Ecological Interactions in Dinosaur Communities: Influences of Small Offspring and Complex Ontogenetic Life Histories

Daryl Codron,Chris Carbone,Marcus Clauss,Andrew A Farke

doi:10.1371/journal.pone.0077110

Abstract

Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs’ successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well.

Highlights

Modern terrestrial vertebrate systems are dominated by mammals, whereas birds and herpetiles are smaller-bodied and less conspicuous components of our landscapes
Dinosaurs and mammals differ in multiple aspects of biology, life history, and ecology [1,2], but it is the difference in reproductive strategies that is likely to have most relevance to arising ecological trends [3,4,5,6]
An interesting pattern emerges if data for all oviparous Mesozoic vertebrates are assessed together - because of the small maximum size of Mesozoic birds, the overall Mesozoic terrestrial vertebrate mass-species richness (M-S) distribution is bimodal, and a size gap appears in the size range of several to roughly a thousand kg (Figs. 1a and g; see Codron et al [4])

Summary

Introduction

Modern terrestrial vertebrate systems are dominated by mammals, whereas birds and herpetiles are smaller-bodied and less conspicuous components of our landscapes. Dinosaurs and mammals differ in multiple aspects of biology, life history, and ecology [1,2], but it is the difference in reproductive strategies that is likely to have most relevance to arising ecological trends [3,4,5,6]. Dinosaurs, like their living descendents (birds), and extant herpetiles, were oviparous - numerous eggs and nesting sites have been described from the fossil record, and in some cases these have even been associated with particular taxa [5,6,7,8,9]. Since a species’ survivorship schedule is strongly linked to the growth rate of populations [16], dinosaur populations surely experienced growth and dynamics that were different than those of mammals

Methods

Results

Conclusion