TWO LATE TRIASSIC BRACHIOPOD BIODIVERSITY HOT SPOTS

The Late Triassic is a unique time period for articulate brachiopods because they appear to make a comeback after being nearly decimated during the end-Permian mass extinctions. This resurgence pattern is evident in many taxonomic diversity studies, however detailed paleoecological studies of this Late Triassic brachiopod trend have not been completed. Extensive paleoecological investigations are needed to: 1) define the nature of the resurgence; 2) to determine whether this pattern was unique to particular environments; and 3) to establish if the pattern differed from Paleozoic brachiopod communities or whether the rise in diversity was caused by a small-scale, global reappearance of Paleozoic brachiopod communities in a variety of environments. To obtain a global pattern of brachiopod resurgence, a literature review was completed and data sets have been chosen based upon published evidence of temporal taxonomic changes between brachiopods and bivalves. Initial investigation includes the Luning Formation of Nevada and the Kössen Formation of Austria. Paleoecological analyses (i.e., review of abundance and sedimentological data) of these two areas indicate that the bivalve and brachiopod biofacies are derived from separate paleoenvironments. The brachiopod-dominated biofacies tend to have preferentially formed in moderately agitated, carbonate shelf environments while the bivalve-dominated biofacies favored more distal, low energy environments with a less stable substrate. This preliminary investigation suggests that Late Triassic articulate brachiopods were able to again dominate some benthic environments on a local scale. Thus, it is likely that the Late Triassic brachiopod “resurgence” was a unique ecological, geographical, and environmental event rather than a small-scale reiteration of Paleozoic brachiopod-dominated communities.