DIVERSITY AND DISTRIBUTION PATTERNS IN SOME TRILOBITES MIMIC DYNASTINE BEETLES

Trilobites from localities with high taxonomic diversity are noted for having ornate and exuberant morphologies. Two particularly notable examples of high diversity and structural complexity come from the Lower to Middle Ordovician of Russia, and the Late lower to Early Middle (Emsian-Eifelian) Devonian of Morocco. What made these instances possible? Were they due to extrinsic factors such as climate and habitat, or intrinsic factors such as species and sexual selection?

In order to test if patterns could be seen that would correlate with any of those causes, we compared diversity and distribution patterns for trilobites in the Middle Ordovician and Middle Devonian to the distribution and diversity pattern of dynastine beetles. Dynastine scarabs were chosen as a model group for comparison due to their outwardly similar exuberant morphologies and known correlation with sexual selection as well as the very detailed locality distribution and diversity data compiled for North and central America due to the work led by Brett Ratcliffe.

Beetle diversity data was harvested from published works summarizing the diversity and distribution of dynastines in the Americas. Trilobite paleogeographic distribution, habitat, and diversity data was gathered from the Paleobiology Database as well as published literature. These data were compiled into an ArcGIS dataset and compared spatially with climate, habitat and geography.

Analyses of these factors show that trilobite distribution patterns are similar to those of dynastine scarabs, with higher diversity aligning with optimal climates, and in situations of high diversity a rise in exuberant morphologies. This suggests that the degree of exotic structures seen is likely due to species and sexual selection rather than optimal environment alone.