman herbivorous dinosaurs. If the body weight vs. production/biomass relation derived for mammals can be applied to ectothermic tetrapods, it is possible to estimate annual secondary production of ectothermic dinosaur populations. These calculations suggest that the annual secondary production of endothermic herbivorous dinosaurs would have been insufficient to meet the food requirements of an endothermic carnivorous dinosaur population as large as is preserved in the Oldman Formation. However, ectothermic carnivorous dinosaurs would have been easily able to make energetic ends meet. Unfortunately, the situation is complicated by the possibility that carnivores are overrepresented in collection from the Oldman. Because of this, I cannot presently decide between ectothermy and endothermy in dinosaurs on the basis of methods presented in this paper. Alternative methods that may be more successful in this regard are discussed. It is hoped that as paleontologists collect fossils from an ecological point of view the methods presented in this paper can be employed to make realistic statements about the trophic dynamics of ancient vertebrate communities.