Abstract

Here are described phytosaurs from thin fluvial overbank sandstones interbedded with lacustrine mudstones from the Late Triassic Malmros Klint Formation of the Fleming Fjord Group (central East Greenland). The discovery yielded more than 150 disarticulated bones and teeth from young to adult specimens, belonging to, at least, four individuals. The fossils mostly composed of teeth and postcranial elements, permit the recognition of a new species of Mystriosuchus, M. alleroq with a quadratojugal with a L-shape, which anterior suture trends anterodorsally, and a tripartite degree of heterodonty serving as autapomorphies. Humeral histology of the midshaft reveals a rather compact cortex that surrounds a cancellous medullary region followed by a remodeling zone containing scattered secondary osteons. Primary bone tissue is parallel-fibred tissue with a moderate to low vascular density. The cortex is cyclically interrupted by distinct growth marks indicating a seasonal environment. A change in growth rate from moderate to low is documented within the outer cortex, indicating that one of the individuals was close to maturity. Mystriosuchus has formerly been known as an exclusively European taxon. The new findings support a strong European faunal influence in East Greenland during the Late Triassic with other taxa, such as temnospondyls and archosaurs. The confirmed Mid-Late Norian age of Mystriosuchus provides an additional and important age constraint for the vertebrate-bearing portion of the Malmros Klint Formation.