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 collections 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.

The reciprocal interaction of angiosperm evolution and tetrapod herbivory

“…Frequency of attack must have been related to the energy requirement of herbivore populations, a quantity determined by multiplying the energy requirement of an individual by the number in the population. Such calculations by previous authors suggest that the rate of biomass consumption in dinosaur and modern large herbivore faunas is not radically different (Bakker, 1972;Farlow, 1976;Weaver, 1983). Thus, we presume that frequency of attack was also similar.…”

Dynamic Energy and Mass Budgets in Biological Systems

“…Farlow [268] gives an empirical scaling exponent of 0.88, but value 1 also fits the data well. For endotherms especially, a scaling exponent of somewhat less than 1 is expected for weight as the independent variable, because of the increase in volumespecific weight, as explained.…”

“…It relates to the question of whether or not dinosaurs were endotherms, which is still a topic of considerable controversy [269]. The blood vessels in bones [42], the bone structure [49], and predator/ prey ratios [268] resemble those of birds and mammals, the general morphology points to a very active life style [41], all indications that dinosaurs were endotherms [209]; the absence of respiratory turbinates in dinosaurs is recently taken as evidence that they were ectotherms with no need to recover water from their breath [792], the micro-distribution of oxygen isotope in bones led some to conclude that the body temperature varied considerably in a 5-Mg Tyrannosaurus [633], and many speculations about growth and reproduction rates of dinosaurs are based on the low ectothermic levels [152]. The problem of sufficient heat loss in big dinosaurs in hot mesozoic climates was stressed by others.…”

Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA)

“…Flighted birds typically have a higher BMR than do flightless birds of the same body mass, and the largest birds are flightless (McNab 2009a). Such complications aside, differences between endotherms and non-avian reptiles are also seen in the scaling of field metabolic rate (FMR: Nagy 2005) or food consumption rates (Farlow 1976(Farlow , 1990Peters 1983;Nagy 2001) against body mass.…”