Journal of Paleontology, 87(5), 2013, p. 854–880 Copyright Ó 2013, The Paleontological Society 0022-3360/13/0087-854$03.00 DOI: 10.1666/12-153 A NEW PALEOECOLOGICAL LOOK AT THE DINWOODY FORMATION (LOWER TRIASSIC, WESTERN USA): INTRINSIC VERSUS EXTRINSIC CONTROLS ON ECOSYSTEM RECOVERY AFTER THE END-PERMIAN MASS EXTINCTION RICHARD HOFMANN, MICHAEL HAUTMANN, AND HUGO BUCHER Pala¨ontologisches Institut und Museum, Universita¨tZu¨rich, Karl-Schmid-Strasse 4, 8006 Zu¨rich, Switzerland, ,
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[email protected]. ABSTRACT—The Dinwoody Formation of the western United States represents an important archive of Early Triassic ecosystems in the immediate aftermath of the end-Permian mass extinction. We present a systematic description and a quantitative paleoecological analysis of its benthic faunas in order to reconstruct benthic associations and to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition throughout the earliest Triassic of the western United States. A total of 15 bivalve species, two gastropod species, and two brachiopod species are recognized in the study area. The paleoecological analysis shows that the oldest Dinwoody communities are characterized by low diversity, low ecological complexity and high dominance of few species. We suggest that this low diversity most likely reflects the consequences of the mass extinction in the first place and not necessarily the persistence of environmental stress. Whereas this diversity pattern persists into younger strata of the Dinwoody Formation in outer shelf environments, an increase in richness, evenness and guild diversity occurred around the Griesbachian–Dienerian boundary in more shallow marine habitats.