X‐ray microtomography and phylogenomics provide insights into the morphology and evolution of an enigmatic Mesozoic insect larva

Fossils sometimes show unusual morphological features absent in livingorganisms, making it difficult to reconstruct both their affinity and their function. Wedescribe here a new lacewing larva, Ankyloleon caudatus gen. et sp.n. (Neuroptera) fromthe Cretaceous amber of Myanmar, characterized by an abdomen unique among insects,with ‘tail-like’ terminal segments bearing a ventral pair of vesicles. Phase-contrastX-ray microtomography reveals that these structures were dense and equipped with amedian duct, suggesting that they were likely pygopods used for locomotion, holding theposition through adhesive secretions. Our phylogenetic analyses, combining genomicand morphological data from both living and fossil lacewings, proved critical toplacing Ankyloleon gen.n. on the lacewing tree of life as an early representative ofthe antlion clade, Myrmeleontiformia. These results corroborate the view that derivedmyrmeleontiform lacewings ‘experimented’ with unusual combinations of features andspecializations during their evolutionary history, some of which are now lost.