Kairuku is an extinct genus of penguin.[1] It contains three species, K. grebneffi, K. waitaki [2] and K. waewaeroa.[3] This taxon is known from bones from 27 MYA (late Oligocene), from the Kokoamu Greensand Formation of New Zealand.[1] It was historically referred to as Palaeeudyptes.[1]
The species name waewaeroa is from Māori waewae - "legs", and roa - "long", referring to the elongated hind limbs.[3]
K. grebneffi was named after Andrew Grebneff, a paleontologist from the University of Otago who died in 2010.[4]
The fossils of Kairuku waewaeroa were found within the Glen Massey formation (34.6–27.3 Ma) in the North Island of New Zealand.[3]
Kairuku is one of the most completely known genus of Paleogene penguins. Described species are larger than modern emperor penguin which stood around a meter,[1] K. grebneffi stood 1.28 metres (4.2 ft) tall,[1] and K. waewaeroa is even larger with height up to 1.38 metres (4.5 ft).[3] Unnamed species called Glen Murray fossil penguin is estimated to have a height 2 to 20% taller than K. grebneffi.[5]
Kairuku grebneffi were nearly 1.5 metres (4.9 ft) long and stood 1.3 metres (4.3 ft) tall.[4] Adult individuals weighed an estimated 60 kilograms (130 lb), 50% more than modern emperor penguins.[6] K. grebneffi had the longest humerus bone of any penguin extant or attested to in the fossil record.[4] The bird had a longer bill and more slender body compared to living penguins.[7] Relative to its body size, its flippers were longer and probably more flexible than those of extant species.[7][8] The bird had short, thick legs, but overall, looked much like a modern penguin "from a distance."[7][8] K. grebneffi is distinguished from its sister species K. waitaki primarily on the basis of vertebrae spacing and by having a straight tipped bill, compared to the curved tip of K. waitaki.[4] Additionally, all known specimens of K. grebneffi are larger, although small sample size prevents that from being a diagnostic characteristic.[4]