Supplementary information for: A new tiny fossil penguin from the Late Oligocene of New Zealand and the morphofunctional transition of the penguin wing

The Late Oligocene is a period of high penguin diversity, following major
changes in the marine environment at the Eocene/Oligocene boundary and
prior to the emergence of crown penguins in the Miocene. Historically, a
large morphological gap existed between the most crownward Platydyptes
among the Oligocene penguins from New Zealand and the Early Miocene stem
penguins such as Palaeospheniscus and Eretiscus from South America. Here
we describe a new species that contributes to filling this gap. Pakudyptes
hakataramea gen. et sp. nov. is the earliest tiny penguin, overlapping in
size with the smallest extant species, the little penguin Eudyptula minor.
Its distinctive combination of a well-developed proximal end of the
humerus and a rather archaic elbow joint provides clues to the evolution
of penguin wings. Phylogenetic analysis indicates that penguin wings
evolved rapidly from the Late Oligocene to the Early Miocene, together
with the acquisition of morphofunctional and hydrodynamical
characteristics that enable the excellent swimming ability of modern
penguins. As an indicator of aquatic adaptation, bone microanatomy also
shows a comparable structure to that of Eudyptula. The appearance of the
smallest body size and the evolution of modern wings may have led to the
ecological diversity of modern penguins, which confirms the importance of
Zealandia in penguin evolution.