简介

My research is primarily concerned with the shark faunas during the Neogene polytaxic maximum (NPM). The NPM began following a prolonged period of very low global temperatures in the Late Oligocene (Chattian) about 26-27 Mya. By the late Early Miocene (Burdigalian) global temperatures and atmospheric carbon dioxide levels increased until they were comparable to those of today. This period was characterized by a marked diversification and expansion of marine communities. The end of the NPM began with episode of global cooling 3.6-2.0 Mya in the Late Pliocene (Piacenzian) and concluded with a major turnover in marine biotas 2-1 Mya. During the NPM shark faunas underwent two fundamental changes. The first was faunal modernization where middle trophic levels previously dominated by lamniform sharks with tearing-type teeth (i.e., tall, slender crowns) were replaced by carcharhiniforms with more versatile cutting-clutching dentitions (i.e., serrated, blade-like teeth in the upper jaw and slender, erect teeth in the lower jaw). This rise of the carcharhiniforms appears to have been associated with the diversification of marine invertebrates and teleosts in the tropics beginning in the Late Paleogene and continuing through much of the later Neogene.