Kairuku grebneffi

Kairuku grebneffi were nearly 1.5 metres (4.9 ft) long and stood 1.3 metres (4.3 ft) tall.[1] Adult individuals weighed an estimated 60 kilograms (130 lb), 50% more than modern emperor penguins.[2] K. grebneffi had the longest humerus bone of any penguin extant or attested to in the fossil record.[1] The bird had a longer bill and more slender body compared to living penguins.[3] Relative to its body size, its flippers were longer and probably more flexible than those of extant species.[3][4] The bird had short, thick legs, but overall, looked much like a modern penguin "from a distance."[3][4] 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.[1] Additionally, all known specimens of K. grebneffi are larger, although small sample size prevents that from being a diagnostic characteristic.[1]

K. grebneffi likely used its slender beak to spear fish and squid.[3] It likely was able to dive deeper and swim farther than living penguins.[2] Predators of the bird likely included sharks and Squalodons.[3]

K. grebneffi lived in what is now New Zealand late in the Oligocene period, roughly 25-27 million years ago.[2] At the time, most of the area was ocean, with a few isolated islands.[2] It is believed that these rock outcrops provided safe breeding grounds and easy access to rich food resources in the surrounding seas.[2] K. grebneffi lived alongside at least four other penguin species. It is likely that each species fed on different kinds of fish.[5]

K. grebneffi was among of the last of the giant penguins.[3] The cause of K. grebneffi's extinction is unknown, but was probably related to "the drastic change in paleoenvironment" according to Tatsuro Ando, one of the scientists who classified the penguin.[3] Other possibilities include the arrival of new predators and increased food competition.[2]

The first Kairuku bones were discovered in 1977 by Ewan Fordyce, although they were not identified as such at the time.[2] In February 2012, an international team of scientists led by Fordyce and Daniel Ksepka reconstructed a K. grebneffi skeleton using a few "key specimens" from the Kokoamu Greensand of the North Otago and South Canterbury districts of New Zealand.[1][2] The specimens used represent some of the most complete skeletons found of any extinct penguin, and thus provide valuable insight into the reconstruction of all extinct penguins.[1] The king penguin was used as a guide during reconstruction.[2]

K. grebneffi was named after Andrew Grebneff, a paleontologist from the University of Otago who died in 2010.[1] The genus name Kairuku is a Māori-language word meaning "diver who returns with food". The holotype was collected in 1991 from a drainage area of the Waipati stream, a tributary of the Maerewhenua River.[1]