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First fossil bird from East Antarctica

Jeffrey D. Stilwell, Department of Geology, University of Nebraska, Lincoln, Nebraska 68588-0340

Craig M. Jones, Department of Geology, University of Canterbury, Christchurch, New Zealand

Richard H. Levy and David M. Harwood, Department of Geology, University of Nebraska, Lincoln, Nebraska 68588-0340

Remains of a large fossil bird (Aves) of Middle Eocene age were discovered by University of Nebraska-Lincoln geologists during the 1995-1996 austral season. This is the first record of a fossil bird from East Antarctica. The fossil was collected in glacial moraine deposits flanking the upper northwestern side of Mount Discovery in McMurdo Sound (figure 1). New data gleaned from the bone will help bridge a major gap in our scant knowledge of Paleogene vertebrates of Antarctica. The recovery of Aves remains (often fragile and hard to preserve) indicates the potential presence of other vertebrate remains in the McMurdo Sound erratics.

The only information hitherto available on Eocene antarctic Aves has been those of penguins (Spheniscidae), rather common in the extensive, highly fossiliferous deposits of the La Meseta Formation of Seymour Island on the northeastern tip of Antarctic Peninsula, and other fossil birds recorded from Seymour Island since 1980 including those of the Pelagornithidae, Diomedeidae, Phororhacidae?, and a probable ratite (see Seymour Island papers and comments on fossil birds by Wiman 1905; Marples 1953; Simpson 1971; Tonni 1980; Tonni and Tambussi 1985; Case, Woodburne, and Chaney 1987; Tambussi and Tonni 1988; Fordyce and Jones 1990; Myrcha, Tatur, and del Valle 1990; Stilwell and Zinsmeister 1992; Tambussi et al. 1994).

Figure 1. Location map of fossil pseudodontorn bird locality, Mount Discovery, McMurdo Sound, East Antarctica. (Km denotes kilometer.)

Also known from Seymour Island is a loonlike bird (Chatterjee 1989), which is of latest Cretaceous age, was collected from the Lopez de Bertodano Formation, and is possibly referable to the fossil loon Neogaeornis wetzeli (Aves: Gaviidae) (Olson 1992). The remains of a latest Cretaceous shorebird (Anseriformes: Presbyornithidae) were discovered recently in the Lopez de Bertodano Formation of Vega Island, Antarctic Peninsula (Noriega 1995). The Seymour and Vega islands fossils represent the oldest fossil birds from Antarctica. The only other record of fossil birds from Antarctica, albeit indirect evidence, is of bird tracks of Tertiary age from Fildes Peninsula of King George Island, South Shetland Islands (Covacevich and Rich 1982).

The erratic containing the bird bone from Mount Discovery is a fossiliferous, medium-grained sandstone interpreted to have been deposited in a shallow marine environment. The bone, a probable humeral shaft (figure 2), is abraded and moderately crushed, suggesting that it was exposed on the seafloor for some time before burial. Whether the bone was crushed during a predator attack or by postmortem taphonomic processes is uncertain, because only a fragment of the bone is preserved. The fragment is approximately 95 millimeters (mm) long with a maximum diameter of 33 mm. The bone is straight and hollow and has thin walls (2-3 mm) relative to its size. The proximal? end is exposed on the surface of the erratic and has an inflated, approximately triangular cross-section. A wide, shallow groove runs along one face of the bone; it is deepest at the proximal? end. The remainder of the bone is badly crushed and abraded, and it lacks any other positively identifiable features. The size of the bone indicates that the bird, when alive, was quite large. The hollow nature of the bone precludes placement of the bone in Spheniscidae. The thin walls, large size, and straightness of the fragment indicate it is probably a humeral shaft fragment from a longbone of a large volant (flying) bird, the most likely candidate being a pseudodontorn ("false-toothed" bird) belonging to the Pelecaniformes: Odontopterygia: Pelagornithidae.

Figure 2. Two views of the humeral shaft bone of Middle Eocene pseudodontorn bird from Erratic E303, Mount Discovery; length of bone is approximately 95 mm.

