New aquatic insects from the Miocene of Australia with notes on the ecology and ontogeny of a new species of Chaoborus (Diptera, Chaoboridae)

Abstract

We describe a diverse aquatic insect assemblage from McGraths Flat, a Miocene Lagerstätte in central New South Wales, Australia that includes representatives of Sialidae, Limoniidae, Chironomidae and Chaoboridae. The aquatic insect fossils from this deposit consist predominantly of larvae. These include a new species of phantom midge (Chaoborus, Chaoboridae), three morphotypes of non‐biting midges (Chironomidae), one morphotype of cranefly (Limoniidae) and one morphotype of alderfly (Sialidae). The large number of fossil specimens enabled us to study the ontogeny of the new midge species. We discerned growth rates in fossil larvae, using morphometry of all four instars of Chaoborus. The simultaneous presence of taxa associated with still water and taxa associated with flowing water supports the hypothesis that McGraths Flat was deposited in an isolated water body (oxbow lake/billabong) with influence from a river during high water events.