Geoscience Reference
In-Depth Information
moving camp and fishing from papyrus canoes (Muzzolini,
1995
; Coulson and Camp-
bell,
2001
). Prehistoric archaeological sites and the associated fossils of plants and
animals provide tangible evidence that the rock paintings and rock engravings often
represent day-to-day events in the lives of these prehistoric desert peoples. The plant
and animal fossils found in the lake and river sediments and in the relict soils preserved
in the deserts provide additional evidence with which to reconstruct past environments
and climates in these now arid regions.
The marine microfossil record off the coast of desert regions is often even more
useful than the terrestrial fossil record of past environments because it is generally
more continuous, is amenable to analysis of the stable isotopic composition of the
microfossils, notably foraminifera, and can usually be accurately dated. The aim of
this chapter is to consider the scope and limitations of using plant and animal fossils to
reconstruct climatic change in deserts. The subject is vast, but happily many excellent
specialist accounts are readily available relating to the use of fossil plants and animals
in reconstructing past environments on land and sea (Hill,
1994b
; Vrba et al.,
1995
;
Smol et al.,
2001a
;Smoletal.,
2001b
;McGowran,
2005
).
16.2 Desert refugia and disjunct distributions of plants and animals
In a comprehensive and still useful review of prehistoric environments in the Sahara,
the great Saharan scholar Theodore Monod noted that some elements of the earlier
savanna fauna have survived, albeit rather precariously, until the present (Monod,
1963
). In sheltered valleys in the rugged Aır Massif in Niger, near the southern margin
of the Sahara, there are remnant populations of baboons (
Papio anubis
) and patas
monkeys (
Cercopithecus patas
), which must have reached these desert mountains
during times of wetter climate when the West African savanna woodland was more
extensive than it is today (Monod,
1963
). They probably made use of riparian forest
corridors that grew along once permanent rivers flowing south from the mountains.
The Awash River that flows from the Ethiopian Highlands down into the Afar Desert
is a possible modern analogue, in that its banks and floodplain are thickly wooded
and support a modest primate fauna. The dwarf crocodiles that lived in some of the
permanent waterholes in the Tibesti Mountains of the south-central Sahara until the
1950s but have since been hunted to extinction were part of this climatic legacy
(Lambert,
1984
).
In the same volume inwhichMonod's overviewappeared,Moreau (
1963
) published
an important paper relating to the montane avifauna of Africa. He argued that montane
evergreen forest bird populations that were hitherto in contact became isolated during
geologically recent times of colder, drier climate, when the forests themselves became
isolated on particular mountains. A comparable study of disjunct populations, this time
of Amazonian
Heliconius
butterflies, concluded that fragmentation of the Amazon
rainforest during drier climatic intervals led to the isolation of the butterflies and is
