Mar. 26, 2013 — Africa isn't
the kind of place you might expect to find penguins. But one species
lives along Africa's southern coast today, and newly found fossils
confirm that as many as four penguin species coexisted on the continent
in the past. Exactly why African penguin diversity plummeted to the one
species that lives there today is still a mystery, but changing sea
levels may be to blame, the researchers say.
The fossil findings, described in the March 26 issue of the
Zoological Journal of the Linnean Society,
represent the oldest evidence of these iconic tuxedo-clad seabirds in
Africa, predating previously described fossils by 5 to 7 million years.
Co-authors Daniel Thomas of the National Museum of Natural History
and Dan Ksepka of the National Evolutionary Synthesis Center happened
upon the 10-12 million year old specimens in late 2010, while sifting
through rock and sediment excavated from an industrial steel plant near
Cape Town, South Africa.
Jumbled together with shark teeth and other fossils were 17 bone
fragments that the researchers recognized as pieces of backbones,
breastbones, wings and legs from several extinct species of penguins.
Based on their bones, these species spanned nearly the full size
spectrum for penguins living today, ranging from a runty pint-sized
penguin that stood just about a foot tall (0.3 m), to a towering species
closer to three feet (0.9 m).
Only one penguin species lives in Africa today -- the black-footed penguin, or
Spheniscus demersus,
also known as the jackass penguin for its loud donkey-like braying
call. Exactly when penguin diversity in Africa started to plummet, and
why, is still unclear.
Gaps in the fossil record make it difficult to determine whether the
extinctions were sudden or gradual. "[Because we have fossils from only
two time periods,] it's like seeing two frames of a movie," said
co-author Daniel Ksepka. "We have a frame at five million years ago, and
a frame at 10-12 million years ago, but there's missing footage in
between."
Humans probably aren't to blame, the researchers say, because by the
time early modern humans arrived in South Africa, all but one of the
continent's penguins had already died out.
A more likely possibility is that rising and falling sea levels did them in by wiping out safe nesting sites.
Although penguins spend most of their lives swimming in the ocean,
they rely on offshore islands near the coast to build their nests and
raise their young. Land surface reconstructions suggest that five
million years ago -- when at least four penguin species still called
Africa home -- sea level on the South African coast was as much as 90
meters higher than it is today, swamping low-lying areas and turning the
region into a network of islands. More islands meant more beaches where
penguins could breed while staying safe from mainland predators.
But sea levels in the region are lower today. Once-isolated islands
have been reconnected to the continent by newly exposed land bridges,
which may have wiped out beach nesting sites and provided access to
predators.
Although humans didn't do previous penguins in Africa in, we'll play a
key role in shaping the fate of the one species that remains, the
researchers add.
Numbers of black-footed penguins have declined by 80% in the last 50
years, and in 2010 the species was classified as endangered. The drop is
largely due to oil spills and overfishing of sardines and anchovies --
the black-footed penguin's favorite food. "There's only one species left today, and it's up to us to keep it safe," Thomas said.
Story Source:
The above story is reprinted from materials provided by National Evolutionary Synthesis Center (NESCent), via EurekAlert!, a service of AAAS.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Daniel B. Thomas, Daniel T. Ksepka. A history of shifting fortunes for African penguins. Zoological Journal of the Linnean Society, 2013; DOI: 10.1111/zoj.12024
National Evolutionary Synthesis Center (NESCent) (2013, March 26). Uncovering Africa's oldest known penguins.
ScienceDaily. Retrieved March 27, 2013, from
http://www.sciencedaily.com /releases/2013/03/130326101606.htm
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