Species New to Science's Journal

[PaleoOrnithology • 2025] Tadorna rekohu • Ancient DNA and Morphometrics reveal A New Species of extinct insular Shelduck (Anatidae: Tadorninae) from Rēkohu Chatham Islands, Aotearoa New Zealand

Tadorna rekohu

Rawlence, Lubbe, Adams, Shepherd, Cole, Knapp, Llamas, Wood, Mitchell & Tennyson, 2025

Rēkohu shelduck || DOI: doi.org/10.1093/zoolinnean/zlaf069

Abstract

The Rēkohu Chatham Islands, 785 km east of mainland Aotearoa New Zealand, exhibit high levels of species endemism. Prior to human settlement, the islands supported a rich waterfowl fauna comprising at least eight anatid species. Here we describe a new extinct duck from Holocene fossil bone deposits on the Chatham Islands. Geometric morphometric analyses and phylogenetic analysis of complete mitogenomes confirm that the Rēkohu shelduck (Tadorna rekohu sp. nov.) was the sister-taxon to the pūtangitangi paradise shelduck Tadorna variegata (Gmelin, 1789) from mainland New Zealand. The ancestors of the Rēkohu shelduck colonized the Chatham Islands around 390 000 years ago during the Late Pleistocene. Comparatively short, robust wing bones and long leg bones indicate that the species was flight-reduced relative to their mainland congener. The presence of Rēkohu shelduck bones in early Moriori midden deposits suggests its extinction was due to over-hunting prior to the later European and Māori settlement of the islands in the 19th century.

dispersal, island evolution, New Zealand, palaeogenetics, Pleistocene, Tadorna

Artistic reconstruction of a female Rēkohu shelduck (Tadorna rekohu) showing the darker plumage common in birds isolated on islands.

Artwork by Sasha Votyakova, © Te Papa CC BY 4.0

Systematic palaeontology

Anseriformes Wagler, 1831

Anatidae Leach, 1819

Tadorninae Reichenbach, 1849

Tadornini Reichenbach, 1849

Tadorna Boie, 1822

Tadorna rekohu Rawlence, Lubbe, Adams, Shepherd, Cole, Knapp, Llamas, Wood, Mitchell, Tennyson sp. nov.

Common name: Rēkohu shelduck

Type locality: Maunganui, Chatham Island.

Etymology: After the Moriori name for the Chatham Islands, New Zealand, where T. rekohu formerly occurred. The name was gifted by the Hokotehi Moriori Trust, who represent the Indigenous people of Rēkohu Chatham Islands.

Diagnosis: A species of Tadorna with different proportions to T. variegata and differing from T. variegata in the following osteological features and allometries:

Cranium: The skull of T. rekohu is longer and has a smaller interorbital width.

Humerus, ulna, radius, and carpometacarpus: The humeri of T. rekohu are on average shorter, with more robust proximal and distal ends. The ulnae and carpometacarpi are on average shorter in T. rekohu, and the proximal radius width is on average larger in T. rekohu.

Humerus to femur ratio: The femur of T. rekohu is longer relative to the humerus total length. The ratio of mean humerus to femur length in T. rekohu ranges from 1.92 to 1.96 (associated skeletons) compared to 2.00–2.11 and 2.02–2.18 in female and male T. variegata, respectively.

Femur and tarsometatarsus: The femora and tarsometatarsi of T. rekohu are longer on average.

Nicolas J Rawlence, Pascale Lubbe, Amy L Adams, Lara D Shepherd, Theresa L Cole , Michael Knapp, Bastien Llamas, Jamie R Wood, Kieren J Mitchell and Alan J D Tennyson. 2025. Ancient DNA and Morphometrics reveal A New Species of extinct insular Shelduck from Rēkohu Chatham Islands. Zoological Journal of the Linnean Society. 204(3); zlaf069. DOI: doi.org/10.1093/zoolinnean/zlaf069 [25 July 2025]