First fossil insect record from the Arroyo Totoral Formation (Lower Permian), Paganzo Basin, La Rioja Province, Argentina

Abstract

The Permian entomofaunas (~290–252 Ma) were characterized by many Carboniferous groups, but they also marked the origin of new insect orders such as the basal relatives of plecopterans, mecopterans, psocopterans, and beetles. During this time, new mouthpart types (e.g., stylate piercing-and-sucking) and functional feeding activities appeared, hence the seeking of new food sources, which led to the diversification, evolution, and expansion of the herbivorous insects. More than 35 fossil insect species, represented by forewing impressions, have been collected and described from different Permian outcrops of Argentina, Brazil, and Uruguay. In Argentina, the insect records come from the Bajo de Véliz (Paganzo Basin, San Luis Province) and Río Genoa (Tepuel Genoa Basin, Chubut Province) formations. The fossils include both terrestrial phytophagous and detritivores insects such as palaeodictyopteroids (e.g., megasecopterans Sphecorydaloididae, Diaphanopteridae, Breyeriidae), polyneopteran "protorthopterans" (Proedischiidae) groups, and "cockroachoids" (Phyloblattidae). Here, we present the first fossil insect from the Arroyo Totoral Formation (early Lower Permian), south of Sierra de Los Llanos, in the eastern sector of the Paganzo Basin, southeastern La Rioja Province, Argentina. The specimen consists of a compression of a single right forewing, collected by "Macuca Team" during fieldwork carried out in 2022/2023 in Arroyo Totoral outcrops, and is housed at the Colección de Paleoinvertebrados, Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de la Rioja (CRILAR-CONICET), under the CRIPI acronym. The fossil is associated to a diverse paleoflora including glossopterids, pteridosperms, conifers, cordaitaleans, ferns, and sphenophytes, which developed under local humid conditions for the Sierra de Los Llanos area during Permian times. Based on the general venation scheme that include an elongated and comparatively narrow costal field, widened areas between the main veins (e.g., Sc, R), Sc pectinated, with branches mostly simple and nearly straight; this new specimen can be tentatively attributed to the predominantly Paleozoic Family Phyloblattidae (stem-Dictyoptera). This finding represents the first known early Permian insect found for both the La Rioja Province and Arroyo Totoral Formation pointing the unit as a new promising site for the search of fossil insects in Argentina. Future paleontological prospections in this formation will undoubtedly enrich our understanding on the diversity of insects during their early evolution.