Large-sized Ichthyosaurs from the Lower Saurian Bone Bed (Early Triassic) of the Vikinghøgda Fm., Marmierfjellet, Spitsbergen

Abstract

The remains of large-sized, derived ichthyosaurs are collected and described from the Lower Saurian bone bed of the Early Triassic Vendomdalen Member, Vikinghøgda Formation of Marmierfjellet, Spitsbergen, with an updated review of the stratigraphy. The Lower Saurian bone bed has a thickness of approximately 1 m and can be followed laterally for 3.5 km along the western and norther flank of Marmierfjellet. During the field seasons of 2014 and 2015, 571 fragmentary to complete vertebrae, more than 400 limb and girdle fragments and 250 jaw and skull fragments from ichthyopterygians were collected and identified. The specimens were collected as isolated elements from the Lower Saurian bone bed and given individual GPS-coordinates. An updated stratigraphical log of the bone beds in Flowerdalen and a detailed log of the Lower Saurian bone bed is presented. Similar excavations have not been undertaken since Wiman first described the bone beds at Marmierfjellet in 1910. The Lower Saurian bone bed fauna contains a dense population of mid- to large-size ichthyosaurs. In this study, diagnostic remains of Cymbospondylus Leidy, 1868 and Pessopteryx Wiman, 1910 are identified, and 48 bone elements referred to Ichthyosauria indet. are described. An updated overview of the ichthyopterygian faunal assemblage of the Lower Saurian bone bed is provided and compared with an updated review of the ichthyopterygian fauna of the Grippia Niveau. The possibility that the large-sized, diagnostic bone elements of Pessopteryx and Cymbospondylus may share a common generic identity is discussed.