Phylogenetic relationships of the extinct St Helena petrel, Pterodroma rupinarum Olson, 1975 (Procellariiformes: Procellariidae), based on ancient DNA

Palaeontological studies show that three endemic procellariid seabird species became extinct on the remote island of St Helena in the South Atlantic Ocean. At least one of these, Pterodroma rupinarum Olson, 1975, is likely to have survived until human colonization of the island, although it is known only from subfossil bones. Several species of Pterodroma are distributed across the Atlantic, but the skull and bill of Pt. rupinarum were judged to be more similar to the Indo-Pacific Pterodroma rostrata group, which was recently split into the separate genus Pseudobulweria. We used ancient DNA techniques to sequence the mitochondrial cytochrome b gene of the extinct Pt. rupinarum, and conducted phylogenetic analyses to investigate the placement of this enigmatic taxon. In trees constructed using maximum likelihood and Bayesian inference, Pt. rupinarum did not group with Pseudobulweria, but instead fell within a strongly supported clade of Atlantic Pterodroma, including the endangered Black-capped [Pterodroma hasitata (Kuhl, 1820)] and Bermuda [Pterodroma cahow (Nichols & Mowbray, 1916)] petrels, as well as the Macaronesian petrels [Pterodroma madeira Mathews, 1934, Pterodroma feae (Salvadori, 1899) and Pterodroma deserta Mathews, 1934]. Pterodroma rupinarum shared a particularly close relationship with Pt. feae of the Cape Verde Islands, which is also the geographically closest species within the clade. Considering the osteological distinctiveness of Pt. rupinarum it was probably a separate species, or at least a highly diverged population that was isolated for a substantial period of time prior to its extinction.