The helochelydrid turtle Helochelydra nopcsai from the Early Cretaceous (late Barremian – early Aptian) fissure fills of Balve, North Rhine-Westphalia, Germany, including a large sample of granicones

Abstract

Early Cretaceous (late Barremian – early Aptian) fissure fill deposits near Balve, North Rhine Westphalia, Germany, have yielded a rich continental vertebrate fauna over the course of the last two decades. More than 250 fragmentary specimens, including more than 150 osteoderms (i.e., granicones), represent the late Early Cretaceous helochelydrid Helochelydra nopcsai , which had previously been reported from the UK, France, and Spain. The new material mostly differs from that from the type section by exhibiting a reduced to absent entoplastral scute and by displaying distinct cranial scute sulci, both of which are interpreted as intraspecific variation. Although morphological insights are limited, the new material reveals that the visceral cavity extends anteriorly and posteriorly to the bridge, a relatively novel feature previously reported for an eclectic mix of compsemydids, pleurosternids, and other helochelydrids. The available sample of granicones reveals great shape diversity, but a morphometric analysis concludes that no distinct morphotypes exist.