Ardenna buchananbrowni: A new species of diving Shearwater from the Pliocene of Taranaki, New Zealand.

Shearwaters, Procellariidae, are a diverse group of Tube-nosed Seabirds, Procellariiforms, with a fossil record going back to at least the Miocene (some Oligocene fossils have been assigned to the group - but the status of these is uncertain). All living and fossil Shearwaters are placed within three genera, the relatively large Calonectris, weighing 470–1060 g; the somewhat smaller Ardenna, weighing 320–950 g; and the notably smaller Puffinus, weighing 120–575 g (confusingly, Puffins are not Shearwaters at all, but members of the Auk family, Alcidae, with the generic name Fratercula). Shearwaters have a fairly good fossil record in the Northern Hemisphere, but until 2018 the known remains from the Southern Hemisphere comprised a few fragmentary bones from Mio-Pliocene assemblages in Chile, Peru, and South Africa. This changed with the discovery of Ardenna davealleni, a large gliding Shearwater from the Pliocene Taranaki Seabird Assemblage.

In a paper published in the journal Taxonomy on 6 April 2024, Alan Tennyson of the Museum of New Zealand Te Papa Tongarewa, Rodrigo Salvador of the Arctic University Museum of Norway, Barbara Tomotani of the Department of Arctic and Marine Biology at the Arctic University of Norway, and Felix Marx, also of the Museum of New Zealand Te Papa Tongarewa, describe a second Pliocene Shearwater from the Taranaki Assemblage.

The new species is described from two specimens. The first of these, NMNZ S.49931, is a partial articulated skeleton, comprising a complete skull and premaxilla, posterior right mandible, sternum, furcula, right coracoid, a row of articulated thoracic vertebrae, four ribs, both humeri, right ulna, right radius, and several small unidentified fragments, which was collected from Ohawe Beach, southern Taranaki, by Karl Raubenheimer. The second specimen, NMNZ S.49666, is another partial skeleton, comprising a complete skull and premaxilla, left quadrate, right coracoid, both humeri (missing their distal ends), right ulna, probable right radius, one vertebra, and several small unidentified fragments, collected by John Buchanan-Brown at Waihi Beach, South Taranaki. The species is placed in the genus Ardenna, and given the specific name buchananbrowni, in honour of John Buchanan-Brown.

Pliocene fossil Shearwater Ardenna buchananbrowni. (Top) Photograph of holotype NMNZ S.49931 and (bottom) explanatory line drawing. Tennyson et al. (2024).

Ardenna buchananbrowni is a small Shearwater, falling within the upper part of the size range of the genus Puffinus, and its general shape falls within the range of both Puffinus and diving members of the genus Ardenna. However, it is closest in form to Ardenna tenuirostris, the living Short-tailed Shearwater or Muttonbird, leading Tennyson et al. to conclude that it was a small diving member of the genus Ardenna.

Pliocene fossil shearwater Ardenna buchananbrowni, paratype NMNZ S.49666, with elements identified. Tennyson et al. (2024).

The genera Ardenna and Puffinus are calculated to have diverged about 10.4 million years ago, based upon molecular clock data, with members of the genus Puffinus becoming specialised in diving, and some members of the genus Ardenna also later becoming specialist divers, and converging in form with Puffinus. The Taranaki Seabird Assemblage has been dated to between 3.36 and 3.06 million years before the present, making Ardenna buchananbrowni the oldest known diving Ardenna as well as the smallest, and demonstrating that members of the genus had adapted to a diving lifestyle in the Southern Ocean more than 3 million years ago.

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Macronectes tinae: A new species of Giant Petrel from the Pliocene of Taranaki, New Zealand.

Giant Petrels, Macronectes spp., are the largest members of the Avian Family Procellariidae, and are easily identifiable by their large size, heavyset body, and distinctive bulbous beak. The genus currently comprises two species, the Southern Giant Petrel, Macronectes giganteus, found on Antarctica and the southern tips of Australia, Africa, and South America, and the Northern Giant Petrel, Macronectes halli, which ranges slightly further north, although there is a large overlap between the distributions of the two species. Bones assigned to the genus Macronectes have been uncovered in Pleistocene and Holocene deposits in New Zealand, although these are fragmentary, and have never been assigned to species level. 

