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 modernecosystems. Inland, these changes included an outstanding turnover between amniote groups triggered by thediversification of plants and arthropods. A super-radiation of morphologically modern insects occurred in theTriassic, including some of their most successful and ecologically relevant groups, such as Diptera (flies andmosquitoes) 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 acommunal latrine in the lower Carnian deposits (~236 Ma) of the Chanares ˜ 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 Chanares ˜ scales would partiallyfill the temporal mismatch between phylogenomic date and the fossil evidence of butterflies and moths becausethey preceded the previously oldest lepidopteran record by c. 35 million years. Moreover, the scales have acombination of features present in early diverging glossatan lepidopterans. The inclusion of the temporal dataprovided by the Chanares ˜ scales into an updated temporal calibration of lepidopteran phylogeny shows that theproboscis, a key evolutionary novelty for the group (Glossata), evolved between c. 260–244 Ma. Thus, theproboscis-bearing lepidopterans would be part of the repertory of new plants and animals that diversified duringthe aftermath of the EPME.