# New Fossil Megalopteran and Megalopteran-like Larvae, a First Extinct Larval Morphology of Megaloptera, and Possible Larvae of Myxophagan Beetles

## TL;DR

This paper describes new fossil larvae that resemble dobsonflies, fishflies, and alderflies, revealing insights into their ancient morphology and evolutionary history.

## Contribution

The study presents the first extinct larval morphology of Megaloptera and suggests convergent evolution in larval traits.

## Key findings

- New amber fossils show a previously unknown larval morphotype with a terminal filament typical of Sialidae.
- Elongated prothorax and curved mandibles in some fossils suggest convergent evolution rather than ancestral traits.
- Quantitative analysis indicates no major morphological losses in megalopteran larvae over time.

## Abstract

We report new fossil larvae that have characteristics of Megaloptera, the group of dobsonflies, fishflies and alderflies. Older fossils from the Triassic are preserved as sedimentary fossils and younger ones from the Cretaceous and Eocene are preserved in amber. One of the new amber fossils shows more details than morphologically similar previously reported ones. The new details support the previous suspicion that the larvae are beetles, probably of the group Myxophaga. A statistical analysis was performed, indicating no large morphological losses over time. However, two newly reported larvae from amber have a today unknown morphology. The terminal filament indicates the larvae being representatives of Sialidae, alderflies. Untypical for the group is the elongated prothorax and strongly curved mandibles. This is more typical for Corydalidae, dobsonflies and fishflies. It is more likely that these characters are the results of convergent evolution instead of being ancestral characters.

We report new fossil larval specimens that have characters of the group Megaloptera, i.e., are either megalopteran or megalopteran-like larvae from the Triassic, Cretaceous, or Eocene. Fossils from the latter two times are preserved in amber. One of the new fossils reveals that some earlier reported presumed megalopteran-like fossils, that have been already suspected to be beetles, are indeed more likely beetles of the group Myxophaga. A quantitative morphological comparison supports that most fossil megalopteran (and megalopteran-like) larvae did not differ significantly from extant megalopteran larvae, indicating no major losses of morphology over time. However, two newly reported fossil specimens from Kachin amber indeed separate from the other larvae, representing an extinct morphotype. The morphotype is characterised by a prominent terminal filament, indicating that the specimen is a representative of Sialidae. However, unlike most of the known larvae of this group, it possesses a rather elongate prothorax and strongly curved mandibles. These two characters are more commonly known in larvae of Corydalidae. It seems most likely that the presence of these characters in the new morphotype does not represent a plesisomorphy, but is more likely the product of convergent evolution.