EVOLUTIONARY AND BIOGEOGRAPHIC PATTERNS OF TRILOBITES DURING THE END ORDOVICIAN MASS EXTINCTION EVENT

Abstract

The end Ordovician mass extinction event is believed to have been caused by a geologically brief, sudden onset glacial period that interrupted a period of extreme greenhouse conditions. The cause of this icehouse is a matter of contention, but recent a recent work proposes that a nearby gamma-ray burst could have affected the Earth's atmospheric chemistry and pushed the climate from a greenhouse into an unstable icehouse. Survivorship patterns of trilobites and their larval forms appear to agree with this theory. In order to further explore the Ordovician extinction, I conducted three individual paleontological studies to test macroevolutionary and biogeographic patterns of trilobites across the extinction. The first study is a phylogenic and biogeographic analysis of the family Homalonotidae Chapman 1890, the second is a similar analysis of the subfamily Deiphoninae Reed 1913, and the third is a GIS study of species ranges of the subfamily Deiphoninae.