In a paper published in the journal Taxonomy on 30 January 2023, Alan Tennyson of the Museum of New Zealand Te Papa Tongarewa and Rodrigo Salvador of the Department of Arctic and Marine Biology at the Arctic University of Norway, and the Arctic University Museum of Norway, describe a new species of Giant Petrel based upon  skull and a partial humerus from the Pliocene deposits of the Tangahoe Formation in the sedimentary Whanganui Basin in the western portion of New Zealand’s North Island.

The specimens were collected from beach boulders at South Taranaki, with the two specimens about 2 km apart, making it unlikely that they came from the same original Bird. Both were found by fossil collector Alastair Johnson, the skull in 2017 and the humerus in 2019, and are now housed in the collection of the Museum of New Zealand Te Papa Tongarewa. The new species is named Macronectes tinae, where 'tinae' honours Tina King, the late partner of Alastair Johnson; the fossil skull was her favorite fossil.

Skull (holotype, NMNZ S.048502) of Macronectes tinae, partially embedded in matrix, in different views; scale bar is 5 cm. (A) Dorsal view. (B) Lateral view (right). (C) Lateral view (left). (D) Anterior view. (E) Caudal view. Tennyson & Salvador (2023).

The large bulbous bill of the skull specimen, caused by a wider and enlarged corpus ossis premaxillaris and a deeper proximal premaxilla, leaves little doubt that it belongs in the genus Macronectes. However, this skull is distinctly smaller than that of either extant species assigned to the genus, which, combined with the Pliocene age of the fossil, is deemed sufficient by Tennyson and Salvador to justify the creation of a new species.

Only the shaft and distal end of the humerus are preserved, so that the main diagnostic feature of the genus Macronectes, a weakly developed second (dorsal) fossa pneumotricipitalis muscle attachment on the proximal end, cannot be observed. However, the bone does appear to come from a Fulmarine Procellariid Bird, and is to large to belong to any known member of that group other than a Giant Petrel, as well as being of an appropriate size for Macronectes tinae, as determined by the skull, leading Tennyson and Salvador to refer it to the species.

Detail of proximal end of the left humeri of selected Procellariiformes in cranial view; scale bar is 2 cm. (A) Antarctic Petrel, Thalassoica antarctica, NMNZ OR.018975. (B) Antarctic Fulmar, Fulmarus glacialoides, NMNZ OR.017595. (C) Southern Giant Petrel, Macronectes giganteus, NMNZ OR.029141. (D) Northern Giant Petrel, Macronectes halli, NMNZ OR.029173. (E) Macronectes tinae, paratype NMNZ S.048870. (F) Indian Yellow-nosed Albatross, Thalasarche carteri, NMNZ OR.02847. Tennyson & Salvador (2023).

Macronectes tinae is similar enough to modern Giant Petrels to be placed in the same genus with a high degree of confidence. It does, nevertheless, have some morphological variations, which would have had some functional differences in the living Bird, although, given the fragmentary nature of the specimen, it is difficult to asses what these would have been. It is, however, likely to have lived in a similar environment to modern Giant Petrels, which, unlike their closest relatives, are shorebirds rather than true pelagic ocean-dwellers, and unlike them capable of walking on land, where they are gregarious opportunistic scavengers and predators. The Tangahoe Formation in Taranaki is considered to represent a shore environment, with other fossils including colonial marine Mammals and a Penguin, making it likely that Macronectes tinae lived in similar environment to its modern relatives.

Artistic reconstruction of Macronectes tinae in its palaeoenvironment. A darker plumage was chosen for the reconstruction because a darker colouration in Giant Petrels seems to be related to warmer regions, as Taranaki had warmer temperatures during the Pliocene. Simone Giovanardi in Tennyson & Salvador (2023).

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