Phoeniconotius eyrensis

Introduction

Phoeniconotius eyrensis, from the late Oligocene of South Australia, was one of the most massively built flamingos known. At the time Lake Eyre was a vast inland lake, home to many other water birds as well as crocodiles, lungfish and numerous marsupials. The youngest Australian fossil flamingo is Pleistocene in age. Flamingos most likely became extinct in Australia as increasing aridity caused permanent inland waterways to disappear.

Identification

Flamingos are generally put into their own order, Phoenicopteriformes. Flamingos have waterproof plumage, long necks and legs (the legs being longer than the body), webbed feet, and a goose-like call.

The monotypic Phoeniconotius eyrensis was one of the largest and most massively built flamingos known. It was more robust than either its contemporary at Lake Eyre, Phoenicopteris novaehollandiae, or the living Greater Flamingo, Phoenicopteris ruber. Phoeniconotius is known only from a left distal tarsometatarsus with one associated phalange (toe bone), and a second phalange from the opposite foot. Phoeniconotius is identified as a true flamingo because it shares features of the trochlear articulation only with other flamingos (trochlea II is elevated and deflected strongly towards the plantar surface of the foot; and the posterior spur of trochlea II is narrow and sharply offset from the articular surface). Phoeniconotius resembles species of Phoenicopteris, but there are anatomical differences in the trochlear articular surfaces. Judging from the estimated size of its feet, Phoeniconotius was a bit larger than Phoenicopteris ruber. However, the relative length of its legs is unknown. It is comparable in size to the Miocene Megapaloelodus from South Dakota.

The articular surface of the bottom of the foot (plantar surface) is less extended in Phoeniconotius than in species of Phoenicopteris, suggesting that Phoeniconotius was not as good a swimmer as Phoenicopteris (i.e., not a deep water wader or swimmer but possibly a shallow water wader and more terrestrial in its habits). Digit III was comparatively short and stout in Phoeniconotius, further evidence that it was not a strong swimmer. Its hind toe (digit 1) was strongly built (the articulation for metatarsal I is well developed and broad), a feature shared with Phoenicopteris novaehollandiae, A well developed hind toe and articulation is an archaic character also seen in Paloelodus, cranes, storks and ibises.

Habitat

Lake Eyre during the late Oligocene-early Miocene was a vast, shallow, permanent saline/alkaline lake. It was home to many species of water birds, lungfish, fish, turtles and crocodiles. Varanid lizards and various marsupials (including kangaroos, diprotodontoids and marsupial 'lions', or thylacoleonids) lived along its shores.

Distribution

Phoeniconotius eyrensis comes from east of Lake Eyre, South Australia.

Feeding and diet

Flamingos feed on crustaceans, molluscs, insect larvae and adults, small fishes, algae and diatoms. Small aquatic crustaceans and other aquatic invertebrates with alpha and beta carotenoid pigments give the flamingo's feathers their characteristic pink colour. The bill shape of a flamingo determines its diet. Deep-keeled flamingos feed on tiny diatoms and algae while flamingos with shallow-keeled bills feed on larger food items (insects and other small invertebrates). The relationships of Phoeniconotius are unknown, and there is no skull or beak preserved, so its feeding method must remain conjectural. However, differences in feeding habits allow more than one species of living flamingo to co-exist, which may explain the co-occurrence of two flamingo species at Lake Eyre during the Oligocene.

Life history cycle

Flamingos are social birds and usually nest in huge colonies. Breeding usually occurs once a year, and hatching of chicks is synchronized. Flamingos usually don't breed until about the age of six although their longevity in the wild is unknown. Flamingos are not migratory birds, and depend on permanent water bodies for nesting and feeding. In spite of the protection of a large colony in a remote location, young may be taken by predators, mainly other birds (for instance, hawks and storks).

Two species of flamingos were contemporaneous at Lake Eyre during the late Oligocene, Phoeniconotius eyrensis and Phoenicopteris novaehollandiae. Co-existence by more than one species of flamingo is not uncommon, and is also seen in the Pliocene of Australia at Lake Kanunka (also near Lake Eyre) where three flamingo species lived together. Living species of flamingos often congregate together (as in the high altitude playa lakes of Chile), and this is also recorded from the fossil record (e.g., from the Oligocene of France).

