Multiple exceptionally preserved fossils from the Paleocene Waipara Greensand inform the diversity of the oldest stem group Sphenisciformes and the formation of their diving adaptations

Abstract We report new stem group sphenisciforms (ancestral penguins) from the Paleocene of the Waipara Greensand (Canterbury, New Zealand), and describe four new genera and species (Daniadyptes primaevus gen. et sp. nov., Waiparadyptes gracilitarsus gen. et sp. nov., Archaeodyptes waitahaorum gen. et sp. nov., Waimanutaha kenlovei gen. et sp. nov.) and a small species, which is tentatively assigned to the taxon Kupoupou. New material of Muriwaimanu tuatahi includes the first complete skull of this species. The fossils show previously unknown features of the earliest penguins, such as well-developed basipterygoid processes and a long hind toe, and for the first time gastroliths are preserved in a stem group sphenisciform. The very small D. primaevus as well as W. gracilitarsus and A. waitahaorum exhibit plesiomorphic features, which support a position outside a clade formed by M. tuatahi and more crownward taxa. The penguins from the Waipara Greensand show that during early penguin evolution selective forces mainly acted on the wing, pectoral girdle, and foot morphology, whereas the greatly elongated beak remained relatively unchanged for more than 20 Myr. Furthermore, the fossils support the New Zealand region as the centre of origin of sphenisciforms and document multiple radiations of stem group Sphenisciformes throughout the Cenozoic.