What was the world like when Kairuku penguins lived? It was quite different from today. Zealandia – a formal name for proto-New Zealand bore little resemblance to its modern day configuration. Sea level in the region was relatively higher, both because the main islands of Zealandia were not as uplifted as they are today and because there were no permanent polar ice sheets, leaving more water in the oceans instead of locked away as ice. Thus, shallow seas submerged large swathes of the South Island,where Kairuku fossils have been recovered. It was a great place to be a penguin. The small emergent parts of the South Island would have been safe breeding grounds, given the remoteness from other land masses and lack of terrestrial predators to disturb nests.
Fossil bones of Kairuku penguins are found in a rock formation called the Kokoamu Greensand. As the name implies, this formation is primarily composed of greenish sedimentary rock formed when seafloor sediments were compressed and became lithified. Several types of sediments are mixed in different layers, including fine quartz sand, calcareous sands, and clays. The sandstones are heavily bioturbated – that is, mixed up by the borrowings of animals. The seafloor was teaming with life, both on the surface and beneath. Some of the most common invertebrate fossils in the Kokoamu Greensand are shells of the brachiopod Waiparia. Brachiopods are shellfish that belong to a whole different class than the bivalve mollusks (clams, oysters, and relatives) that make up most modern shellfish faunas. Waiparia belong to the family Terebratellidae, which I remember fondly from my undergraduate paleontology labs for their spaceship-like shapes. These shellfish would have anchored themselves into the seafloor with a holdfast and used their filtering lophophores to collect food particles from the current. I’ve been told that brachiopods are a poor dietary choice, both in terms of nutrients provided and taste. More familiar and probably more delicious mollusks also lived in the region and are found as fossils in the Kokoamu Greensand. Scallops are fairly common, and sea snails and clams were present too.
Kairuku also had some rather unwelcome neighbors. Among these were many species of sharks, the grandest of which was Carcharodon angustidens. This species was a relative of the Great White Shark and reached about 9m (27 feet) in length. Such predators would have been dangerous even to fully grown Kairuku penguins. Another predatory group was the Squalodontia, an extinct family of shark-toothed dolphins. Unlike the conical teeth of living dolphins, squalodonts had serrated teeth, with multiple small cusps along the edges. Waipatiidae were another interesting fossil group of predatory dolphins. One of the amzing things about the species Waipatia maerewhenua is its procumbant incisors. These front teeth point forward from the snout, rather than pointing down like the teeth of a normal dolphin. You can see an artist reconstruction of a beached Waipatia maerewhenua in the background of the Kairuku waitaki artwork that accompanied our paper by scrolling down. This dolphin was not huge like Carcharodon angustidens, but was probably dangerous to at least juvenile Kairuku penguins as well as smaller contemporary penguin species like Duntroonornis parvus. You an read more about this amazing fossil dolphin and other New Zealand fossils at the University of Otago Geology Museum’s website.