Miocene instead of cretaceous: a reappraisal of the age of Ethiopian amber

Amber from Ethiopia has been initially reported as supposedly deriving from a geologic unit named the Debre Libanos Sandstone and dated as early Late Cretaceous in age (Cenomanian, ca. 93–95 Ma). But the subsequent discovery of almost exclusively extant genera among the enclosed arthropods questioned the assumed Cretaceous age. Here, we re-examined palynomorphs from material of the previous study and investigated additional material obtained from fieldwork in the Amhara Region or available from various collections. Our new geological, geochemical, palynological, and palaeoentomological data provide compelling evidence for a younger, Cenozoic age of the amber, most likely Early Miocene (16–23 Ma). Palynomorphs from the amber-bearing sediments have yielded large numbers of typically long ranging Cenozoic pollen, some of which are particularly abundant in Lower Miocene layers of nearby basins of South Sudan. The chemical characterization of the amber and palaeobotanical data suggest that the resin was produced by a legume tree (Fabaceae), likely Hymenaea or a close relative in Detarieae. Fossil arthropods and plants retrieved from the new amber samples show a high diversity and are typical of assemblages in Neogene ambers. A particular reference to ants (Hymenoptera: Formicidae) is made here, which include 245 individuals mostly assignable to extant genera within the subfamilies Dolichoderinae, Myrmicinae, Ponerinae, and Pseudomyrmecinae, and only few extinct or undetermined genera. Ethiopian amber inclusions show that tropical moist forests persisted on the Ethiopian Plateau until the Early Miocene. Although Ethiopian amber is much younger than previously assumed, it is of exceptional value as it is one of only two fossiliferous African ambers known to date, and as Miocene forest biomes are exceedingly poorly documented in Africa.