palaeoecology

palaeoecology Palaeoecology is the study of the interactions of organisms with each other and with their environment in the geological past. It thus borrows heavily from the modern discipline of ecology although its emphases are different. Modern biologists can sample populations on scales of years and describe environments in detail, while palaeontologists are limited by the data they can collect and generally work on timescales of thousands or millions of years. Despite these restrictions, palaeoecology is important because of its value in helping to reconstruct ancient environments and in understanding fossils as once-living organisms.

The ecosystem is the largest unit of ecological study and consists of a portion of the physical environment, however large or small, together with all the organisms it contains. Within this the habitat is the environment in which the organism lives; its niche is its position in the habitat, including its relationship with other organisms. Study may be at the level of the individual or encompass populations of two or more individuals or communities of two or more species. Modern organisms are grouped according to the role they play in the flow of energy through the ecosystem. Primary producers such as plants convert nutrients and light into organic compounds, which are then consumed by herbivores. In their turn the herbivores are eaten by carnivores or by scavengers and, eventually, all organisms are broken down by bacteria into nutrients that return to the environment.

In order to study the ecology of fossil organisms, palaeoecological inference is used extensively. This uniformitarian approach is based on the assumption that the general laws governing the functioning of organisms have not changed with time. Producers, herbivores, carnivores, and decomposers were present in the past, and although the complexity of ecosystems has increased, the laws governing the flow of energy through them are assumed not to have changed. Some interactions, particularly predator–prey relationships, are independent of inference from modern communities; thus, for example, teeth marks in an ammonite show that it was bitten by a mosasaur. Other relationships require more inference, as in the study of ancient reefs. Modern reefs consist mostly of corals that live in symbiotic relationship (in which both gain an advantage) with algae. The algae need sunlight to photosynthesize and the corals provide the framework to hold them near the surface. Similar reefs can be seen in Cenozoic and Mesozoic rocks and a similar relationship can be inferred.

The functions of various features in fossils can also be inferred by comparison with modern organisms; in many instances, however, these features may be unknown in modern taxa. In order to interpret these so that an understanding of adaptation and mode of life can be developed a coherent methodology such as the paradigm approach is used. In this system optimum structural designs for all possible functions of the feature are developed and the design that appears most similar is considered most likely to be correct.

Other areas of palaeontology are important in the study of palaeoecology. Taphonomy deals with the processes that affect an organism from death to burial, and is necessary for an understanding of the extent to which the preserved organisms accurately reflect the living communities. Ichnology deals with tracks and trace fossils and therefore provides evidence of the soft-bodied members of communities that otherwise leave no record.

David K. Elliott