Sphenisciformes

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Sphenisciformes (Sharpe 1899), an order of class Aves, commonly known as penguins.

Alfred Newton, that most ascerbic of critics in the early history of modern ornithology, noted of the penguins,

"There is perhaps scarcely a feather or a bone which is not diagnostic...The title of an Order can scarcely be refused to the Impennes"

Newton's comments underscore the singular oddity of these Antarctic birds. Without a question, penguins are more highly adapted for wing-propelled diving than any other birds known. There are seventeen living species of penguins in six genera, all are flightless and limited in distribution to the southern oceans, save for the Galapagos Penguin.

Due to their peculiar anatomy, the origin of penguins and their subsequent evolution have long been debated, focusing on two pivotal questions: were the ancestors of penguins volant or flightless, and to which if any extant order are penguins most closely related? Early attempts to map the phylogenetic relationships of penguins to other neornithine birds largely grouped them with other aquatic forms, e.g., Gray (1849), placed penguins within his "Anseres", which bracketed all swimming birds in a clearly polyphyletic hodge-podge taxon. Huxley (1867) grouped penguins with other schizognathous birds within his diffuse "Spheniscomorphae" and noted similarities, largely superficial, with auks (Alcidae) and in particular the famed Great Auk, Alca (=Pinguinis) impennis. Both Garrod (1873d, 1874a) and Sclater (1880b) argued that penguins were closely allied with loons and grebes. Watson (1883) could find no convincing evidence for any close affiliation with other avian orders and concluded that penguins represent an ancient radiation so modified to meet their aquatic habitus that resolving the origin of the group was intractable.

Later, Stejneger (1885) concurred with this assessment and stressing the differences between penguins and all other birds, elevated them to a superorder, Impennes. Menzbier (1887) proposed that penguins were derived from a reptilian ancestor distinct from that of other birds, a viewpoint later argued in more explicit detail by Lowe (1933a, 1939a). It was Furbringer (1888) who first argued compellingly for the procellariid affinities of penguins (though he did not regard them as sister groups), and he dismissed alleged similarities between grebes, loons and penguins as convergent. Gadow (1893) furthered this assessment and argued that the procellariids were the closest living relatives of the penguins. Pycraft (1898c) concurred with this postulate.

Despite the perspicacity of their forebears, later systematists indulged all manner of curious and generally unsubstantiated hypotheses regarding penguin origins. Beddard (1898a) argued that penguins were related to the Hesperornithiformes, a hypothesis repeated by Chandler (1916). Lowe (1933a, 1939a), in one of the most notorious arguments in his generally contentious career, argued that penguins were derived from reptilian ancestors distinct from that of all other carinates, and that their immediate ancestors, were flightless. Simpson (1946) thoroughly dismantled Lowe's idiosynchratic argument and it has become a memorable if very incorrect footnote in the history of penguin classification.

Indeed it was with Simpson's 1946 work, synthesizing data gathered from earlier sources (e.g., Murphy & Harper 1921, Murphy 1936), that a truly coherent scenario for the evolution of penguins and defense of a particular hypothesis for the origin thereof appeared. Simpson (1946) maintained that penguins were most closely allied with the procellariids, and felt that aerial oceanic birds moving through adaptive intermediate stages, gave rise to the specialized underwater-diving behavior seen in penguins. Howard (1950) and Mayr & Amadon (1951) both concurred with Simpson's hypothesis. Kinsky (1960) found similarities in the morphology of the nostrils of Eudyptula minor and procellariids and argued that these data further indicated a procellariid affinity for penguins.

Simonetta (1963), resurrected the idea of gaviiform/podicipediform relationships for penguins in a study cranial kinesis and morphology, with which Olson (1985a) agreed on the basis of fossil evidence. Sibley & Ahlquist (1972) argued on the basis of electrophoretic patterns of egg-white proteins that penguins were more closely related to procellariid birds than any other extant neornithines. Their DNA-DNA hybridization study (Sibley & Ahlquist 1990), concurred with this hypothesis.

Given the abundance of data, both morphological and molecular to suggest that penguins are more closely related to Procellariiformes (Procellarioidea of Sibley & Ahlquist 1990), alternative suggestions for a sister group relationship with other avian orders (e.g., Gaviiformes) must be viewed with skepticism.

Penguins are among the most ancient of birds, with a fossil record extending back to the Upper Eocene (Olson 1985a, Feduccia 1996). Penguins reached gigantic proportions in the Miocene, with some genera producing species nearly two meters tall (e.g., Pachydyptes, Anthropornis).

