Wednesday 30th July

12 – 1 pm

Rm 312.222

Ken McNamara

Department of Earth Sciences, University of Cambridge

Effects of environmental changes on the evolution and extinction of Late Devonian trilobites, northern Canning Basin, W.A.

Abstract

The Frasnian-Famennian Virgin Hills Formation represents fore reef facies deposited as part of the extensive Late Devonian reef system that fringed the south-western Kimberley Block in Western Australia. It contains a rich trilobite fauna dominated by proetids, and to a lesser extent, harpetids, phacopids, scutelluids and odontopleurids. To date 49 taxa have been described, 40 of these restricted to the Frasnian. Evolutionary trends in the Virgin Hills trilobites are dominated by reduction in body size and eye size, and, to a lesser extent, reduction in exoskeletal vaulting. Although recording no sedimentological signature, the fauna was strongly affected by the two globally recognized Kellwasser extinction events. The first, at the end of conodont Zone 12 affected taxa at the species and genus level. The second, at the end of Zone 13b, had a much greater impact, causing extinctions at the familial and ordinal levels. Evolutionary trends in the late Frasnian trilobites reflects selection for forms adapted to low nutrient conditions. The two intensive Kellwasser extinction episodes may reflect periodic massive inputs of nutrients from terrestrial into shallow marine environment.

Biography

Ken is an Adjunct Professor at Curtin; Senior Lecturer in Earth Sciences at the University of Cambridge; Director of the Sedgwick Museum, University of Cambridge, and Dean and Fellow of Downing College, Cambridge. He was adjunct at Curtin for many years, teaching palaeontology, when he was Head of Earth & Planetary Sciences at the WA Museum.