next up previous
Next: McMillan et al. - Up: Special Symposium - From Previous: Leighton & Sawyer -

Lockwood - Extinction and the evolutionary history of Late Cretaceous and early Cenozoic veneroid bivalves

Extinction and the evolutionary history of Late Cretaceous and early Cenozoic veneroid bivalves

Rowan Lockwood

Department of Geology, The College of William and Mary, PO Box 8795, Williamsburg, VA 23187, rxlock@wm.edu

Although the causes of mass extinctions in the fossil record have been studied in detail, recoveries have received little attention until recently. This study focuses on the effects of two extinction events, the end-Cretaceous (K/T) and end-Eocene (E/O), on long-term patterns of morphology and ecology in veneroid bivalves. Systematic and stratigraphic data were collected for 140 subgenera of veneroids from the Late Cretaceous through Oligocene of North America and Europe. Morphological data were collected for 1236 specimens representing 101 subgenera. Extinction selectivity and preferential recovery were assessed with respect to morphology, and by extension, burrowing ecology in these bivalves. Veneroids underwent a substantial extinction at the K/T boundary, although diversity recovered to pre-extinction levels by the early Eocene. Despite the severity of the K/T extinction, I found little evidence of morphological or ecological selectivity. In contrast, the K/T rebound was significantly biased towards smaller taxa with more elliptical shells and relatively deeper pallial sinuses (i.e., towards relatively deeper, faster burrowers). The E/O event was considerably smaller and the recovery interval biased towards larger veneroids. It is clear that the K/T, although short-lived in geological time, exerts a stronger influence on diversity, morphology, and ecology in veneroids than the E/O event. The morphological and ecological effects of the K/T are not tied to the extinction itself, but to the recovery that follows. The K/T recovery initiates a trend towards deeper burrowing that helps to establish veneroids as one of the most abundant and successful groups of modern marine bivalves.


next up previous
Next: McMillan et al. - Up: Special Symposium - From Previous: Leighton & Sawyer -
Peter Roopnarine 2005-04-12