The West African fauna has lacked not only zebras but also grazing rodents

@maxallen @douglasriverside @oebenin @galat-luong_anh @galewski @zarek @tom_crassard @elisebakker @tandala @oviscanadensis_connerties @jeanpaulboerekamps @mschmidt1966 @i_c_riddell @ricky_taylor @ludwig_muller @jason_van_den_berg

Zebras (Equus spp.) are absent from West Africa (, despite the presence of up to five species in southern and eastern Africa over the past ten thousand years.

It is easy to assume that this absence is because zebras were:

  • formerly present but have been exterminated, and/or
  • ecologically replaced by an extinct form of wild ass.

However, there seems to be no palaeontological or archaeological evidence of zebras anywhere in West Africa - even in the Pleistocene.

Human populations have long been denser in West than in southern Africa, and this is known to have drastically reduced the geographical ranges of wild ungulates - in several cases to the point of near-extermination from West Africa. However, even the giant eland (Taurotragus derbianus) and a giraffe (Giraffa camelopardalis peralta) still remain in small numbers.

It is likely that a form of wild ass, now extinct owing to human influence, formerly occurred in the western Sahel ( However, this would still leave a large area of savannah ( - as extensive as the whole of South Africa - naturally devoid of wild equids.

The point of this Post is that a similarly puzzling absence also applies to certain members of the grazing guild that are so fecund that their extermination by humans has been out of the question.

Otomyin murids ( are common and diverse in southern Africa and are specialised for fibrous foods similar to the diets of zebras and asses.

Otomys, Myotomys and Parotomys resemble voles ( and tropical American grazing rats (, and They are among the most strictly herbivorous of rat-like, non-amphibious rodents.

The jaws of otomyins are noticeably massive ( and and and their molars are adapted for grinding fibrous greens (

Two of the many species of otomyin rodents do marginally reach West Africa: Otomys occidentalis and Otomys burtoni ( However, these are disjunct relative to the distribution of the rest of the genus, the closest species of which occurs in northern Angola, two thousand kilometers away.

In addition, a large-bodied grazing rodent, Thryonomys gregorianus (, is widespread in eastern Africa from southern Zimbabwe northwards - but hardly reaches West Africa.

The absence of these specialised grazing rodents from West Africa can hardly be attributed to human influence. Therefore there seems to be something fundamental in the ecology of this region that has limited the niches of non-ruminant grazers.

The only two species of specialised grazing rodents widespread in West Africa, namely Thryonomys swinderianus ( and and Dasymys rufulus (, are:

  • largely restricted to the vicinity of permanent water, and
  • shared with southern Africa at the level of species (T. swinderianus) or genus (Dasymys).

Arvicanthis niloticus solatus ( and Arvicanthis ansorgei ( fill In ecologically for otomyins to some extent in West Africa, having similar body mass (approximately 100 grams) and eating grasses as staples. However these rats are not as specialised as otomyins and do not resemble voles.

What emerges is an anomalous lack of both zebras and grazing rodents in West Africa.

And, come to think of it, is there any evidence for that even larger specialised grazer, the square-lipped rhino (Ceratotherium simum,, occurring in West Africa - even in the Pleistocene?

Can any reader propose a reason why wild grazers across this large range of body sizes (100 grams to two tonnes) have been unsuited to the savannahs of a wide swathe of Africa from Senegal through Burkina Faso to eastern Nigeria?

Posted on February 15, 2022 02:46 AM by milewski milewski


Posted by milewski over 2 years ago

Add a Comment

Sign In or Sign Up to add comments