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

Tadorna Boie, 1822 View in CoL

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

Common name: Rēkohu shelduck

Zoobank registration: urn:lsid:zoobank.org:act:

Holotype: NMNZ S.32830 ( Figs 7–8), associated skeleton, collected bv Phil Millener on the 20 Januarv 1993. Te skeleton consists of cranium, mandible, sternum, L humerus, R

ulna, L radius, LR carpometacarpus, LR femur, R tibiotarsus, and four vertebrae.

Holotype measurements: skull total length 103.6 mm; interorbital width (in the middle) 8.1mm; humerus total length 130.1 mm; humerus head depth 9.7mm; proximal humerus width 26.8 mm; humerus shaf width (mid-shaf) 9 mm; distal humerus depth 10.9 mm; distal humerus width 18.8 mm; ulna total length 122.9 mm; proximal radius width 7.4 mm; carpometacarpus total length 74 mm; femur total length 66.5 mm; femur minimum shaf width (mid-shaf) 6.3 mm; tibiotarsus minimum shaf width (mid-shaf) 5.2 mm; distal tibiotarsus width 12.6 mm.

Type locality: Maunganui, Chatham Island.

Etymology: Afer the Moriori name for the Chatham Islands, New Zealand, where T. rekohu formerlv occurred. Te name was gifed bv 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:

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

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

3. Humerus to femur ratio: Te femur of T. rekohu is longer relative to the humerus total length. Te 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 , respectivelv.

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

Paratypes: NMNZ S.25009, associated skeleton (25 bones: cranium, L mandible, LR quadrate, 13 vertebra, R ulna, R radius, pelvis, LR femur, LR tibiotarsus, R tarsometatarsus), collected from Waitangi West , Chatham Island , bv Phil Millener on the 9 Januarv 1988 ; NMNZ S.25011, associated skeleton (seven bones: R coracoid, L humerus, LR ulna, L radius, LR tarsometatarsus), collected from Waitangi West , Chatham Island , bv Phil Millener on the 9 Januarv 1988 ; NMNZ S.26435, associated skeleton (13 bones: R coracoid, R scapula, LR humerus, L ulna, LR radius, LR carpometacarpus, Lfemur , Ltibiotarsus , twopedalphalanges), collected from Tahatika Stream , Chatham Island , bv Phil Millener on 21 Januarv 1988 ; NMNZ S.29453, associated skeleton (34 bones: mandible, six vertebra, two ribs, furcula, LR coracoid, LR scapula, LR humerus, LR ulna, LR radius, LR carpometacarpus, three alar phalanges, pelvis, LR femur, LR tibiotarsus, LR tarsometatarsus, two pedal phalanges), collected from Maunganui Beach , Chatham Island , bv Phil Millener on 19 Februarv 1991 .

Paratype measurements: NMNZ S.25009: interorbital width (in the middle) 6.9mm; ulna total length 109.5 mm; proximal radius width 6.8 mm; femur total length 59.3 mm; femur maximum shaf width (mid-shaf) 7.1 mm; femur minimum shaf width (mid-shaf) 6.3 mm; tibiotarsus maximum shaf width (mid-shaf) 6.1 mm; tibiotarsus minimum shaf width (mid-shaf) 5.1 mm; distal tibiotarsus width 12.3 mm; tarsometatarsus total length 61.1 mm. NMNZ S.25011: coracoid total length 49.9 mm; articular humeral facet width of coracoid 6.5 mm; humerus total length 109.9 mm; humerus head depth 8.7 mm; proximal humerus width 23.5 mm; humerus shaf width (mid-shaf) 7.6 mm; distal humerus depth 9.6 mm; distal humerus width 16.2 mm; ulna total length 100.1 mm; proximal radius width 6.4 mm; tarsometatarsus total length 60 mm. NMNZ S.26435: coracoid total length 59.0 mm; articular humeral facet width of coracoid 8.0 mm; proximal scapula width 16.0 mm; humerus total length 134.9 mm; humerus head depth 10.2 mm; proximal humerus width 27.3 mm; humerus shaf width (mid-shaf) 9.5 mm; distal humerus depth 11.6 mm; distal humerus width 19.8 mm; ulna total length 125.4 mm; proximal radius width 7.7 mm; carpometacarpus total length 76.7 mm; femur total length 69.1 mm; femur maximum shaf width (mid-shaf) 7.7 mm; femur minimum shaf width (mid-shaf) 6.7 mm; tibiotarsus maximum shaf width (mid-shaf) 7.3 mm; tibiotarsus minimum shaf width (mid-shaf) 5.7 mm; distal tibiotarsus width 13.5 mm. NMNZ S.29543: fucula acrocoracoidial process maximum width 5.3 mm; coracoid total length 50.8 mm; articular humeral facet width of coracoid 6.9 mm; proximal scapula width 14.1 mm; humerus total length 117.4 mm; humerus head depth 8.8 mm; proximal humerus width 24.1 mm; humerus shaf width (mid-shaf) 8.4 mm; distal humerus depth 9.9 mm; distal humerus width 17.7 mm; ulna total length 109.0 mm; proximal radius width 6.5 mm; carpometacarpus total length 65.9 mm; femur total length 61.2 mm; femur maximum shaf width (mid-shaf) 7.0 mm; femur minimum shaf width (mid-shaf) 6.3 mm; tibiotarsus maximum shaf width (mid-shaf) 6.2 mm; tibiotarsus minimum shaf width (mid-shaf) 5.1 mm; distal tibiotarsus width 12.1 mm; tarsometatarsus total length 63.8 mm.

Distribution: Formerlv the Chatham Islands, New Zealand. Bones presumed to be of T. rekohu have been recorded from late Quaternarv deposits on Chatham, Pit (see Supporting Information, Table S1), and Mangere Islands ( Tennvson and Millener 1994). Given T. rekohu was flight-reduced, not flightless, it is likelv that this species also occurred on all the main islands in the group (e.g. South East Island).