THE ROLE OF CLIMATE IN DETERMINING VERTEBRATE FOSSIL PRESERVATION AND DISTRIBUTION PATTERNS

Differential preservation of plant and animal tissues due to environmental conditions is a well established phenomenon studied by archeologists, anthropologists, paleontologists, and forensic scientists. Some of these studies are beginning to determine how the chemical and physical interplay between organism remains and various modern environments lead to the preferential destruction of some tissues over others.

Using this information to make inferences in the fossil record is somewhat problematic. For example, not all environments are preserved equally well in the fossil record, and some appear to be absent altogether. In turn, environmental distribution is driven by global climate patterns, which have varied considerably in the past.

Little attention has been paid to how the interaction of environment-dependent tissue destruction and a biased representation of past environmental conditions affect our ecological, environmental and climatic reconstructions of the past. Identification of these biases and how they affect the patterns we observe are required for an accurate interpretation of the fossil record. Here I examine how these may affect our interpretation of Late Jurassic biotic reconstructions.

Using published fossil databases, comparison of dinosaur and plant distributions suggest that both reached peak taxonomic diversity in the middle latitudes, contrasting with the present diversity peak around the equator. However, the peaks are offset, with the plant peak occurring approximately 10˚ higher in latitude. This difference corresponds to a shift from seasonally dry to temperate biome, where one moves from taphonomic conditions favoring bone preservation to those favoring plant preservation. The question remains as to how reliable fossil diversity patterns are, in light of this type of large-scale bias. The current equator-centered diversity curve is assumed to be ancient, yet this Late Jurassic example suggests that diversity patterns may have shifted over time with changing climate conditions. On the other hand, changing climatic conditions may have shifted the focus of preservation bias. Further work utilizing sedimentological data and experimental work focused on environmental factors biasing tissue destruction will be necessary to tease apart the factors driving these patterns.