Pterodroma zinorum Rando et al., 2024

Pterodroma zinorum Rando et al. sp. nov.

urn:lsid:zoobank.org:act:69B8A7C7-875A-4D23-B3E8414785A6EED4.

Holotype: MCMa 23020.023 , a partial associated skeleton, including almost complete skull with premaxilla lacking palatinum and pterygoideum, left and right quadratum, 16 vertebrae, synsacrum, clavicula, a proximal fragment of the sternum, left and right coracoids, left and right scapula lacking distal part, right humerus, left and right ulna, left and right radius, right carpometacarpus, left phalanx proximalis digiti majoris, left phalanx distalis digiti majoris, left femur, distal fragment of right femur, proximal fragment of the right tibiotarsus, left tibiotarsus, left tarsometatarsus, and four pedal phalanges ( Fig. 2 View Figure 2 ; Supporting Information, Figs S1–S8).

Measurements of the holotype (mm): skull length: 66.3; skull height: 19.7; interorbital width: 8.7; culmen length: 16.5; coracoid length: 26; coracoid width: 17.4; right humerus length: 74.2; left ulna length: 76.5; right carpometacarpus length: 37; left femur length: 27; left tibiotarsus length: 49; left tarsometatarsus length: 30.2.

Type locality: Furna das Torres , Pico Island (Azores).

Horizon: Late Quaternary–Recent.

Distribution: The Azores archipelago (at least the islands of Graciosa, São Jorge, Pico, Terceira, and São Miguel).

Status: Extinct.

Etymology: The species’ name honours both the late Paul Alexander Zino and his son Francis Zino for their effort and contributions to the knowledge and conservation of Pterodroma species from Macaronesia.

Paratypes: MCMa 23021.023 , a partial associated skeleton including an almost complete skull with premaxilla lacking palatinum and pterygoideum, three fragments of the mandible, eight vertebrae, incomplete sternum, right humerus, left ulna, left radius, a proximal fragment of right radius, right carpometacarpus, left phalanx proximalis digiti majoris, right femur, right tibiotarsus, right tarsometatarsus, and two pedal phalanges.

MCMa 23022.023, a partial associated skeleton, including an almost complete skull with premaxilla lacking pterygoideum, left quadratum, three vertebrae, synsacrum, a proximal fragment of the sternum, left coracoid, a distal fragment of the right coracoid, left scapula, right humerus, right ulna, a distal fragment of the left ulna, a distal fragment of the left radius, right carpometacarpus, a distal fragment of the left carpometacarpus, right femur, left tibiotarsus, a distal fragment of the right tibiotarsus, left tarsometatarsus, and a proximal fragment of the right tarsometatarsus.

Other material belonging to Pterodroma zinorum : See Supporting Information, Table S1.

Suggested English name: Azorean Little Gadfly Petrel.

Suggested Portuguese name: Freira pequena dos Açores.

Diagnosis: A small species of Pterodroma similar in size to Pt. madeira from Madeira Island but with shorter forelimb bones (specially the ulna) and tarsometatarsus, but with a wider fossa glandulae nasalis in Pt. zinorum than in Pt. madeira . In addition, the distal extreme of the rostri maxillae of the new species shows a dorsal side higher and more curved than in Pt. madeira ( Fig. 2 View Figure 2 ).

Much smaller than the other Atlantic species of this genus ( Tables 2–4 View Table 2 View Table 3 ; Figs 2–7 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 ; Supporting Information, S1–S8), including the South Atlantic Pt. incerta (Schlegel, 1863) ( Carboneras et al. 2020a), but with a humerus longer than the small Pacific Ocean species of this genus, Pt. pycrossi Falla, 1933 , Pt. cookii (Gray, 1843) , Pt. leucoptera (Gould, 1844) , Pt. nigripennis (Rothschild, 1893) , and Pt. axillaris (Salvin, 1893) [see Table 3 View Table 3 and Cooper and Tennyson (2008)].

Remarks: The 14 C date of the complete right ulna of one specimen of Pt. zinorum sp. nov. from the type locality (RICH-21397) 1181 ± 30 BP was calibrated with 38 ± 139 (∆ R ± SD) providing the interval 1104–1672 CE ( Table 1 View Table 1 ). Although there is overlap in the length of the hindlimb bones (femur, tibiotarsus, and tarsometatarsus) of Pt. zinorum and Pt. madeira , forelimb bones referable to the former (humerus, ulna, and carpometacarpus) are smaller than in Pt. madeira ( Tables 2–4 View Table 2 View Table 3 ; Figs 2–4 View Figure 2 View Figure 3 View Figure 4 , 6 View Figure 6 , 7 View Figure 7 ; Supporting Information, Figs S1–S8), so Pt. zinorum is the smallest Atlantic species of the genus. The morphology of the postcranial bones of the new species is similar to that of Pt. madeira with differences in the bone length between the two species. The ulna, tarsometatarsus (Wilk’s Lambda = 0.203; d.f. = 4, 52; P <.001), and carpometacarpus (U = –2.683; P <.007, U = –2.761; P <.006) are smaller than Pt. madeira (tests performed between current bones of Pt. madeira and material from both Graciosa and Pico Islands, respectively). The new species has a shorter culmen (U = –2.121; P =.034) and a narrower nasofrontal joint (U = –2.236; P =.025) (tests performed between current bones of Pt. madeira and material from Pico) ( Tables 2–4 View Table 2 View Table 3 ; Fig. 2 View Figure 2 ).