Fossils description

Flamingo fossils are often well preserved, since their habitat - vast, shallow, alkaline or saline lakes - is ideal for fossilization. It is often the sturdy ends of the long limb bones that are found. Phoeniconotius eyrensis comes from the Ngapakaldi Local Fauna (Lake Pitikanta), Etadunna Formation, Lake Eyre, South Australia. The holotype (the distal end of a left tarsometatarsus, with the proximal phalanx of left digit III and proximal phalanx of right digit IV) is held by the University of California Museum of Paleontology.

Evolutionary relationships

Flamingos are an ancient family of birds (Phoenicopteridae), and have not changed much since the Oligocene (particularly in the structure of the feet and legs). The oldest flamingo fossils are Eocene in age (about 50 million years old), and are more archaic than more modern species, which had appeared by the early Oligocene (about 30 million years ago). The phylogenetic relationships of flamingos are unresolved; they are anatomically most like storks, but their behaviour is more like that of other water birds such as geese. Living flamingos are restricted to the tropics or subtropics and are found in the Caribbean, North and South America, Africa, India and Europe (including the Mediterranean).

Australian fossil flamingos, known from the middle Cainozoic to the Pleistocene, were surprisingly diverse (six species in four genera, a level of diversity equal to or greater than in many parts of the world where flamingos now occur). Their relationships are difficult to determine because of the fragmentary nature of the fossils. To compound the problem, Australian fossil flamingos were originally described as storks, waders or ibises (De Vis, 1906). Alden Miller, who described Phoeniconotius (Miller 1963a), therefore did not consult these misidentified specimens, leading to some confusion in the literature.

Fossil flamingos are known from many central Australian Miocene fossil sites (Lake Palankarinna and Lake Pinpa in South Australia; and Bullock Creek and Alcoota in the Northern Territory). They are also known from Pliocene sites in Queensland (Bluff Downs); and from the Pleistocene of South Australia (Cooper Creek). Early Pliocene fossils are relatively common, but by the late Pleistocene flamingos have almost disappeared, with just a few bones collected from the poorly dated Cooper Creek sediments. Most Australian species and genera were unique to Australia, although the living Greater Flamingo, Phoenicopteris ruber, is known from the Pliocene of South Australia . Phoeniconotius was an endemic, monotypic Australian genus. Its large hind toe may be an ancestral feature, since it has been reduced in more advanced flamingos. Although it may have been a shallow water wader and possibly more terrestrial than most flamingos, its foot morphology and massive build does not suggest a relationship with Paloelodus, which was also stoutly built and possibly more terrestrial than other flamingos. This unusual morphology suggests that Phoeniconotius may represent a separate branch of Phoenicopteridae.

The gradual disappearance of permanent water bodies, particularly large lake systems like Lake Eyre, are the probable reason for the disappearance of flamingos from Australia. Flamingos live in huge colonies and normally do not migrate, and require reliability and permanence in their breeding and feeding grounds. Flamingos held on in a progressively drier Australia until the late Pleistocene, when the climate deteriorated and the last of the large lake systems became ephemeral rather than permanent.

References

• Boles, W. E. 2006. Chapter 21: The avian fossil record of Australia: an overview. Pp. 387-411 in Merrick, J. R., Archer, M., Hickey, G. M. and Lee, M. S. Y. (eds) Evolution and Biogeography of Australasian Vertebrates. Australian Scientific Publishing, Oatlands.
• De Vis, C. W. 1906. A contribution to the knowledge of the extinct avifauna of Australia. Annals of the Queensland Museum 6, 1-25; plates 1-9.
• Miller, A. H. 1963a. The fossil flamingos of Australia. Condor 65, 289-299.
• Milne-Edwards, A. 1867-1871. Recherches anatomiques et paléontologiques pour servir a l'histoire des oiseaux fossils de la France. Vol. 2; atlas, Vol. 1. G. Masson, Paris.
• Stirton, R., Tedford, R. and Mills, A. H. 1961. Cenozoic stratigraphy and vertebrate paleontology of the Tirari Desert, South Australia. Records of the South Australian Museum 14, 19-61.
• Vickers-Rich, P. 1991. Chapter 20: the Mesozoic and Tertiary history of birds on the Australian Plate. Pp. 721-808 in Vickers-Rich, P., Monaghan, J. M., Baird, R. F. and Rich, T. H. (eds) Vertebrate Palaeontology of Australasia. Pioneer Design Studio, Melbourne.

Further reading

• Gould, S. J. 1985. The Flamingo's Smile: Reflections in Natural History. W. W. Norton & Company, Inc., New York.
• McMillan, B. 1997. Wild Flamingos. Houghton Mifflin, Boston.