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7 June 2017 Oligocene and Miocene albatross fossils from Washington State (USA) and the evolutionary history of North Pacific Diomedeidae
Gerald Mayr, James L. Goedert
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Abstract

Albatross fossils have been collected from the late Oligocene Lincoln Creek Formation and the early/middle Miocene Astoria Formation near the townsite of Knappton, Pacific County, Washington (USA). The albatross from the Lincoln Creek Formation, Diomedavus knapptonensis, n. gen. et sp., is smaller than all extant albatrosses and represents the oldest published fossil albatross from the North Pacific Basin. Diomedavus knapptonensis is clearly distinguished from extant albatrosses in several osteological features; some are likely plesiomorphic, supporting a phylogenetic position outside the crown group. The unusual shape of the deltopectoral crest of the humerus suggests that D. knapptonensis also differed from extant albatrosses in its flight performance. A partial skeleton from the Astoria Formation likely represents another new albatross species; however, it is not named because there is no overlap with the skeletal elements of other fossil Diomedeidae. This species, here informally termed the “Astoria Formation albatross,” also identified as a stem group representative of the Diomedeidae, differs from extant species in subtle features of the leg bones. Therefore, stem group albatrosses inhabited the North Pacific Basin before the emergence of the taxon Phoebastria, which includes extant North Pacific albatrosses. Cenozoic albatrosses were widely distributed in the Northern Hemisphere and the complex biogeographic history of the Diomedeidae may have been shaped by changes in global marine or atmospheric circulation systems and the loss of safe breeding grounds.

INTRODUCTION

Albatrosses (Diomedeidae) were long split into the taxa Phoebetria (sooty albatrosses) and Diomedea (all others; e.g., Carboneras 1992); however, analyses of mitochondrial sequence data showed that Phoebetria is nested within the extant species and Diomedea as traditionally recognized is therefore paraphyletic (Nunn et al. 1996, Chambers et al. 2009). Accordingly, albatrosses are now classified in the 4 taxa Phoebetria, Phoebastria (North Pacific albatrosses), Thalassarche (southern mollymawks), and Diomedea (great albatrosses). Although most species of these taxa inhabit the Southern Hemisphere, 3 of the 4 species of Phoebastria breed in the North Pacific Basin.

The distribution of the extant species suggests that albatrosses evolved in the Southern Hemisphere, with a later dispersal of the Phoebastria lineage to the Northern Hemisphere. The evolutionary and biogeographic history of albatrosses is, however, poorly understood (Olson 1985a, Mayr 2016a) and few fossils have been described from strata predating the Pliocene, the epoch that began 5.3 million years ago (mya).

Fragmentary remains of putative Diomedeidae were reported from middle Eocene (∼39–41 mya) marine sediments in Uzbekistan (Murunkus; Panteleyev and Nessov 1987) and from late Eocene (∼38 mya) strata in Antarctica (Notoleptos; Acosta Hospitaleche and Gelfo 2016; a coracoid of a putative loon described by Acosta Hospitaleche and Gelfo 2015: figure 3A is here considered to be from a closely related procellariiform bird). These Eocene fossils are from very small species and, if correctly identified, clearly represent stem group albatrosses (Murunkus subitus measured only one-third the size of the extant Thalassarche melanophris and with an estimated tarsometatarsus length of 45–50 mm, Notoleptos giglii reached about 55–60% the size of Th. melanophris). A much larger stem group representative of the Diomedeidae was also reported from early Oligocene (∼32–34 mya) rocks in Belgium (Mayr and Smith 2012a). This species, Tydea septentrionalis, was of similar size to Th. melanophris, but clearly differed from crown group Diomedeidae in plesiomorphic features.

Two species of the taxon Plotornis, P. delfortrii and P. graculoides, were described from the early Miocene (∼20–23 mya) of France and Italy, respectively, where albatrosses no longer live (Cheneval 1984, Mayr and Pavia 2014). The smaller size and less well developed processus supracondylaris dorsalis on the distal humerus indicate that Plotornis is also a stem group representative of the Diomedeidae. Otherwise, however, the preserved bones of Plotornis species are very similar to those of extant albatrosses and certainly these early Miocene species are more closely related to the crown group than are the geologically older taxa Murunkus, Notoleptos, and Tydea.

The fossil record of modern-type albatrosses is restricted to the Neogene period (Miocene and younger) and most of the published material consists of very fragmentary remains, therefore we use quotation marks here to denote uncertainty regarding the generic assignment. “Diomedeatanakai from late early Miocene (16.5–17.5 mya) strata in Japan is based on tarsometatarsi and a beak fragment (Davis 2003). A pedal phalanx of an undetermined albatross species of late Miocene age was reported from Argentina (Olson 1984; erroneously considered to be of early Miocene age by Mayr and Smith 2012a) and a late Miocene species from Australia (“Diomedeathyridata) is based on a partial beak (Wilkinson 1969). All other Miocene albatross fossils, however, stem from North America.

Diomedeacalifornica from middle Miocene rocks in California is represented by a partial tarsometatarsus, a second referred tarsometatarsus, a referred distal humerus, and a tentatively referred distal tibiotarsus (Miller 1962; Howard 1966, 1978). Even more incompletely known is “Diomedeamilleri of middle Miocene age from California, the holotype of which is the proximal end of an ulna (Howard 1966) as well as a referred fragmentary proximal end of a tarsometatarsus (later designated as the “paratype”; Howard 1972). Fragmentary albatross remains of unnamed species were also found in various late Miocene localities in California (Miller 1935; Howard 1978, 1982).