Marine vertebrates from the Hartland Shale (Upper Cretaceous: Upper Cenomanian) in southeastern Colorado, USA

► This study is the first report of the vertebrate fauna of the Hartland Shale, USA. ► Twenty-five marine vertebrate taxa (24 fishes and one reptile) are identified. ► Apateodus and Cimolichthys mark geologically the oldest record for the genera. ► The Hartland fauna represents the onset of the 'Niobrara fauna' that followed. ► Identified vertebrates are mostly carnivores, providing new palaeoecological insights.