Partial skeleton from the Paleocene of New Zealand illuminates the early evolutionary history of the Phaethontiformes (tropicbirds)

Abstract

We describe a new stem group representative of the Phaethontiformes (tropicbirds) from the Paleocene Waipara Greensand in New Zealand. The fossil consists of a partial skeleton with a nearly complete skull and represents the first unambiguous record of the Phaethontiformes from the Paleocene of the Southern Hemisphere. Clymenoptilon novaezealandicum gen. et sp. nov. has a proportionally shorter pelvis than Prophaethon shrubsolei from the early Eocene London Clay and appears to have been less adapted to foraging in an aquatic environment at or below sea-level. It is furthermore distinguished from P. shrubsolei and Lithoptila abdounensis from the late Paleocene/early Eocene of Morocco in a proportionally smaller foramen magnum of the skull. Together with other plesiomorphic features, this suggests that C. novaezealandicum is the sister taxon of a clade including Lithoptila, Prophaethon and crown group Phaethontiformes, and as one of the oldest stem group phaethontiforms the new species may indicate a Southern Hemispheric centre of origin of tropicbirds. After a recently described bony-toothed bird, C. novaezealandicum is the second seabird species from the Waipara Greensand to show affinities to taxa from the early Paleogene of the Northern Hemisphere. The wide early Paleogene distribution of the Phaethontiformes stands in sharp contrast to the geographic restriction of coeval diving seabirds, and different factors appear to have limited the dispersal of aquatic and pelagic seabird taxa in the early Paleogene. Gerald Mayr [Gerald.Mayr@senckenberg.de], Senckenberg Research Institute and Natural History Museum Frankfurt, Ornithological Section, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany; Vanesa L. De Pietri [vanesa.depietri@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; Al Mannering [alman@slingshot.co.nz], Canterbury Museum, Rolleston Avenue, Christchurch 8050, New Zealand; Leigh Love [lvlove@xtra.co.nz], PO Box 49, Waipara 7483, New Zealand; Erica Crouch [e.crouch@gns.cri.nz], GNS Science, 1 Fairway Drive, Lower Hutt 5040, New Zealand; Catherine Reid [catherine.reid@canterbury.ac.nz], University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand; R. Paul Scofield [pscofield@canterburymuseum.com], Canterbury Museum, Rolleston Avenue, Christchurch 8050, New Zealand, and University of Canterbury, School of Earth and Environment, Private Bag 4800, Christchurch 8140, New Zealand.