247 million years old fossil flies may have been older than dinosaurs

During palaeontological research in the region a few years ago, Mallorcan researcher Josep Juárez made an unexpected discovery: a complete insect larva that had left a faint imprint of organic remains on the two sides, which were left exposed when the rock split in half.

The comprehensive analysis of the fossil had to wait, but when it was finally examined under a strong microscope, it became clear that it was a rare find.

The larva belongs to dipterans

The extremely well-preserved larva is from a family of insects called dipterans, which includes real flies, mosquitoes, midges, and gnats. The oldest dipteran ever discovered is this specimen, which dates to the early Middle Triassic and is 247 million years old—older than the earliest dinosaurs. 

Thousands of fossil dipterans have been discovered worldwide in thinly stratified rocks and amber. Fossils discovered in France, around one to two million years younger than those from Estellencs, previously held the record.

“While I was inspecting it under the microscope, I put a drop of alcohol on it to increase the contrast of the structures, and I was able to witness in awe how the fossil had preserved both the external and internal structures of the head, some parts of the digestive system, and, most importantly, the external openings to its respiratory system, or spiracles," said Enrique Peñalver, from the Spanish National Research Council (CSIC) at the Spanish Geological Survey (CN-IGME), and first author of the recently published study.

The study was published in Papers in Paleontology on 25 December, 2022.

Study abstract:

Insect colonization of continental aquatic ecosystems and their immediate surroundings was paramount for the establishment of complex trophic nets and organic-matter recycling in those environments. True flies and other insects such as mayflies developed crucial ecological roles in early continental aquatic ecosystems, as early as the Triassic. However, the mode and tempo of these processes remain poorly known, partly due to a critical fossil record gap before the Middle Triassic. Here we study the dipterans from the early Middle Triassic Konservat-Lagerstätte of Pedra Alta (Aegean, early Anisian, Spain), which yields the oldest records of the order. Protoanisolarva juarezi gen. et sp. nov., based on an exceptionally preserved larva, shares key features with the extant nematoceran family Anisopodidae. Developing in inferred moist terrestrial environments contiguous with pools inhabited by aquatic organisms, it represents the only known Triassic dipteran larva with terrestrial affinities indicating that the amphipneustic respiratory system of insect larvae extends back to c. 247 Ma. Two nematoceran aquatic pupae are also described: one classified as Voltziapupa cf. cornuta, and the other as an indeterminate taxon. Finally, an egg cluster belonging to the ootaxon Clavapartus latus is likely to have been produced by chironomids. These eggs were included in a mucilaginous matrix, a probable adaptation against predation and/or changing conditions, including desiccation. These new findings provide key data on the early evolutionary history of the mega-diverse order Diptera, the ecology of their ancestral pre-adult forms, and the functioning of early Middle Triassic continental aquatic ecosystems.