Geoscience Reference
In-Depth Information
16
Plant and animal fossils in deserts
The discovery of fossil remains has been a very slow
and fortuitous process.
Charles Darwin (1808-1882)
The Descent of Man
(1871)
16.1 Introduction
Fossils have always played a major role in geology. For example, the geological time
scale was established on the basis of the presence or absence of certain fossils, with
particular emphasis on past extinctions, such as the disappearance of dinosaurs at the
end of the Mesozoic era 65.5 million years ago, as well as the first appearances of
certain distinctive plants and animals. The fossil fauna of our best-known deserts,
such as the Sahara and Gobi, bear witness to a vanished era when dinosaurs roamed
these once green lands. In addition to the fossilised bones of the former vertebrate
fauna, silicified tree trunks scattered across many present-day deserts point to a time
when they were once forested.
In geologically more recent times, only a few thousand years ago, small herds
of antelope, Cape buffalo, and occasional elephants and giraffes occupied the once
wooded grasslands of the Sahara (Jousse,
2004
), whose rivers and lakes supported
an aquatic fauna of fishes (including large Nile perch), turtles, hippos and crocodiles
(Vernet,
1995
). However, caution is needed here to not extrapolate too boldly from
the sporadic fossil remains. As Gautier et al. (
1994
) have reminded us: 'One elephant
doesn't make a savanna'.
Prehistoric rock art is an indirect form of fossil evidence. Scattered across the
Sahara, there are magnificent rock art galleries with depictions of the savanna fauna
engraved or painted wherever suitable rock outcrops offered fresh, smooth surfaces.
The older paintings focus on such animals as giraffes, elephants, gerenuks and
ostriches, while the later Neolithic images show scenes of cattle herding, including
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