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A Production of

Spheniscus demersus, Jackass Penguin
Dr. Nina Triche - The University of Texas at Austin
Spheniscus demersus
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skull
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Florida Museum of Natural History (UF 21341)

Image processing: Dr. Jessie Maisano
Publication Date: 11 Oct 2005

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The jackass penguin (Spheniscus demersus), also known as the African or black-footed penguin, received its common name because of its distinct donkey-like bray and its scientific name in reference to its small, plunging, wedged shape. Jackass penguins, known as Brilpikkewyn in Afrikaans, are the only penguins native to Africa and are found nowhere else. Their breeding range extends from central Namibia to the Eastern Cape Province of South Africa, and is determined mainly by the Benguela Current, which brings cold, nutrient rich water to the western coast of Africa, and by the availability of safe, off-shore islands as breeding sites (Davis and Renner, 2003).

Jackass penguins are small, about 60-70 cm in length, and can be recognized by a distinctive black chin and face patch separated from the crown by a broad white band (Williams, 1995). They also have bare, red patches above the eyes and a narrow, black band across their upper chest. They feed mainly on fish such as anchovies, sardines, and herrings, but also eat squid and crustaceans (Davis and Renner, 2003). These penguins are monogamous, and usually return to their partner and nest site year after year (Williams, 1995).

Spheniscus demersus

Penguins in general (see also Aptenodytes forsteri, the emperor penguin and Eudyptula minor, the Little Penguin) are highly derived avians with no clear relatives among other living birds, although most studies suggest that they are related to one among a number of seabirds. These possible sister groups include loons (Olson 1985), loons and grebes (Sibley and Ahlquist, 1990; Mayr and Clarke, 2003), or tubenoses (albatrosses and petrels; Simpson, 1946; Livezey and Zuzi, 2001; Bertelli and Giannini, 2005). This confusion is probably due to convergence among seabirds adapted to similar environments and to the fact that penguins evolved over 55 million years ago and have since undergone extreme morphological and genetic modification (Fordyce and Jones, 1990; Tambussi et al., 2005).

Relationships within penguins are also controversial and largely unresolved, although the six living genera almost certainly form natural groups. Jackass penguins belong to the genus Spheniscus, which also includes the Magellanic penguin (S. magellanicus), Humboldt penguin (S. humboldti), and Galapagos penguin (S. mendiculus). These Spheniscus penguins may be most closely related to the crested penguins (Eudyptes and Megadyptes) (Triche, unpubl. data), or to the little blue penguin (Eudyptula minor) (O’Hara, 1989). Spheniscus penguins are unique in sharing very deep, squared-off, triangular beaks, extremely deep temporal fossae that nearly meet at the midline, expanded salt gland fossae, and complete coracoid fenestrae (Bertelli and Giannini, 2005). They also possess a long and narrow retroarticular proces, very wide frontal bones, and a hinged fronto-nasal contact (Triche, unpubl. data). Spheniscus demersus specifically is probably the sister species to the S. humboldti (Triche, unpubl. data), which is extremely similar anatomically; Humboldt penguins are slightly heavier, with longer flippers and a narrower white band on their heads (Williams, 1995).

Penguins are entirely aquatic and have evolved numerous associated adaptations, including specialized salt glands (which allow them to drink salt water), extremely flattened wing bones, and a unique system of water-proof feathers (Davis and Renner, 2003). Although penguins probably originated in very southerly latitudes and then adapted to extreme cold weather (Triche, unpubl. data), Spheniscus penguins are even more derived and have re-dispersed north to inhabit South Africa and South America as far as the Equator. Spheniscus demersus has adapted to this warmer environment by being active only at dawn and dusk, nesting in burrows or other shelters as protection from the sun, and spending most of the day at sea or loafing on the beach.

Spheniscus demersus, which once numbered in the millions, is listed as “vulnerable” by the IUCN (World Conservation Union), with only 56,000 breeding pairs left in the world. The penguins’ decline is due mostly to human egg and guano collecting as well as competition with fishermen and oil pollution. All other Spheniscus penguins are threatened as well.

Additional Information on the Skull

Click on the thumbnails below for labeled images of the skull in standard anatomical views.

Dorsal view

Lateral view

Ventral view

About the Species

This specimen was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Nina Triche of the UT Department of Geological Sciences. Funding for scanning was provided by a UT Geology Foundation grant to Dr. Triche. Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

Lateral view of skull

Dorsal view of skull

Ventral view of skull

About this Specimen

The specimen was scanned by Matthew Colbert on 11 July 2005 along the coronal axis for a total of 954 slices. Each slice is 0.119 mm thick, with an interslice spacing of 0.119 mm and a field of reconstruction of 56 mm.

About the
Scan

Literature

Bertelli, S., and N.P. Giannini. 2005. A phylogeny of extant penguins (Aves: Sphenisciformes) combining morphology and mitochondrial sequences. Cladistics 21:209-239.

Davis, L. S., and M. Renner. 2003. Penguins. Yale University Press, New Haven. 212 pages.

Fordyce, R. E., and C. M. Jones. 1990. Penguin history and new fossil material from New Zealand. Pp. 419-446 in: L. S. Davis, and J. T. Darby (eds), Penguin Biology. Academic Press.

Giannini, N. P., and S. Bertelli. 2004. Phylogeny of extant penguins based on integumentary and breeding characters. The Auk 121:422-434.

Livezey, B, B., and R. L. Zuzi. 2001. Higher-order phylogenetics of modern Aves based on comparative anatomy. Netherlands Journal of Zoology 51:179-205.

Mayr, G., and J. Clarke. 2003. The deep divergences of neornithine birds: a phylogenetic analysis of morphological characters. Cladistics 19:527-553.

O’Hara, R. J. 1989. Systematics and the study of natural history, with an estimate of the phylogeny of the living penguins (Aves: Spheniscidae). Ph.D., Harvard University. 171 pg.

Olson, S. L. 1985. The fossil record of birds. Pp. 79-239 in: D. Farner, J. King, and K. Parkes (eds) Avian Biology vol 8. Academic Press.

Sibley, C. G., and J. E. Ahlquist. 1990. Phylogeny and classification of birds: a study in molecular evolution. Yale University Press, New Haven.

Simpson, G. G. 1946. Fossil penguins. Bulletin of the American Museum of Natural History 87:1-99.

Williams, T. D. 1995. The Penguins. Oxford University Press, Oxford.

Links

Spheniscus demersus page from the International Penguin Conservation Work Group

S. demersus page on the Animal Diversity Web (University of Michigan)

S. demersus page from the Southern African Foundation for the Conservation of Coastal Birds

pictures of S. dermersus on ARKive.org

Literature
& Links

Front page image.

Spheniscus demersus
Additional
Imagery

To cite this page: Dr. Nina Triche, 2005, "Spheniscus demersus" (On-line), Digital Morphology. Accessed October 24, 2014 at http://digimorph.org/specimens/Spheniscus_demersus/.

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