References

1. Beddard, F. E. 1898a. The structure and classification of birds. Longmans, Green & Co., London.
2. Chandler, A. C. 1916. A study of the structure of feathers, with reference to their taxonomic significance. University of California Publications in Zoology 13: 243-446.
3. Feduccia, A. 1996. The Origin and Evolution of Birds, First Edition. Yale University Press, new Haven.
4. Furbringer, M. 1888. Untersuchungen zur Morphologie und Systematik der Vogel. Vols. 1, 2. 1751 pp. Von Holkema, Amsterdam.
5. Gadow, M. 1893. Vogel. II. Systematischer Theil. In: Bronn's Klassen und Ordnungen des Thier-Reichs, vol. 6(4). C. F. Winter, Leipzig.
6. Garrod, A. H. 1873d. On certain muscles of the thigh of birds and on their value in classification. Part I. Proceedings of the Zoological Society of London 1873: 626-644.
7. Garrod, A. H. 1874a. On certain muscles of birds and their value in classification. Part II. Proceedings of the Zoological Society of London 1874: 111-124.
8. Gray, G. R. 1844-49. The genera of birds. 3 vols. R. & J. Taylor, London.
9. Howard, H. 1950. Fossil evidence of avian evolution. Ibis 92: 1-21.
10. Huxley, T. H. 1867. On the classification of birds; and on the taxonomic value of the modifications of certain of the cranial bones observable in that class. Proceedings of the Zoological Society of London 1867: 415-472.
11. Kinsky, F. C. 1960. The yearly cycle of the northern blue penguin (Eudyptula minor novahollanddiae) in the Wellington harbour area. Dominion Museum (New Zealand) Record 3: 145-218.
12. Lowe, P. 1933a. On the primitive characters of penguins, and their bearing on the phylogeny of birds. Proceedings of the Zoological Society of London 1933: 483-541.
13. Lowe, P. 1939a. Some additional notes on Miocene penguins in relation to their origin and systematics. Ibis 81: 281-296.
14. Mayr, E. & Amadon, D. 1951. A classification of Recent birds. American Museum Novitates 1496: 1-42.
15. Menzbier, M. von. 1887. Vergleichende Osteologie der Pinguine in Anwendung zur Haupteintheilung der Vogel. Bull. soc. Imp. natur. Mouscou 483-587.
16. Murphy, R. C. 1936. Oceanic birds of South America. American Museum of Natural History, New York. 2 vols.
17. Murphy, R. C. & Harper, F. 1921. A review of the diving petrels. Bulletins of the American Museum of Natural History 44: 495-553.
18. Olson, S. L. 1985a. The fossil record of birds. In: Farner, D. S., King, J. R., & Parkes, K. C., Avian Biology, vol. 8, 79-252.
19. Pycraft, W. P. 1898c. Contributions to the osteology of birds. Part II. Impennes. Proceedings of the Zoological Society of London 1898(1899): 958-989.
20. Sclater, P. L. 1880b. Remarks on the present state of the systema avium. Ibis 22: 340-350, 399-411.
21. Sharpe, R. B. 1899. A hand-list of the genera and sepcies of birds. Vol. 1. British Museum, London.
22. Sibley, C. G. & Ahlquist, J. E. 1972. A comparative study of the egg-white proteins of non-passerine birds. Bulletin of the Peabody Museum of Natural History, Yale University 39: 1-276.
23. Sibley, C. G. & Ahlquist, J. E. 1990. Phylogeny and Classification of Birds: A Study in Molecular Evolution. Yale University Press, New Haven.
24. Simonetta, A. M. 1963. Cinesi e morfologia del cranio negli ucceli non-passeriformi: studio su varie tendenze evolutive. Part II. Striges, Caprimulgiformes ed Apodiformes. Archivo Zoologico Italiano (Turin) 53: 1-36.
25. Simpson, G. G. 1946. Fossil penguins. Bulletin of the American Museum of Natural History 87: 1-100.
26. Stejneger, L. 1885. Birds. In: Kingsley, J. S. (ed.), The Standard Natural History, vol. 4. S. E. Cassino, Boston.
27. Watson, M. 1883. Report on the anatomy of the Spheniscidae collected during the voyage of H.M.S. Challenger. In: Great Britain and Ireland, Challenger Office: Report on the scientific results of the voyage of H.M.S. Challenger 1873-1876, Zool. 7(18): 244 pp.