Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10-100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and hetero-

The replacement of the late Precambrian Ediacaran biota by morphologically disparate animals at the beginning of the Phanerozoic was a key event in the history of life on Earth, the mechanisms and the time-scales of which are not entirely understood. A composite section in Namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the Ediacaran-Cambrian boundary to 538.6-538.8 Ma, more than 2 Ma younger than previously assumed. The U-Pb-CA-ID TIMS zircon ages demonstrate an ultrashort time frame for the LAD of the Ediacaran biota to the FAD of a complex, burrowing Phanerozoic biota represented by trace fossils to a 410 ka time window of 538.99 ± 0.21 Ma to 538.58 ± 0.19 Ma. The extremely short duration of the faunal transition from Ediacaran to Cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the Phanerozoic.

A new marine fossil assemblage from the Early Triassic shows unexpected phyletic diversity and functional complexity.

ABSTRACT. Based on new material from the Upper Triassic Nayband Formation of east-central Iran and on type material from the Alpine Triassic, the taxonomy of the cementing bivalve families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae is examined and their phylogenetic relations are discussed. The Prospondylidae are characterized by the presence of an early pectiniform stage in their Palaeozoic genera which disappeared in most later forms due to ontogenetic pre-displacement of cementation. The Plicatulidae probably evolved from an ancestor within the Prospondylidae by the formation of strong crura, which allowed the reduction of the lateral part of the ligament. Their hinge was later modi®ed by shifting resilifer and crura in a ventral direction and by forming a secondary ligament dorsally. The emended genera Eoplicatula and Pseudoplacunopsis represent different early stages of this development. The species Eoplicatula parvadehensis sp. nov. and Pseudoplacunopsis asymmetrica sp. nov. from the Nayband Formation are described. The shell of some early Ostreidae is characterized by the lack of structural chambers and by the presence of an originally aragonitic inner shell layer. For such forms, the new genus Umbrostrea is proposed, and the new species Umbrostrea emamii and Umbrostrea iranica are described. The available data on shell microstructure as well as most conchological characters do not support a close relationship between Ostreidae, Plicatulidae and Dimyidae.

Latest Permian to the Middle Triassic mixed siliciclastic-carbonate shelf deposits of the northern Gondwana margin have been studied in four sections (Nammal, Chhidru, Chitta-Landu, and Narmia) in the Salt Range and Surghar Range of Pakistan. Sedimentological and palynofacies patterns combined with a high resolution ammonoid based age control have been used to assess environmental changes such as sea-level change, distance from the shore, and oxygenation conditions of the sections in the aftermath of the end-Permian mass extinction.The base and the top of the Early Triassic are marked by second order sequence boundaries (SRT1, SRT8). Within the Early Triassic two third order sequence boundaries could be delineated by means of palynofacies analysis and sedimentology, one near the Dienerian-Smithian (SRT2) and the second one near the Smithian-Spathian boundary (SRT5). The extinction event at the Smithian-Spathian boundary seems to be closely associated to the latter globally recorded sea-level low stand. Five additional sequences of undetermined order (SRT3, SRT 4, SRT5/1, SRT6, and SRT7) are reflected in the sedimentological record of the studied sections.The observed changes in the composition of the particulate organic matter (POM) indicate a general shallowing upward trend, which is modulated by smaller transgressive-regressive cycles supporting the sedimentologically defined sequences. The POM is mostly dominated by terrestrial phytoclasts and sporomorphs. The strongest marine signal is reflected by increased abundance of amorphous organic matter (AOM) in the lower part of the Ceratite Marls at Nammal (late Dienerian) and Chhidru (earliest Smithian) and the Lower Ceratite Limestone at Chitta-Landu (late Dienerian). AOM of marine origin is characteristic for deeper, distal basinal settings and is preferentially preserved under dysoxic and anoxic conditions, indicating reduced oxygen conditions during these intervals. Up-section transgressive events are reflected by increased numbers of acritarchs, reaching up to 50% of the POM. Well oxygenated conditions and low total organic carbon contents (TOC) continue up to the top of the Early Triassic (Mianwali Formation). The most pronounced terrestrial influx is expressed in the Middle Triassic.Organic carbon isotope data parallel the carbonate carbon isotope records from the Tethyan realm; therefore, they reflect real global changes in the carbon cycle independent of the OM composition. The biomarker study of the apolar hydrocarbons of three samples from the Nammal section indicates an enhanced bacterial productivity, especially in the Smithian and Spathian, reflected in high relative abundances of hopanes. POM, TOC data and redox sensitive biomarkers together with high resolution biostratigraphy demonstrate that well-oxygenated environmental conditions prevailed in the Early Triassic with the exception of the Dienerian to earliest Smithian interval. The POM assemblages of Late Permian to late Griesbachian age indicate well oxygenated conditions during this t...

(2014). Recovery of benthic marine communities from the end-Permian mass extinction at the low latitudes of eastern Panthalassa. Palaeontology, 57(3):547-589.

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