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The extant insects witnessing the pasts of Africa: essay on the origin and singularity of the Afrotropical entomofauna. This essay on the evolutionary history of the Atrotropical insects puts together the systematic and the evolution of many groups of insects with the large features of the geological, palaeobiogeographic and palaeoenvironmental history of the African continent. It is carried out starting from a synthetic approach, which endeavours to analyse some broad outlines of the origin of the diversity of entomological faunas of this area.

The general history of the insects on a world scale is rather well-known thanks to the fossils and began around 400 Myr ago with the first recognized insect fossils. On the African continent, fossil insects remain relatively rare, or little studied, outside several deposits in Southern Africa, which show a high entomological diversity. The first known fossil traces in Africa go back to the Permian (250290 Myr) from Madagascar (Orthoptera) and South Africa, with the Whitehill Formation (Coleoptera: Permocupedidae). The first African record of a modern-like fauna is Triassic (Molteno site: 200-250 Myr). Modern lineages truly diversified during the Cretaceous (Orapa site: 89-93 Myr). Despite the importance of these sites they are not truly representatives of the evolution of African insect faunas, in particular during the Tertiary period, when the African fauna acquired its originality. The Coleoptera: Scarabaeoidea came from Jurassic lineages but they mainly evolved during the Cenozoic with a crucial phase during the lower Oligocene for the coprophagous species due to the rapid radiation of the herbivorous mammals. Infortunatly, very few fossil Scarabaeoidea have been described from Africa. Africa draws its specificity, as a biogeographic area, from the breakup of the Gondwanaland at the Cretaceous times. Did the old geographical continuity between the continents of the southern hemisphere have an influence on the extant faunas of these areas and in particular of the Afrotropical region? The taxa that present disjunct distributions on several parts of the southern continents are generally qualified Gondwanian. They have remarkable rates of endemicity and one does not know a current representative to them out of the southern areas of the Southern hemisphere continents. However, the fossils suggest that these disjunct distributions could have been the results of processes of post-gondwanian extinctions rather than of the maintenance of original endemisms. The Mantophasmatodea, which are today endemics to Southern Africa, are known from the Eocene Baltic amber and the Middle Jurassic of China. It would be thus more judicious to use for these organisms the epithet of Mesozoic instead of Gondwanian taxa. Trans-Thethys exchanges between Africa and the Laurasian continent are well documented for the Vertebrates and for some insect taxa.

One of the key periods of the splitting of Gondwana is the final separation of the African and South American continents at the beginning of the late Cretaceous at about 95 Myr ago. However Africa shares few living taxa with the American continent and the origin of these common elements seems very diverse. It is first of all necessary to draw aside the species which profited from human transport. It is the case of various pests and some of their antagonists. Then, some genera common to Africa and Americas could be recognized, like Schistocerca (Orthoptera) or Mallodon (Coleoptera). The origin of the genus Schistocerca took place in the Old World and it strongly diversified in South and Central America after a recent event of transatlantic migration, fortuitous and doubtless single. The most attended way of passage was the strait of Behring, but it imposed on taxa a capacity with adaptation to the cool or cold climates which reigned in this area after the Miocene. It did not allow the migration of number of warm intertropical taxa. The disjunctions in the chorologies of the genera or the families illustrate the oldness of some taxa. Examples are observed particularly in the Orthoptera: Charilaidae, some Diptera: Bombyliidae and the tribe Fideliini (Hymenoptera: Megachilidae).

The great biogeographic areas of the Afrotropical region where set up during the great biological events that modelled the floras and faunas from the Cretaceous to the Neogene. The end of the Cretaceous is supposed to be marked by a major biological crisis but this did not affect the insect families to a significant degree. The great changes at the family level in insects and the angiosperms occurred much earlier, at the beginning of the late Cretaceous (Cenomanian-Turonian). Many plant or animal taxa disappear, while a new angiosperm flora and its associated fauna developed. Later, during the Neogene, the African continent was the theatre of an explosion of biological forms adapted to graminaceous environments in relation with climate changes.

Another key period for the Afrotropical insect fauna is the restoration of the contact between the African tectonic plate and the Eurasiatic plate in Miocene at about 17 Myr, or earlier at the end of the Oligocene. Three biogeographic regions of the Old world, the Palaearctic, Oriental and Afrotropical regions shared many taxa at various times of their history. The setting in physical contact of the Eurasiatic and African plates reinforced the interchanges between these areas. The high level of exchange did not prohibit the maintenance of a strong endemicity. Southern Africa is characterised by a remarkable endemic fauna. If some of these endemic taxa correspond perfectly to the so-called Gondwanian relicts, geographical isolation contributed to the originality of the local evolutionary processes, processes which could have been accelerated by particular ecological conditions, viz, the cases of the Tenebrionidae and some Scarabaeidae endemic to the Namib Desert.

The intertropical area of the continent was the melting pot of the evolution of forest faunas. The more or less continuous forest belt of the Paleogene experienced a long story of fragmentation and rebuilding from the Miocene until today which, by-effect, contributed to divide the forest phylla into multiple species and populations. The systematic of the recent forest insect genera is the result of this chaotic history. The mountains of the Afrotropical region also played a determining role in the structuring of insects faunas. The entomofaunas of sub-Saharan mountains appear less diversified than the one observed in the Eastern and Neotropical regions, but it clearly indicates complex affinities and old migrations between the large current faunistic blocks like the East African and the Guineo-Congolese areas. The sub-mountain forests of the Miocene volcanoes of the Volcanic Line of Cameroon, as the pre-Miocene granitic mountains of the Eastern Arc in Tanzania functioned like "continental islands" during at least 10 million years. They generated a great number of endemic forms. The Volcanic Line of Cameroon played a very important role in the structuring, the circulation, and in the isolation of the faunistic components, not only the mountainous one, but especially of the species adapted to mid-altitudes which especially developed in Eastern Africa following the raising of the East and the Centre of Africa.

The role of the African Rift is still difficult to appreciate. The faunistic studies are very generally restricted to sub-regional analyses or remain simply descriptive. Except the analyses of the mountain faunas, few syntheses compare the Western and Eastern African regions. The complexity of the evolutionary forces at work, global rising of the Eastern Region, recent volcanicity, presence of old mountainous chains, drying of the climate in the East and maintenance of large forests blocks in the West, complicates the analysis of the message contained in today faunas. This is a research field full with promises on the condition that it will be extended beyond the single role of the Rift.

All the elements presented here show that the entomofauna of the Afrotropical region is a composite assemblage of old, young, and incipient species that illustrate the diversity of the evolutionary stories which proceeded in this area. Through their diversity, the insects are an incomparable model for the study of the terrestrial ecosystems and the knowledge accumulated by taxonomic and faunistic work offers a vast field of investigation to be explored thanks to the modern tools of biology.