An Expanded View on the Morphological Diversity of Long-Nosed Antlion Larvae Further Supports a Decline of Silky Lacewings in the Past 100 Million Years

SIMPLE SUMMARY: The insect group Neuroptera (lacewings) is often claimed to have been more diverse in the past than today. The same appears to have also been the case not only for the entire group Neuroptera, but also for several of its ingroups. Silky lacewings (Psychopsidae) are represented by relatively few species today. Their larvae, also called long-nosed antlions, can easily be identified by the following characteristics: they resemble antlion larvae, lack teeth in their stylets (mouthparts for catching prey), have trumpet-shaped attachment structures on their legs, and have prominent forward-directed upper lips (labra, singular labrum). Therefore, these larvae can also be recognised in the fossil record. An earlier study demonstrated a decline in the morphological diversity of long-nosed antlion larvae over the past 100 million years. Here, we report several dozen new fossil long-nosed antlion larvae. With these, we expand the earlier quantitative analysis. Moreover, in this study, we can show that the morphological diversity of long-nosed antlion larvae has decreased over the past 100 million years. However, we apparently do not have the full original morphological diversity of long-nosed antlions available, as there is no sign of visible saturation yet. ABSTRACT: Lacewings have been suggested to be a relict group. This means that the group of lacewings, Neuroptera, should have been more diverse in the past, which also applies to many ingroups of Neuroptera. Psychopsidae, the group of silky lacewings, is one of the ingroups of Neuroptera which is relatively species-poor in the modern fauna. Larvae of the group Psychopsidae, long-nosed antlions, can be easily identified as such in being larvae of antlion-like lacewings without teeth in their stylets (=compound structure of mandible and maxilla), with empodia (=attachment structures on legs) and with a prominent forward-protruding labrum. Therefore, such larvae can also be recognised in the fossil record. An earlier study demonstrated a decline in the morphological diversity of long-nosed antlion larvae over the past 100 million years. Here, we report several dozen new long-nosed antlion larvae and expand the earlier quantitative study. Our results further corroborate the decline of silky lacewings. Yet, a lack of an indication of saturation indicates that we have still not approached the original diversity of long-nosed antlions in the Cretaceous.