The Morphological Diversity of Antlion Larvae and Their Closest Relatives over 100 Million Years.

Abstract

Simple SummaryThe larvae of owlflies and antlions (here shortly embraced by the term “owllions”) are ambush predators. Their mouthparts are transformed into teeth-bearing stylets and used for catching prey and sucking, which is characteristic for neuropteran larvae. Here we used the morphology of the stylets and the head capsules of a large number of extant and fossil larvae as a proxy for the morphological diversity over time. The created dataset comprises outlines of stylets and head capsules of specimens from the literature, collections, databases and the herein described and depicted 38 fossil ones. Fossils in the whole dataset come from deposits with an age of about 20, 40, and 100 million years (Miocene, Eocene, and Cretaceous, respectively). In addition to the shape analysis of the outlines from the dataset, we conducted a statistical analysis as well. Eocene and Miocene samples did not result in a clear output, but Cretaceous samples allowed for some conclusions: The morphological diversity of owllion larvae increased over time, even though some morphologies of Cretaceous larvae went extinct.Among lacewings (Neuroptera), representatives of the groups Ascalaphidae (owlflies) and Myrmeleontidae (antlions) are likely the most widely known ones. The exact taxonomic status of the two groups remains currently unclear, each may in fact be nested in the other group. Herein, we refer to the group including representatives of both with the neutral term “owllion”. Owllion larvae are voracious ambush hunters. They are not only known in the extant fauna, but also from the fossil record. We report here new findings of a fossil owlfly larva from Eocene Baltic amber, as well as several owlfly-like larvae from Cretaceous Kachin amber, Myanmar. Based on these fossils, combined with numerous fossil and extant specimens from the literature, collections, and databases, we compared the morphological diversity of the head and mouthpart shapes of the larvae of owllions in the extant fauna with that of owllion-like larvae from three time slices: about 100 million years ago (Cretaceous), about 40 million years ago (Eocene), and about 20 million years ago (Miocene). The comparison reveals that the samples from the Eocene and Miocene are too small for a reliable evaluation. Yet, the Cretaceous larvae allow for some conclusions: (1) the larval morphological diversity of owllion larvae increased over time, indicating a post-Cretaceous diversification; (2) certain morphologies disappeared after the Cretaceous, most likely representing ecological roles that are no longer present nowadays. In comparison, other closely related lineages, e.g., silky lacewings or split-footed lacewings, underwent more drastic losses after the Cretaceous and no subsequent diversifications.