The decline of silky lacewings and morphological diversity of long-nosed antlion larvae through time

Abstract

Psychopsidae (silky lacewings) is a species-poor ingroup of Neuroptera. Silky lacewings show a distinct relic distribution, indicating that the group was more speciesrich and diverse in the past. Silky lacewings have distinct larvae that resemble antlion larvae but differ from these in lacking teeth on their mouth parts, and in having a projecting labrum, which makes them "long-nosed antlion larvae". These larvae are well known from Myanmar amber (about 100 mya) and Baltic amber (mostly 34-38 mya, possibly 23-48 mya), as well as from the extant fauna. We report and figure numerous additional specimens from both amber types and from ca. 100 mya old French Charentese amber, expanding the known record of well-illustrated extant and fossil specimens from 26 to 52 specimens. We compare the diversity of head shape among these larvae through time by outline analysis. Results indicate that morphological diversity was pronouncedly higher in the Cretaceous, even after sample size correction. Eocene representatives are more diverse than modern representatives, but less diverse than Cretaceous ones, in one shape aspect that explains most of the overall variation (55.7%). Eocene representatives are less diverse in another shape aspect that explains the second-most variation (26.9%), but this might reflect a lack of first larval stage specimens. There seems to be no strong correlation between size and shape. This type of analysis enables a test for the loss of diversity over time, based on morphological diversity as a proxy, without the requirement of identifying fossil larvae down to a narrow taxonomical range.

Eco-morphological diversity of larvae of soldier flies and their closest relatives in deep time

“…The ecomorphotype, or a shape of an organism adapted to a certain ecological condition, is used here as a proxy for the diversity of forms within a group of organisms ( Haug et al, 2020b ). Outlines of the entire body, or parts of it have been shown as superior proxies for the shape of an organism in many cases, when landmarks are hard to define, or when such landmarks do not reflect the shape of the organisms well enough ( Tatsuta, Takahashi & Sakamaki, 2018 ).…”

Split-footed lacewings declined over time: indications from the morphological diversity of their antlion-like larvae

“…While we have seen already higher values in other analyses (e.g. Haug et al 2020), this value is still acceptable. PC1 and PC2 are used for most of the plots, in one plot all eight effective PCs are shown.…”

“…Having only such a low number of larvae available is, unfortunately, a general pattern (e.g. Haug and Haug 2019;Haug et al 2020). This overall apparent ignorance against larvae is not easy to understand.…”

“…The important criterion was a well-accessible posterior rim of the head capsule. Redrawn images were analysed in SHAPE (see also Braig et al 2019;Haug et al 2020 for details).…”

A Bizarre Planthopper Nymph (Hemiptera: Fulgoroidea) from Mid-Cretaceous Kachin Amber

“…The most striking morphological feature of the fossil is its body covered by numerous spines and tubercles (i.e., armour). Such structure is common among some insect larvae from mid-Cretaceous Kachin amber [ 29 , 30 , 31 , 32 ], but very rare in extant and extinct planthoppers. By the Early Cretaceous, many new predaceous arthropods (including some spiders, lacewing larvae, and ants) and vertebrates (including lizards, birds, and mammals) had appeared [ 33 , 34 , 35 ], so S. shcherbakovi probably used these spines and tubercles to protect itself from predators.…”