Clawed Lobster (Nephropidae) Diversity Through Time

Abstract

Clawed lobster diversity through time [Lower Cretaceous (Valanginian)–Recent] is compiled and interpreted herein. Species diversity trends are evaluated using raw numbers of species per geologic time unit (period, age) and also by using a variety of species-numbers normalization factors that address sampling biases. Species numbers are normalized for: 1) duration of time intervals (periods), 2) sedimentary rock exposure area per time intervals (periods), and 3) area under the Vail et al. (1978) sea-level curve (ages). The Vail curve method, new herein, normalizes for marginal/epicontinental sea coverage per age. By any measure; i.e., raw or normalized data, and over any time interval considered, shallow-dwelling (shelf depth) lobsters were significantly more diverse in the Cretaceous than in the Tertiary (e.g., 53 Cretaceous species vs. 16 Tertiary species, raw count; 18 Tertiary species if normalized for duration). Reduction in Tertiary lobster diversity seems due, in part, to mass extinction at the K/T boundary. However, lobster diversity rebounds in the Eocene, and it seems apparent that lower diversity of Tertiary lobsters is due more to post-Paleocene events than to K/T boundary events. The reduction in Tertiary fossil diversity seems largely explained by the lobsters' general abandonment of shelf depths in the Tertiary (ca. late Eocene–early Oligocene). Deep-dwelling lobsters are seldom collected as fossils, and their diversity history will never be known, but it seems clear that shelf-dwelling lobsters were significantly more diverse in the Cretaceous.