Data from: New fossil penguins (Aves, Sphenisciformes) from the Oligocene of New Zealand reveal the skeletal plan of stem penguins

Three skeletons collected from the late Oligocene Kokoamu Greensand of New
Zealand are among the most complete Paleogene penguins known. These
specimens, described here as Kairuku waitaki gen. et sp. nov. and Kairuku
grebneffi sp. nov., reveal for the first time the unique proportions of a
giant fossil penguin and the morphology of many key elements of the stem
penguin skeleton associated with underwater flight, including the first
reasonably complete sternum, one of only two complete forelimbs and the
first described pygostyle. Relative proportions of the trunk, flippers and
hindlimbs can now be determined from a single individual, offering insight
into the body plan of stem penguins and improved constraints on size
estimates for 'giant' taxa. Kairuku is characterized by an
elongate, narrow sternum, a short and flared coracoid, an elongate narrow
flipper and a robust hindlimb. The pygostyle of Kairuku lacks the derived
triangular cross-section seen in extant Spheniscidae, suggesting the
rectrices attached in a more typical avian pattern and the tail may have
lacked the propping function utilized by living penguins. New materials
described here, along with restudy of previously described specimens,
resolves several long-standing phylogenetic, biogeographic and taxonomic
issues stemming from the inadequate comparative material of several of the
first-named fossil penguin species. An array of partial associated
skeletons from the Eocene-Oligocene of New Zealand historically referred
to Palaeeudyptes antarcticus or Palaeeudyptes sp. are recognized as at
least five distinct species: Palaeeudyptes antarcticus, Palaeeudyptes
marplesi, Kairuku waitaki, Kairuku grebneffi and an unnamed Burnside
Formation species