The craniomandibular anatomy of the early archosauriform Euparkeria capensis

Archosauria (birds, crocodilians and their extinct relatives) form a major part of terrestrial ecosystems today, with over 10 000 living species, and came to dominate the land for most of the Mesozoic (over 150 Myr) after radiating following the Permian–Triassic extinction. The archosaur skull has been essential to this diversification, itself diversified into myriad forms. The archosauriform Euparkeria capensis from the Middle Triassic (Anisian) of South Africa has been of great interest since its initial description in 1913, because its anatomy shed light on the origins and early evolution of crown Archosauria and potentially approached that of the archosaur common ancestor. Euparkeria has been widely used as an outgroup in phylogenetic analyses and when investigating patterns of trait evolution among archosaurs. Although described monographically in 1965, subsequent years have seen great advances in the understanding of early archosaurs and in imaging techniques. Here, the cranium and mandible of Euparkeria are fully redescribed and documented using all fossil material and computed tomographic data. Details previously unclear are fully described, including vomerine dentition, the epiptergoid, number of premaxillary teeth and palatal arrangement. A new diagnosis and cranial and braincase reconstruction is provided, and an anatomical network analysis is performed on the skull of Euparkeria and compared with other amniotes. The modular composition of the cranium suggests a flexible skull well adapted to feeding on agile food, but with a clear tendency towards more carnivorous behaviour, placing the taxon at the interface between ancestral diapsid and crown archosaur ecomorphology, corresponding to increases in brain size, visual sensitivity, upright locomotion and metabolism around this point in archosauriform evolution. The skull of Euparkeria epitomizes a major evolutionary transition, and places crown archosaur morphology in an evolutionary context

The first definite record of a Valanginian ichthyosaur and its implications on the evolution of post-Liassic Ichthyosauria

A complete ichthyosaur rostrum, with 124 associated teeth, was recently discovered in Laux-Montaux locality, department of Drôme, southeastern France. The associated belemnites and ammonites indicate a late Valanginian age (Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone) for this fossil, which consequently represents the first diagnostic ichthyosaur ever reported from Valanginian strata. This specimen also represents the first occurrence of Aegirosaurus outside the Tithonian (Upper Jurassic) lithographic limestones of Bavaria (southern Germany). Tooth morphology and wear pattern suggest that Aegirosaurus belonged to the “Pierce II/ Generalist” feeding guild, which was hitherto not represented in post-Liassic ichthyosaurs. Most Late Jurassic ichthyosaurs actually crossed the Jurassic-Cretaceous boundary

Disruption of playa-lacustrine depositional systems at the Permo-Triassic boundary : evidence from Vyazniki and Gorokhovets on the Russian Platform

Permo-Triassic sections at Vyazniki and Gorokhovets provide evidence on terrestrial events at, or close to, the Permo-Triassic boundary, the time of the largest ever mass extinction. The sedimentary succession records the overrun of a muddy playa–lacustrine depositional system by major channel belts transporting sand-grade sediments. Biostratigraphy of sections at Vyazniki and Gorokhovets (Zhukov Ravine) shows that this event occurred either at the very end of the Permian or 8 m above in the sections. The timing and nature of this event, which records increased sediment flux from the Ural Mountains, is closely comparable with that from the Southern Uralian Foreland Basin. The Vyazniki and Gorokhovets sections are 800 km from the mountain front and in a separate depositional basin, which strengthens the case that increased sediment flux from the Urals at the Permo-Triassic boundary is related to devegetation of upland catchments (increasing sediment yield) and a switch toward low-frequency but high-magnitude discharge events (increasing sediment delivery). The interbedding of fluvial and aeolian deposits provides further evidence for climatic instability and extremes in the Early Triassic. Supplementary material: Detailed reports on the ostracodes and fossil fish remains from the Zhukov Ravine sections are available at http://www.geolsoc.org.uk/SUP18402