Triassic ichthyopterygian assemblages of the Svalbard archipelago: a reassessment of taxonomy and distribution

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Ichthyopterygians were amongst the most specialised lineages of secondarily aquatic amniotes; however, their origin and initial radiation remain obscure. The stratigraphically oldest and phylogenetically most basal taxa have been found in Early–Middle Triassic deposits throughout the northern hemisphere, but one of the earliest documented and arguably most important localities is the High Arctic Svalbard archipelago. Like many classic palaeontological sites, the Svalbard Triassic fossil-bearing horizons are plagued by inconsistent geological interpretations and taxonomic classifications. To resolve these conflicts, a comprehensive revision of the various ichthyopterygian assemblages was undertaken. The fossils were found to be distributed through three sequential rock units: the Olenekian Vikinghøgda Formation (six discernible taxa distributed over two distinct horizons), Anisian lower Botneheia Formation (two taxa) and the Ladinian–Carnian Blanknuten Member of the Botneheia Formation–Tschermakfjellet Formation (five taxa). Unfortunately, many of the specimens are non-diagnostic at species-level, although they do contribute a cohesive picture of marine faunal successions during the Early–earliest Late Triassic. Indeed, the Svalbard archipelago has produced one of the most diverse Early Triassic ichthyopterygian assemblages known worldwide, but is comparatively species poor throughout the early Middle Triassic, perhaps due to sampling biases.