T399 The Road to Recovery—The Nature of Biotic and Geochemical Cycles During the Early Triassic

Wednesday, 30 October 2013
1:00 PM - 5:00 PM
Room 504

TURNOVER OF DOMINANT BENTHIC TAXA IN THE EARLY TRIASSIC

Paper number: T399-4
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

Punctuated perturbations and fluctuating conditions after the end-Permian mass extinction event led to highly uneven benthic marine communities in the Early Triassic. Encroachment of dysoxic conditions on shelf communities, as well as global temperature spikes, suppressed recovery of community complexity until the Middle Triassic in most marine settings. A group of invertebrates termed the “disaster taxa” of the Early Triassic have been previously observed as highly abundant, widespread, and ecologically dominant in the Early Triassic, and include the bivalve genera Claraia, Eumorphotis, Promyalina and Unionites, and the brachiopod genus “Lingula”. Presented here is a stage by stage quantification of disaster taxa dominance in the Early Triassic, as well as the newly developed disaster taxon index incorporating both abundance and distribution for representing ecological importance. Abundance data from North American and European fossil collections, representing the Eastern Panthalassic and Western Tethyan Ocean Basins, are analyzed using this new dominance metric as well as standard measurements of ecological importance.

Our results show that disaster taxa experience a peak in ecologically importance during the first 1 Ma interval following the end-Permian extinction event, specifically, they represent a high proportion of individuals (approx. 75%) reported from Paleobiology Database abundance data and bulk collections from the field. In the Smithian and Spathian stages of the Early Triassic, disaster taxa are reduced in ecological importance. Claraia and “Lingula”, which are associated with dysaerobic facies, are diminished in importance in the Smithian. Despite the reduced importance of the disaster taxa as a group, community unevenness remains surprisingly high when new taxa take over as the dominant group after the Dienerian. This turnover suggests changing ecological responses to abiotic events and may indicate a shift in the importance of low oxygen conditions to high temperature regimes resulted in the suppressed recovery and persistent high dominance faunas. Ongoing work will seek to link high resolution geochemical signals of environmental perturbations with community ecological responses to explore the implications of the Early Triassic turnover of dominant taxa.