Data from: Largest-known fossil penguin provides insight into the early evolution of sphenisciform body size and flipper anatomy

<p>Recent fossil discoveries from New Zealand have revealed a remarkably diverse assemblage of Paleocene stem group penguins. Here, we add to this growing record by describing nine new penguin specimens from the late Paleocene (upper Teurian local stage; 55.5–59.5Ma) Moeraki Formation of the South Island, New Zealand. The largest specimen is assigned to a new species, <em>Kumimanu fordycei</em> sp. nov., that may have been the largest penguin ever to have lived. Allometric regressions based on humerus length and humerus head width of extant penguins yield mean estimates of a live body mass in the range of 159.4 kg (95% CI: 143.4 kg–179.6kg) and 148.7 kg (95% CI: 143.4kg–180.0kg), respectively, for <em>Kumimanu fordycei</em>. A second new species, <em>Petradyptes stonehousei</em> gen. et sp. nov., is represented by five specimens and was slightly larger than the extant emperor penguin <em>Aptenodytes forsteri</em>. Two small humeri represent an additional smaller unnamed penguin species. Parsimony and Bayesian phylogenetic analyses recover <em>Kumimanu</em> and <em>Petradyptes</em> crownward of the early Paleocene mainland NZ taxa <em>Waimanu</em> and <em>Muriwaimanu</em>, but stemward of the Chatham Island taxon <em>Kupoupou</em>. These analyses differ, however, in the placement of these two taxa relative to <em>Sequiwaimanu</em>, <em>Crossvallia</em>, and <em>Kaiika</em>. The massive size and placement of <em>Kumimanu fordycei</em> close to the root of the penguin tree provide additional support for a scenario in which penguins reached the upper limit of sphenisciform body size very early in their evolutionary history, while still retaining numerous plesiomorphic features of the flipper.</p>