Procellaria altirostris, Tennyson & Tomotani, 2021

Procellaria altirostris sp. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:093F56E5-D07E-44C3-8E75-059C486CB222

Etymology: From the unusually deep premaxilla in comparison to other members of the Procellaria genus.

Holotype: NMNZ S.46691; partial skeleton embedded, but largely exposed,in a concretion.Elements preserved: partial cranium (crushed) with premaxilla, furcula, both coracoids, right scapula, right humerus, both ulnae, right radius, synsacrum, left femur, both tibiotarsi, both tarsometatarsi but the left is missing both ends, one pedal phalange, and other fragments . The fossil is from a fully grown individual based on bone ossification ( Fig. 2 View Figure 2 ).

Type Locality, Type Horizon and Age: Ohawe Beach, south Taranaki, North Island , New Zealand ( New Zealand Fossil Record Electronic Database Number Q21/F0175, Fig. 3 View Figure 3 ). The fossil was found inside a marine mudstone concretion loose on the beach in 2015, and prepared by John Buchanan-Brown in the same year. The concretion is presumed to have eroded from an adjacent cliff in the Tangahoe Formation. This Formation is 3.0-3.4 Ma (local Waipipian stage, late Pliocene, Piacenzian; McKee, 1994; Naish et al., 2005; Thomas et al., 2020). Such concretions are thought to have formed on the ocean floor at a depth of up to 50 m or more ( Tennyson & Mannering, 2018).

Generic attribution: Procellaria altirostris sp. nov. is referred to Procellaria because it is a large petrel falling in the size range of Procellaria species and outside the size range of every other recent genus in Procellariiformes : all recent Diomedeidae are larger and all Hydrobatidae and Pelecanoididae are smaller. Within the family Procellaridae , birds in the Procellaria genus are the largest, with the exception of Macronectes Richmond, 1905 , which is similar in size to some albatross taxa. Based on the narrow and deep beak, the strongly hooked premaxilla and the prominent pila supranasalis, the genus Procellaria can be easily distinguished from almost all other genera within the Procellaridae ; the exceptions being Pterodroma Bonaparte, 1856 and Pseudobulweria Mathews, 1936. Generally, Pterodroma taxa have a narrower and shorter beak than Procellaria taxa; moreover, as in all Procellaria , the fossil has a longer humerus than ulna, while Pterodroma taxa have longer ulnae than humeri ( Tennyson & Mannering, 2018). The apertura nasi ossea of Pseudobulweria is smaller than in Procellaria taxa; moreover, the proximal end of the humerus of Pseudobulweria taxa lack the tubercle on the cranial surface of the ventral margin in the bicipital area (Tennyson & Mannering, 2018).The shape of the apertura nasi ossea and this humeral tubercle of the fossil are features found in Procellaria taxa ( Tennyson & Mannering, 2018).

Differential diagnosis: Procellaria altirostris sp. nov. is identified as a member of the Procellariiformes by the beak having a sharply hooked tip, lateral furrows rostral of the nostrils (nasolabial grooves) and marked supraorbital fossae for nasal glands (fossa glandulae nasalis), i.e., salt glands.

Procellaria altirostris sp. nov. is most similar to the White-Chinned Petrel ( P. aequinoctialis ), Spectacled Petrel ( P. conspicillata ) and Westland Petrel ( P. westlandica ). Compared with these taxa, the new species has a deeper and shorter premaxilla, a larger coracoid and shorter wings, while its legs are a similar size. It is slightly larger than the Grey Petrel ( P. cinerea ) and notably larger than the Black Petrel ( P. parkinsoni ). The Grey Petrel also differs in having a more slender beak (width and depth relative to length) than all other members of the genus. Procellaria species show minor sexual dimorphism in size, with males averaging a little larger (Marchant & Higgins, 1990; Warham, 1990). However, regardless of the sex of the fossil, it still falls outside the range of variation seen in other species ( Table 1 View Table 1 , Fig. 2 View Figure 2 , Fig. 4 View Figure 4 , Appendix 2).

Measurements: see Table 1 View Table 1 , Fig. 1 View Figure 1 .

Distribution: The holotype is the only known specimen of Procellaria altirostris sp. nov. All members of the genus Procellaria travel thousands of kilometres at sea when foraging and/or migrating ( Brooke, 2004), so we expect that Procellaria altirostris sp. nov. had similar behaviours and would have ranged widely in the seas around proto – New Zealand and probably been a long-distance migrant like other members of this genus ( Brooke, 2004).

DISCUSSION

The discovery of a well-preserved specimen of a Procellaria petrel from the Pliocene adds important new knowledge about the history of this genus. Only two previous studies have identified this genus in Pliocene deposits and those were disarticulated remains: a single partial humerus from the early Pliocene of South Africa ( Olson,1985a) and three bones from the early Pliocene of North Carolina, USA ( Olson & Rasmussen, 2001). No older fossils of the genus are known ( Olson, 1985b). Otherwise only much younger (Holocene) fossils have been documented (e.g., Tennyson, 2020; Worthy & Jouventin, 1999).

This lack of a good fossil record for the genus has impaired more detailed analyses of its evolution.Our description of a Pliocene Procellaria provides further evidence to support the phylogeny proposed by Penhallurick & Wink (2004), which suggested that crown-group Procellaria taxa were already present in the Miocene.

While we can only speculate on the functional significance of the minor skeletal differences between P. altirostris sp. nov. and other members of the genus, the fossil species probably had similar feeding strategies to living Procellaria . For example, surface feeding and shallow diving, with a diet consisting mainly of fishes, cephalopods and crustaceans ( Brooke, 2004). When compared with other Procellaria , the relatively short wings, particularly the short ulna compared with the humerus length, suggest that it may have been less of a glider ( Kuroda, 1955), perhaps using diving more often as a feeding strategy.

Finally, while New Zealand today is the worldwide centre of diversity for species of procellariiforms, including Procellaria ( Dickinson & Remsen, 2013) , the new Pliocene fossil is the only evidence of Procellaria petrels being present in the country prior to the Late Pleistocene ( Gill et al., 2010) and demonstrates a longer history for the genus in the region.