New insect pupation chambers (Pupichnia) from the Upper Cretaceous of Patagonia, Argentina

Three new records of insect pupation chambers are reported from two localities in the Cretaceous Chubut Group of Patagonia, Argentina: from Sierra Nevada, a new and older ichnospecies of Rebuffoichnus, R. sciuttoi isp. nov. (Coprinisphaeridae), and the first Cretaceous and South American specimens of Pallichnus dakotensis Retallack (Pallichnidae), known until now from a single North American Oligocene locality; from Caٌadَn Puerta del Diablo, a new type of Rebuffoichnus casamiquelai Roselli that shows some differences from known material of the ichnospecies from the same locality, suggesting a different trace maker. Affinities of P. dakotensis, interpreted originally as a cast of a lined pupation chamber, remain unknown in the light of the new material. Its micromorphology is quite simple, with no constructed wall. R. sciuttoi has a very thinly constructed wall, showing an external texture composed of lobes and fine, helically arranged ridges. Such characters are compatible with those of wasp cocoons. R. casamiquelai, interpreted originally as a coleopteran pupation chamber, has a thickly constructed wall composed of two layers of soil material, showing redistribution of clay and orientation of long grains. Macro- and micromorphology of palaeosols indicate that in both localities pupation occurred in vitric entisols developed on pyroclastic ash-fall deposits on a fluvial floodplain. These new records double the number of the few Cretaceous insect pupation chambers. This is a critical period for understanding the origin and early evolution of building behaviour in insects. Three types of Cretaceous pupation chambers can now be recognized: (1) excavated and lined, e.g. Fictovichnus and Pallichnus (Pallichnidae); (2) constructed mostly with silk, resulting in thin-walled cocoons, e.g. R. sciuttoi (Coprinisphaeridae); (3) constructed mostly with soil material, resulting in thick-walled chambers, e.g., R. casamiquelai (Coprinisphaeridae). A new ethological category, Pupichnia, is proposed for grouping ichnotaxa representing pupation chambers, which, with Calichnia representing nests, comprises the two major types of insect trace fossils in palaeosols.