Iridescent harvestmen (Arachnida: Opiliones: Sclerosomatidae) from the Eocene of Messel, Germany

Abstract

The first fossil harvestmen (Arachnida: Opiliones) from the Messel Pit in Hesse, Germany, are described as ?Leiobunum messelense sp. nov. and ?Leiobunum schaali sp. nov. This is the first formal description of fossil harvestmen from the Eocene (ca. 47 Ma) of Messel, and one of the few non-amber records of harvestmen in the Cenozoic. Remarkably, these new specimens show iridescent, metallic colouration. This was previously unknown in the arachnid fossil record, but is seen often in insect fossils from Messel. The new harvestmen exhibit the typical ‘daddy long legs’ morphotype, with small, rounded bodies and long, slender legs. In detail, most of the dorsal opisthosomal tergites appear to be fused together into a single large scute, or scutum parvum, which strongly suggests the modern family Sclerosomatidae, especially in combination with a pectinate pedipalp claw. The iridescent colouration further implies that these fossils can be referred to either the subfamilies Gagrellinae or Leiobuninae, some of which also have a characteristic metallic lustre. Iridescence of the body is more typical for tropical sclerosomatids and is not known from extant European sclerosomatids, with the exception of a single, probably invasive, Leiobunum species. The warmer temperatures during the Eocene might have allowed exchange of early iridescent sclerosomatids between Eurasia and North America, which led to their wide present day distribution and diversity. A few not very well preserved harvestman fossils from Messel are recorded and/or figured for completeness as Leiobuninae / Gagrellinae indet. and Opiliones indet.