Back to the poop: the oldest hexapod scales discovered within a Triassic coprolite from Argentina

Abstract

Life on Earth nearly came to an end during the end-Permian mass extinction (EPME; c. 252 Ma). In its aftermath, the Triassic witnessed the adaptation of survivors to a postapocalyptic world and the establishment of modern ecosystems. Inland, these changes included an outstanding turnover between amniote groups triggered by the diversification of plants and arthropods. A super-radiation of morphologically modern insects occurred in the Triassic, including some of their most successful and ecologically relevant groups, such as Diptera (flies and mosquitoes) and Lepidoptera (moths and butterflies). Here, we describe the oldest evidence of hexapod scales, preserved within a megaherbivorous kannemeyeriiform dicynodont coprolite. This specimen comes from a communal latrine in the lower Carnian deposits (∼236 Ma) of the Chañares Formation, La Rioja Province, northwestern Argentina. The tiny fossil scales are hollow and ornamented, which is a synapomorphy of Lepidoptera and suggests that they could belong to this group. If this is the case, the Chañares scales would partially fill the temporal mismatch between phylogenomic date and the fossil evidence of butterflies and moths because they preceded the previously oldest lepidopteran record by c. 35 million years. Moreover, the scales have a combination of features present in early diverging glossatan lepidopterans. The inclusion of the temporal data provided by the Chañares scales into an updated temporal calibration of lepidopteran phylogeny shows that the proboscis, a key evolutionary novelty for the group (Glossata), evolved between c. 260–244 Ma. Thus, the proboscis-bearing lepidopterans would be part of the repertory of new plants and animals that diversified during the aftermath of the EPME.