Marked nominative in Africa

Africa is a continent where grammaticalized case systems are a rare phenomenon. But there is one exception: East Africa is a region where there is a relatively high occurrence of case languages (that is, languages with a grammaticalized case system). With regard to the type of case systems which occur in Africa, again, the picture is crosslinguistically unbalanced as there are hardly any ergative languages. In other words, of the two most common case types worldwide, accusative and ergative(/absolutive), essentially only one is represented in Africa, namely the accusative type. From a worldwide perspective, Africa seems to be a continent where case has nothing special to offer. However, in East Africa there are so called marked-nominative languages which seem to be quite unique worldwide. They are somehow a mixture: On the one hand they share features with prototypical accusative languages, on the other hand they share features with prototypical ergative languages. In the present paper I will, first, define the typical features of a marked-nominative language. Second, I will give an overview of the languages which have a marked-nominative system. Third, I will deal with the question of whether the distribution of marked-nominative languages is genetically or areally motivated. And fourth, I will speculate on how such unusual systems could have developed.