Geology Reference
In-Depth Information
also notes that there is evidence for movement of
at least three species of geckos, all non-forest
forms, from the coast of West Africa to South
America by rafing on floaing vegetation and
debris. The rafing of repiles, especially snakes,
is known to occur during floods of the Rufiji River
in southern Tanzania (Moreau & Pakenham,
1941), but its relevance to the distribuion of for-
est fauna is still unclear.
examination of forest snakes, Hughes (1983)
noted that with the exception of the single mon-
tane Kenya endemic viper, Atheris desaixi, all the
species found in Kenya are also present in Zaire.
He notes further that, in general, there are few
endemic forest species of snakes.
In contrast, at least some genera and species
appear to have evolved in situ in the Easten Arc
forests or to have survived there in isolaion and
become exinct in all other African forests. Exam-
ples of such amphibian genera include the cae-
cilian Afrocaecilia and the microhylid frogs
Callulina, Probreviceps, Hoplophyne and Para-
hoplophyne. Calulina krfii was unil its discovery
in the T aita Hills regarded as a Tanzanian
endemic. Poynton (1964) regarded Pobrevicps as
primiive to Breviceps and noted that while both
were originally probably sylvicolous, the burrow-
ing ability of the latter allowed it to leave the forest
and occupy drier habitats, and Poynton & Broad-
ley (196 7) remarked upon the affinity of P.
rh oesianus, the only member of the genus ound
outside Tanzania, and Breviceps.
Aside from Arthrolptides matiensseni of the
Easten Arc only a single other species in the
genus, A. dutoiti, is described from Mount Elgon
in Kenya, but it may now be exinct or nearly so as
it has not been found by biologists during recent
searches (R. C. Drewes, personal communica-
ion). The only reptile genus that appears to have
arisen in the Easten Arc forests is Aenorhinos.
Many of the other species of the Easten Arc
forests appear to have evolved in situ. Schiotz
(1967, 1981) noted that while the separaion
between the eastern and Guineo-Congolian for-
ests is complete at the species level among ree-
frogs in the family Hyperoliidae, it is not possible
to ideniy species pairs or any other relaionship
below the genus level linking the easten and
westen forests. Those genera with notably large
numbers of species include the toads Nec-
tophynoies, the treefrogs Lptopelis and the
chameleons Chamaeleo and Rhampholeon. Fewer
endemics are found in the coastal forests. The
anurans Hy perolius rubnroermiculatus and Ar ixalus
sylvaticus are endemic to Kenyan coastal forests;
the skink Melanoseps onoensis and the lacerid
Gastopholis vittata are the only repiles endemic
Oriins of the Easten Arc orest
Given our lack of knowledge about many basic
fundamental factors which influenced the present
distribuion of forest amphibians and repiles,
such as exact iming and nature of the last con-
necions among various forests, climaic variations
and the rates at which speciation occurred, any
attempted 'explanaion' of the origin of the
Easten Arc fauna remains largely speculaive.
This is especially rue considering the lack of fos-
sil evidence for the area. Other than the dinosaurs
excavated by the Germans from Tendaguru 60
m northeast of Lindi early in this century
(Parkinson, 1930), the only other fossil repiles
recorded from Tanzania are those from Olduvai
Gorge (Rage, 1973, 1979; Meylan, 1983). Fossil
anurans have only recently been found in South
Africa (Van Djik, 1985) but none appear to be
known rom easten Arica (Tandy & Keith,
1972; Tihen, 1972).
Species with strong connections to the
Guineo-Congolian forests (see Table 9.1) indi-
cate the compleiies of interpreing and evaluat-
ing the effects of forest separaion between the
main westen and the outlying easten blocks.
Some forms are recognised as subspecies, while
others appear to show little variaion across their
enire range. That many of the Easten Arc forms
may have their origins in the Guineo-Congolian
forests is indicated by the fact that almost all the
genera present in the easten forests are also to be
found in the forests to the west. This is true even
for widely separated forms such as Nec-
tophynoides , with ive species in Tanzania, two
montane grassland species on Mount Nimba, and
two species in Ethiopia (Grandison, 1978). In an
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