Discovery of the oldest known elmid larva (Coleoptera, Elmidae) from the Lower Eocene of Rajasthan (India, Palana Formation)

Abstract

A single elmid larva is reported from a laminate maroon shale bed of Gurha opencast lignite mine (Palana Formation, early Eocene, Bikaner District, north-western Rajasthan, India). It is the first fossil larva that can be attributed to Elmidae with certainty. A generic assignation is not possible, because the larva is strongly compressed, and the most important characters are not visible or poorly preserved. The larva is described morphologically and illustrated by photographs and line drawings. A larva of a holometabolous insect from Baltic amber, which was published recently as a member of Elmidae by Zippel et al. (2022), possesses no structural characters that would clearly suggest placement in this family. A photograph of the hitherto unknown larva of the extant Grouvellinus rioloides from Kyrgyzstan is included for comparison.