Bird or maniraptoran dinosaur? A femur from the Albian strata of Spitsbergen

The first known fossil vertebrate found in the Lower Cretaceous of Spitsbergen (Svalbard, Arctic Norway) is presented and described. The specimen, a femur, was collected from the Zillerberget member of the Carolinefjellet Formation at Schönrockfjellet in 1962 and was recently re-discovered. The bone is referred to ?Avialae based on a combination of characters, including extreme thinness of the cortex, a well-developed head, and the presence of a patellar sulcus. From biostratigraphic analysis, it is demonstrated that the bone comes from the lower part of the middle Albian. This find is important because the Early Cretaceous fossil record of Avialae remains poorly documented in most parts of the World and is non-existent in Arctic strata. A general overview of the geology and stratigraphy of the Lower Cretaceous in Spitsbergen is presented in order to provide context for the fossil occurrence, with a particular focus on the Aptian and Albian sedimentary system and with the first-ever report on the entire stratigraphy on the east face of Schönrockfjellet.