Trace fossils of cicadas in the Cenozoic of Central Patagonia, Argentina

Abstract

Hemispherical pan or dish-shaped trace fossils from the Cenozoic of the Central Patagonia are attributed to the burrowing action of cicadas. A new ichnotaxon, Feoichnus challa igen. et isp. nov. is characterized by its hemispherical shape, mostly subvertical orientation, smoothed internal lining showing knobbly surface texture, and rough and irregular external surface devoid of ornamentation. The wall is composed of a lining plus a layer of soil material consolidated passively by cicada excretions. In other specimens the wall shows a repetition of linings and soil layers reflecting changes in the position of the chambers. Grooves, which represent traces of roots originally related to the feeding activities of cicada nymphs, are located in the wall of many specimens of F. challa. These grooves are subvertical to subhorizontal and show smooth surfaces with longitudinal striations. The cicadan origin of these traces is supported by comparison of the fossils to modern cicada nymph chambers and by laboratory experiments. The most significant characters that emerged from the comparison are the differential preservation of the basal part of the chambers, the interior lining with similar surface texture, and the presence of root traces in the wall and in the interior of the chamber. Additional records of F. challa from the Cretaceous-Pliocene of the USA, the Oligocene of Ethiopia, and the Miocene of the United Arab Emirates and Kenya complete the current information yielded by the known body fossil record to help understand the evolutionary history of cicadas.