Insects of a Lost World

Meganeura is one of the most famous prehistoric insects and one of the enduring symbols of the Carboniferous period. This giant griffinfly — often described as a "giant dragonfly," though it was not a true dragonfly — had a wingspan of up to 70 cm and was the apex aerial predator in the swamp forests where it lived. Along with its close relative Meganeuropsis, Meganeura represents the upper size limit ever achieved by flying insects.

Description

Meganeura superficially resembled a modern dragonfly but was far larger. Its most striking feature was its wingspan, estimated at 65-70 cm based on fossil wing impressions. The body was elongate and robust, estimated at roughly 30 cm in length, with large compound eyes, short antennae, and strong, spiny legs adapted for catching prey in flight.

Like modern dragonflies, Meganeura was a member of the Palaeoptera — insects that cannot fold their wings flat against the body. Its wings were held outstretched at all times, as seen in modern dragonflies and damselflies. The wings themselves show the dense, regular venation pattern typical of the Meganisoptera.

Ecology and Behavior

Meganeura was almost certainly a predator. Its large compound eyes suggest excellent vision, and its spiny legs were well-suited to catching prey in mid-air, a hunting strategy (hawking) used by modern dragonflies. Its prey likely included other large flying insects, such as palaeodictyopterans and early orthopteroids, and possibly small vertebrates like early amphibians.

Like modern dragonflies, Meganeura likely had an aquatic larval stage, developing in the swamp waters of Carboniferous forests before emerging as a flying adult. However, direct fossil evidence of Meganeura larvae has not been definitively identified.

Why So Large?

The enormous size of Meganeura is directly linked to the high oxygen levels of the Late Carboniferous atmosphere. With oxygen concentrations reaching approximately 35%, the tracheal respiratory system of insects could support much larger body sizes than would be possible at modern oxygen levels (21%). Laboratory experiments with modern insects raised in oxygen-enriched environments have shown increased body size, supporting this hypothesis.

Additional factors may have contributed: the absence of flying vertebrate predators (birds and bats had not yet evolved) meant there was less competition for aerial ecological niches, and plentiful prey in the form of other large Carboniferous insects provided a sufficient food base.

Discovery

Meganeura was first described by the French paleontologist Charles Brongniart in 1885, based on a fossil found at Commentry in central France. The Commentry coal mines had yielded numerous Carboniferous insect fossils, and the Meganeura specimen was immediately recognized as exceptional. The type species is Meganeura monyi.

Meganeura vs. Meganeuropsis

Meganeura is often confused with Meganeuropsis permiana, a closely related griffinfly from the Early Permian of Kansas. Meganeuropsis was slightly larger, with an estimated wingspan of up to 71 cm, making it the largest flying insect ever known. Both belong to the order Meganisoptera, which went extinct by the end of the Permian period.