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

Abstract

Nymphidae, the group of split-footed lacewings, is a rather species-poor group. Split-footed lacewings nowadays are restricted to Australasia, while fossil forms are also known from other areas of the world, indicating that the group was more species-rich and therefore likely diverse in the past. Split-footed lacewings have rather distinct larvae, roughly resembling antlion larvae, but differing from the latter especially with regard to the mandibles. Antlion larvae usually have three prominent teeth on each mandible, while at least extant larvae of split-footed lacewings only have a single prominent tooth per mandible. Fossils interpreted as larvae of split-footed lacewings are well known from amber from Myanmar (ca. 100 myr; Burmese amber) and by a single specimen from Baltic amber (about 40 myr). We here report additional fossil specimens from Myanmar amber, expanding the known record of fossil forms from six depicted specimens to 15. For the extant fauna, we could compile 25 larvae. We compare the diversity of shape of extant and fossil larvae through time using an outline analysis (based on elliptic Fourier transformation) of the head. The results of this analysis indicate that the morphological diversity, or disparity, of split-footed lacewing larvae was higher in the past than it is today. With this type of analysis, we can show a loss of diversity over time, without the necessity to identify the fossil larvae down to a narrow taxonomical range. A similar pattern has already been recognised in silky lacewings, Psychopsidae. This might indicate a general loss of diversity of lacewing larvae.

The first adult mantis lacewing from Baltic amber, with an evaluation of the post-Cretaceous loss of morphological diversity of raptorial appendages in Mantispidae

“…The record presented herein illustrates a striking decline in the Mantispidae morphological diversity over the course of the Cretaceous and Cenozoic. This trend illustrates yet another case of the drastic decline of the morphological diversity in an ingroup of Neuroptera (Haug et al 2021c).…”

Changes in the Morphological Diversity of Larvae of Lance Lacewings, Mantis Lacewings and Their Closer Relatives over 100 Million Years

“…Cases in which the same specimen had been re-figured were also included chronologically with reference to the original occurrence. While this includes a certain redundancy, it should represent the most complete way of cross-referencing, avoiding interpreting the same specimens as two independent occurrences (this way of presentation has also been used for other ingroups of Neuroptera [6,[15][16][17]). For an easier cross-reference to our dataset, we provide the dataset number here along with the specimen.…”

“…(4) Froggatt [103] provided a drawing of a larva labelled with the name Porismus strigatus indicating that it is a larva of Osmylidae. Yet, the larva is clearly a representative of Nymphidae [16,23,104]. Therefore, it could not be further considered here.…”

“…Still, the very distinct morphologies of lacewing larvae indeed provide some indication on their ecology. Haug et al [15][16][17] argued that morphological diversity of larvae can act as a proxy for their ecological diversity by using quantitative shape analysis. Such methods have also been used successfully for identifying similarities and differences in lacewing larvae [7,[18][19][20].…”

Lepidopteran caterpillars in the Cretaceous: were they a good food source for early birds?

“…If taxonomic or phylogenetic interpretations of fossil specimens are challenging, these are often difficult to be included into measures of diversity over time. Morphological aspects of such animals offer an alternative objective measure of diversity, independent from a taxonomic frame (see Haug et al 2020bHaug et al , 2021aHaug et al , 2021bHaug et al , 2021cHaug et al , 2021d.…”