20 Ancient mariner albatross soared over Zealandian oceans

Aves, Procellariiformes: Plotornis archaeonautes

Aotearoa New Zealand is a biodiversity hotspot for seabirds with more than a quarter of all seabird species breeding in the New Zealand archipelago today. Indeed, Aotearoa has endemic species within four of the five major seabird groups: Charadriiformes (e.g. tarapirohe, black-fronted tern Chlidonias albostriatus), Procellariiformes (e.g. toroa, southern royal albatross Diomedea epomophora), Sphenisciformes (e.g. hoiho, yellow-eyed penguin Megadyptes antipodes) and Suliformes (e.g. kawau pāteketeke, New Zealand king shag Leucocarbo carunculatus). The fifth group, Phaethontiformes, includes a species that is native to New Zealand but not endemic (Amokura or red-tailed tropicbird, Phaethon rubricauda). Seabirds are an important link between marine and terrestrial ecosystems by bringing nutrients onshore which then contribute to the growth of plants. The question of how long seabirds have been an important part of the ecosystems of Aotearoa is investigated by studying the fossil record. In 2024 the fossil record for albatrosses in Zealandia was revealed to be at least 22 million years old.

Beak from the ancient mariner albatross Plotornis archaeonautes (specimen OU 22690). The ancient mariner albatross was a similar size to some of the smallest albatrosses living today. Image source: Figure 2 in D Ksepka, A Tennyson, M Richards and RE Fordyce (2024) A new species of Plotornis (Aves, Pan-Diomedeidae) from the earliest Miocene of New Zealand, which is licensed under CC BY-NC-ND 4.0. Image credit: RE Fordyce.

The partial skeleton of the fossil albatross Plotornis archaeonautes was discovered in 2010 during a field trip to a limestone quarry in South Canterbury led by Ewan Fordyce. Preparation of the fossil showed the skeleton was from a bird about the size of the smallest living species of albatross (i.e. Laysan albatross Phoebastria immutabilis, with an approximately two metre wingspan). The beak of the fossil albatross was slender compared to living species, which the researchers suggested could correspond with a more fish-intensive diet than the squid-intensive diet of albatrosses today. Recognising the fossil as a new species of Plotornis provided the earliest uncontroversial record of albatrosses in the fossil record of the Southern Hemisphere, and greatly increased the known geographic range of Plotornis to encompass both hemispheres.

Researchers haven’t yet arrived at a consensus on how long the New Zealand archipelago has been a biodiversity hotspot for seabirds. Clear supporting evidence would be needed to show that a diversity of seabird species can be consistently found in the fossil record of Aotearoa across deep time through to modern day. Although just one individual, the discovery of Plotornis archaeonautes was an important piece in this much larger story.

—Written by Daniel B Thomas