Scytinopterid (insecta: Hemiptera) richness during the late triassic in south-western Gondwana (Argentina)

Abstract

The Triassic Period was a heyday for scytinopterids, which were represented by diverse and disparate taxa. Their small size, the selection of shore plants as a resource for living, and a non-specialized diet allowed them crossing the Permian-Triassic limit and retaining the dominance and diversity through the Late Triassic. The Family Scytinopteridae ecologically characterized Triassic biotas alongside with Progonocimicidae, Dunstaniidae, Hylicellidae, Dysmorphoptilidae, and other derived scytinopteroid families. Contrary to the Permian, where most fossil information is based on discoveries from the Northern Hemisphere (e.g., Russia, France), during the Middle-Late Triassic, records of Scytinopteridae come mainly from Argentina and Australia, and in less proportion, Russia, Kyrgyzstan, and China. However, despite the large number of specimens collected worldwide, both Superfamily Scytinopteroidea and Family Scytinopteridae are groups in need of a complete revision and phylogenetic analysis. Recently, abundant and well-preserved scytinopterids (~200 specimens) were collected from the uppermost part of the Potrerillos Formation (Carnian) at the Quebrada del Durazno locality, south of the Cerro Cacheuta, Cuyana Basin, Mendoza Province (Argentina). The scytinopterids, and hence the Hemiptera order, is the dominant group at the locality, but sometimes they are over-represented in oryctocoenoses (taphonomic bias and/or habitat type). Other insect groups recorded at the locality include mecopterans, dipterans, odonatans, orthopterans, grylloblattids, beetles, and miomopterans. The scytinopterids collected mainly comprise sclerotized forewings (tegmina), disarticulated (without clavus), preserved as compressions and impressions. Preliminary taxonomic analysis observed between the Argentinian and Australian taxa (e.g., venational pattern, size, ornamentations on forewing) suggest these two hemipteran faunas potentially represent distinct subfamilies. Additionally, we observed that the Argentinian scytinopterids were distinctly bigger (~19-28 mm) than the Australian ones (~5-11 mm), probably as a consequence of the different paleoclimatic conditions. The scytinopterids had an amphibiotic lifestyle; at the Quebrada del Durazno locality, the insects lived on waterside vegetation (e.g., sphenophytes) growing in the delta plain under temperate-warm and humid conditions by maximal development of the megamonsoon during the early Late Triassic. Likewise modern hemipterans, the scytinopterids were phytophagous (with piercing-and-sucking habits) and probably fed on the various seed plants, abundantly represented at the Quebrada del Durazno locality. The Scytinopteridae richness recorded at the Potrerillos Formation indicates that the family was a key component in Late Triassic land ecosystems, and acted as primary consumers after the P/T mass extinction in entomological communities.