ALBERT

Beschreibung: A bstract 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. This incipient recovery towards the end of the Griesbachian is in accordance with observations from other regions and thus probably represents an interregional signal. In contrast to increasing richness within communities (alpha-diversity), beta-diversity remained low during the Griesbachian and Dienerian in the study area. This low beta-diversity reflects a wide environmental and geographical range of taxa during the earliest Triassic, indicating that the increase of within-habitat diversity has not yet led to significant competitive exclusion. We hypothesize that the well-known prevalence of generalized taxa in post-extinction faunas is primarily an effect of reduced competition that allows species to exist through the full range of their fundamental niches, rather than being caused by unusual and uniform environmental stress.

Beschreibung: Palynostratigraphy across the Permian–Triassic of the Salt Range and Surghar Range area remains poorly known because of the predominance of unsuitable facies and preservation (Nammal, Chhidru, Chitta-Landu and Narmia). Dolomite and limestone in the basal Mianwali Formation prevented the establishment of a palynostratigraphic scheme for the basal Early Triassic ( Hermann et al. 2012 ). Based on the study of a new Permian–Triassic section in the Amb valley where siltstone layers are intercalated in the basal Mianwali Formation (Kathwai Member), we describe a new record of palynological assemblages from the uppermost Permian Chhidru Formation and the lowermost part of the Early Triassic Mianwali Formation. The latest Permian Chhidru 2 sporomorph association occurs in the uppermost part of the Chhidru Formation, the so-called ‘white sandstone unit’. It is marked by the dominance of bisaccate pollen grains (mainly Protohaploxypinus spp.) and cavate trilete spores (mainly Kraeuselisporites spp.). Here, the previously described lowermost Triassic palynozone PTr 1 is subdivided into two subzones. PTr 1a assemblages are described from the Griesbachian Kathwai Member. They are characterized by continued high bisaccate pollen grain abundances and the presence of the lycopod genera Lundbladispora spp. and Densoisporites spp. In these assemblages, typical ‘Permian taxa’ and typical ‘Triassic taxa’ are mixed. The composition of the middle Dienerian PTr 1b assemblages corresponds to the previously described PTr 1 assemblage from Nammal and Chitta-Landu. Lundbladispora spp. and Densoisporites spp. account for ca. 80% of the total assemblage in PTr 1b. Although the Griesbachian assemblages record a decrease in diversity, the middle Dienerian assemblages represent the poorest assemblages of the studied Permian–Triassic interval. Reduviasporonites occurs only sporadically throughout the Amb succession.

Beschreibung: The Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygian Birgeria (Birgeriidae), attributed to B . americana new species and Birgeria sp. Birgeria americana n. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.72–1.85m, it is among the largest birgeriids. We confirm that Birgeria encompasses species with either two or three rows of teeth on the maxilla and dentary, and suggest that species with three well-developed rows are restricted to the Early Triassic. From the latest Smithian of Palomino Ridge, we present a three-dimensional, partial skull of the longirostrine predator Saurichthys (Saurichthyidae). This and other occurrences indicate that saurichthyids were common in the western USA basin. From the early late Spathian of Crittenden Springs, we describe a posterior body portion (Actinopterygii indet.). This find is important given the paucity of Spathian osteichthyan sites. We provide a summary of Early Triassic vertebrate occurrences in the United States, concluding that vertebrate fossils remain largely unstudied. The presence of predatory vertebrates in subequatorial latitudes during the Smithian confirms that Early Triassic trophic chains were not shortened and contradicts the ‘equatorial vertebrate eclipse’.

Beschreibung: The marine Triassic rocks of Nevada are well known for their ichthyosaur finds, and a number of new genera and species were described from this state. Based on a few vertebrae, Leidy (1868) erected a new Middle Triassic ichthyosaur genus, Cymbospondylys, with two species, C. petrinus and C. piscosus. The type material of C. petrinus came from the Prida Formation of the southern Humboldt Range, and that of C. piscosus from the Favret Formation of the New Pass Range.