New Data Indicate Larger Decline in Morphological Diversity in Split-Footed Lacewing Larvae than Previously Estimated.

Modern insect decline sparks interest in similar declines of the past. Neuroptera, the group of lacewings, has been suggested to have undergone decline after the Cretaceous, and quantitative studies of larval morphology have supported this view. One of the groups within Neuroptera seeing a major decline is that of split-footed lacewings, Nymphidae. We here report 13 new larval specimens of split-footed lacewings from about 100-million-year-old Kachin amber, Myanmar. We explore how enlarging the data set to 60 specimens and expanding the investigated morphological structures affect the recognition of decline. The expanded data set has an increased morphospace, indicating a lack of saturation. The decline is, therefore, likely even larger than so far anticipated for Nymphidae. The study of head and mouthparts provides the strongest signal for a loss of diversity, which is feasible due to the direct coupling to feeding ecology. Analysis of the trunk region cannot recover a signal for loss of diversity. Sampling issues play a role here: the trunk of the larvae is less often well preserved, and the fossil larvae are more likely in early developmental stages due to the constraints of preservation.