Stepwise Faunal Change during Evolutionary Turnover: A Case Study from the Neogene of Curaçao, Netherlands Antilles
Assemblages of reef corals through the Middle Miocene to Late Pliocene Seroe Domi Formation in Curaçao are described and statistically analyzed to document patterns of change in these associations during a Late Pliocene Caribbean-wide episode of accelerated faunal turnover. The data are based on large field collections made systematically at 73 localities within a sequence of bedded siliciclastics and coralgal limestones near Sint Michielsberg. Geologic age dates are newly determined for the sequence using high-resolution chronostratigraphic methods including paleomagnetics and strontium-isotope analyses, and the localities are subdivided into five locality-groups-Middle Miocene flatiron, Late Miocene salina-base, Mio-Pliocene salina-top, Early to Late Pliocene ridges, and Late Pliocene sea-cliff. Using a consistent set of morphologic characters, a total of 99 species are identified in the collections, and their occurrences are compared with first and last species occurrences reported elsewhere in the Caribbean. Frequencies of Stylophora, Acropora, and extant species are compared among the five locality-groups using non-parametric statistical tests. Occurrence matrices (99 species x 35 localities) are assembled for the collections using both relative abundance codes and presence-absence data, and average linkage cluster analysis and detrended correspondence analysis are performed to further examine the nature of the differences in the fauna among locality-groups. Interpretations of the results suggest that assemblages in the three older locality-groups (flatiron, salina-base, salinatop) are composed of >75% pre-turnover species, whereas assemblages in the youngest group (sea-cliff) are composed of 63% post-turnover species. The ridges localities (44% post-turnover species) represent a transitional step between the two extremes and contain assemblages in which dominant members of the old and new faunas co-occurred. Age estimates for the transition correspond generally with those reported for a similarly prolonged faunal transition in the Limon Group of Costa Rica. The flatiron localities differ distinctively in faunal composition from the other four locality-roups, which overlap in composition. Wide variation is observed within each locality-group. This variation is unrelated to stratigraphy and can be only partially attributed to environmental and taphonomic factors. Instead, it appears to be caused by the irregular, patchy local distributions often characteristic of reef-builders and, together with the overlap among locality-groups, suggests that faunal change was not coordinated and that species were independently distributed through the sequence.
Published Article/Book Citation
Palaios, 13:2 (1998) pp. 170-188.