The pseudodontorns (sensu Olson 1985) (see figure 3) are a highly specialized group of extinct seabirds, related to cormorants, gannets, boobies, pelicans, tropic birds, and frigatebirds (Pelecaniformes). They are characterized by their large size; robust bill, which had numerous toothlike bony projections developed along its edge; elongate, thin wing bones; and humeral head morphology that reduced mobility in the shoulder joint. Olson (1985) suggested that the pseudodontorns were similar to extant albatrosses in that they were predominantly pelagic? or marine gliders.

Figure 3. Reconstruction of a pseudodontorn bird in the Middle Eocene east antarctic coastal environment. Note araucarian and southern beech tree (Nothofagus) forest, based on fossil leaf and wood material associated with the bone and similar erratics.

Pseudodontorns have a fossil record ranging from Early Eocene to Pliocene. They are known from marine deposits in Great Britain, Europe, North America (Atlantic and Pacific coasts), Japan, Africa, New Zealand, and Antarctica. The pseudodontorn record from Antarctica is derived from the Middle Eocene to ?lowermost Oligocene sediments of the La Meseta Formation on Seymour Island, Antarctic Peninsula (Tonni 1980; Tonni and Tambussi 1985; Stilwell and Zinsmeister 1992; and personal observation in 1994, R. Ewan Fordyce collection of University of Otago Geology Department, New Zealand). Unfortunately, the Seymour Island material, comparable to the Mount Discovery specimen, is fragmentary and is not identifiable at genus- and species-level. Nevertheless, the antarctic records of these fossil birds are among the oldest known, representing the near base of the radiation of the group.

The age of the bird bone is based on associated mollusks, decapods, and microfossils (dinoflagellates). A moderately well-preserved turritellid gastropod specimen associated with the bone, identified as probably conspecific with Colposigma euthenia Stilwell and Zinsmeister of Seymour and Cockburn islands, indicates an Eocene age. On Seymour Island, Colposigma euthenia ranges from unit I to unit VI in the La Meseta Formation, indicating a late Early to mid-Late? Eocene age. A probable fragment of the venerid bivalve Eurhomalea sp. also supports an Eocene age, as does a small fragment of the decapod Callichirus? symmetrica (Feldmann and Zinsmeister), which was dated recently as late Early to Middle Eocene age (Stilwell et al. in press). Other macrofossils that are present with the bones but are not age diagnostic include plant fragments and other unidentifiable fossil fragments. Dinoflagellate taxa associated with the bone include Deflandrea antarctica Wilson, Senagalinium? asymmetricum (Wilson), Spinidinium macmurdoense (Wilson), Vozzhennikovia apertura (Wilson), Enneadocysta partridgei Stover and Williams, Lejeunecysta hyalina (Gerlach), and Hystrichosphaeridium truswelliae Wrenn and Hart. The antarctic age constraints for these dinoflagellate taxa are currently under study by Richard H. Levy but suggest a Middle to Late Eocene age for the bird bone. The pseudodontorn material from the La Meseta Formation of Seymour Island was collected from the middle units of the formation, indicating a Middle Eocene age (Askin personal communication), thus strengthening the probability that the Mount Discovery specimen is coeval.

This find of a probable pseudodontorn at Mount Discovery is significant not only because these birds were a widespread, important component of the Eocene high-latitude avifauna but also because the find indicates an apparent link between east and west antarctic faunal elements.

We wish to thank the personnel of McMurdo Station, Ross Island, including the VXE-6 Squadron, for supporting our research in Antarctica. John Kaser, University of Nebraska-Lincoln, discovered the erratic containing the bird bone, and we thank him for finding it in a sea of erratics in the Mount Discovery moraine. Steve Bohaty, University of Nebraska-Lincoln, assisted in the field, and we thank him for his enthusiasm for collecting fossils. This research was supported by the Alumni of the Department of Geology, University of Nebraska-Lincoln, and National Science Foundation grants OPP 93-17901 and OPP 91-58075 to Harwood.


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