Fossil bee cells from the Canary Islands. Ichnotaxonomy, palaeobiology and palaeoenvironments of Palmiraichnus castellanosi

Abstract

Fossil bee cells, attributable to the ichnospecies Palmiraichnus castellanosi, are recorded from the Pleistocene and Holocene of the easternmost Canary Islands. Cells bear a chamber with internal smooth lining, spiral closure, and an antechamber. They have a discrete wall that surrounds both the chamber and antechamber. The antechamber shows an internal smooth surface and a structureless filling of palaeosol material. These features enable this material to be assigned to the ichnospecies P. castellanosi, originally described from the Palaeogene of Uruguay. This record constitutes the first documented evidence for bees, and Hymenoptera, in the Quaternary of the Canaries and the first for this ichnospecies from Africa. By comparison with extant cells, the potential constructors are bees of the genus Andrena (Andrenidae). Palaeoecological and statistical data suggest that five species may have produced P. castellanosi in the Canary Islands. One on Lanzarote in the Holocene, another in south Fuerteventura in the Upper Pleistocene, two on Gran Canaria and another on Montan&tild;a Clara islet during the Middle Pleistocene. A high level of breeding success was probably favoured by the lack of predators or parasites and optimal environmental conditions, at least in the Pleistocene. During the Pleistocene, the abundance of P. castellanosi in the lowlands suggests a rich endemic shrubby flora and palaeoclimatic conditions similar to the present, but probably with a higher humidity. The land-snail assemblage associated with low densities of P. castellanosi in the Holocene mid-altitude belt suggests a cool moist palaeoenvironment, less favourable for P. castellanosi producers.