Kairuku (genus), a genus of extinct penguins from the Paleocene to early Eocene epochs, containing three species: Kairuku kauaensis, Kairuku waitakiensis, and Kairuku grebneffi. The name is derived from the Māori word meaning “diver who returns with food.”
The first fossils of this genus were discovered in New Zealand in 1978, and it was not until 1984 that they were properly described and named by paleontologists Alan J. D. Tennyson and Trevor H. Worthy. The type species is Kairuku kauaensis, named for the Kauaeranga Valley on the North Island where its remains were found; the other two species are named for the Waitaki River area on the South Island (Kairuku waitakiensis) and Lake Grebnev on Sakhalin Island in Russia (Kairuku grebneffi).
All three species of Kairuku probably shared a similar lifestyle and ecology to modern penguins, being well-adapted to an aquatic existence with webbed feet, feathers adapted for waterproofing, and streamlined bodies. They likely fed on small fish, squid, and crustaceans. However, there are some anatomical differences between them and modern penguins which suggest that they may have had different feeding strategies; for example, their long beaks may have been more suited to catching fast-moving prey than today’s penguins’ stubby ones.
Although all three species of Kairuku were once thought to be monotypic (containing only one subspecies each), further fossil finds have since revealed that there was actually considerable variation within each species. For example, K. kauaensis is now known to have ranged in size from around 1 metre (3 ft 3 in) tall to almost 2 metres (6 ft 7 in). It is unclear why such large variations existed within what would otherwise appear to be fairly uniform animals; possibilities include sexual dimorphism or regional ecological differences.
Fossils of all three species of Kairuku have been found in marine deposits associated with Antarctica; however, it is uncertain whether they actually lived there or whether their remains simply ended up there after floating northwards on currents after death. What is certain is that they inhabited a very different world from today’s penguins; at the time when they lived, global temperatures were considerably higher than they are now due to greenhouse gases released into the atmosphere by volcanic activity, and Antarctica was not yet covered in ice sheets as it is today.