African fossiliferous amber: a review
Résumé
Amber has only rarely been found in Africa and the few known occurrences are
mostly devoid of organic inclusions. The first fossiliferous African amber was
reported a few years ago from Ethiopia, and was considered to be early Late
Cretaceous in age (Cenomanian, ~93-95 Ma). However, recent investigation of
additional amber material and associated sediment questions the previously assumed
age and provides compelling evidence that Ethiopian amber is Cenozoic, likely
Miocene. Support for this dating is based on both new and revised palynological
and palaeoentomological data. Insect fossils mostly belong to extant families and
genera. A particular reference to ants (Hymenoptera: Formicidae) is made here, with
the report of 51 individuals assignable to new extinct species of Dolichoderinae
(e.g. Technomyrmex), Formicinae, Myrmicinae (e.g. Melissotarsus, Carebara),
Ponerinae and Pseudomyrmecinae (e.g. Tetraponera). Chemical analysis indicates
that Ethiopian amber belongs to the Class le ambers typical of Fabaceae (although
the earliest record of a Class le amber dates back to the Carboniferous) and was
presumably produced by the genus Hymenaea, similar to East African Pleistocene
copals and Neotropical Miocene' ambers. Although much younger than previously
suggested, fossils in Ethiopian amber remain highly relevant as Miocene insects are
exceedingly rare in Africa.
The recent discovery of a new deposit offossiliferous amber is also reported
here, from the Early Cretaceous (Aptian, 113-117 Ma) of Congo-Brazzaville.
Chemically, Congolese amber belongs to the Class Ib typical of conifers, and the
family Cheirolepidiaceae is assumed to be the plant source. Amber nodules are dark
red in colour, with large pieces reaching up to 12 cm. The search for organismic
inclusions using conventional optical techniques is limited by the opacity of the
amber, but diverse arthropods and plant remains have already been found in few
more translucent pieces. A large survey using synchrotron imaging will be necessary
to evaluate the overall biodiversity of Congolese amber, the only fossiliferous amber
from the Cretaceous of Africa to date.