THE NATURE OF EVOLUTIONARY RADIATIONS WITH A SPECIAL FOCUS ON DEVONIAN CALMONIID TRILOBITES

Abstract

Trilobites were a diverse group of arthropods that left an extensive fossil record which are today used today to study macroevolutionary patterns and processes. A new species and form of olenelloidea trilobites (Nevadella keelensis n. sp. and Esmeraldina rowei) are described from the lower Cambrian Sekwi Formation, Canada. One particular clade of trilobites, the Devonian calmoniid trilobites of the Malvinokaffric Realm, was hailed as a classic paleontological example of an adaptive radiation. Three aspects of the radiation were examined in detail: diversification rates, biogeography, and morphological change. The rates of speciation calculated from stratigraphy were highest when sea level was lowest suggesting causal effect of abiotic factors in speciation. A phylogenetic biogeographic analysis indicated a geographically complex area, and this geographic complexity created various opportunities for speciation via allopatry through sea level changes. The geometric morphometric analysis of morphological change during the radiation did not show a signal of ecological filling. Ultimately, adaptive radiations--including some classic cases--may be caused primarily by abiotic factors of speciation.