Carboniferous fossils preserve insects unlike those alive today. The best-known is Meganeura monyi, a giant griffinfly from Late Carboniferous coal-bearing deposits at Commentry, France. Its wingspan is commonly estimated at about 65–70 centimetres. The fossils show a flying insect far larger than most modern species, but it was not simply an oversized modern dragonfly.
What the fossils preserve
Many Carboniferous insects are flattened impressions in fine sediment. Wing veins can be clear enough to identify a group and estimate dimensions. A measured wing is direct evidence; a complete body length, mass or colour is reconstructed from incomplete remains and comparisons with related insects.
Meganeura belonged to Meganisoptera, an extinct group often called griffinflies. “Giant dragonfly” is a convenient label, but can imply a closer relationship to living dragonflies than the fossils support. The Meganeura fossil record provides a striking example of ancient insect scale.
A world of coal swamps
During parts of the Carboniferous, extensive lowland wetlands accumulated plant material that later became coal. Tall lycopsid trees, horsetails and ferns formed habitats very different from modern forests. Fossil beds preserve plants, arthropods and other animals, though no single layer captures a complete living community.
Large griffinflies were aerial predators. Fossils preserving parts of their anatomy, combined with biomechanical comparisons, support a hunting lifestyle. Exactly how they flew through vegetation, selected prey or reproduced is harder to infer. A reconstruction in a swamp canopy is plausible context, not a frozen scene from one quarry.
Did high oxygen create the giants?
Insects breathe through a branching tracheal system. This inspired the idea that elevated atmospheric oxygen in the Late Palaeozoic eased oxygen delivery and allowed greater body size. Experiments and models support a role for oxygen in insect physiology, and giant insects occur during intervals when some reconstructions suggest higher oxygen.
But correlation does not prove oxygen alone caused gigantism. Ancient atmospheric estimates are uncertain, the fossil record is patchy, and large insects persisted into intervals when oxygen may have been lower. A 2026 study found that oxygen supply through the tracheolar-muscle system did not impose the strict size limit long assumed. Ecology, development, temperature and evolutionary history may also matter. The question is an active research debate.
Wingspan is not body mass
A wingspan near two-thirds of a metre sounds bird-sized, but it does not directly measure weight or strength. Fossil wings support estimates of overall scale; they cannot tell us exactly how the animal accelerated, turned or carried prey. Modern dragonflies are useful comparisons for flight, but griffinflies had different anatomy and lived in different air, vegetation and predator communities.
What happened to the giants?
Giant griffinflies did not vanish in one simple event with a single known cause. Insect diversity and body sizes changed through the Palaeozoic alongside shifts in climate, atmospheric composition, habitats and predator communities. The last occurrence in a rock record may reflect true extinction, incomplete sampling, or both. The Carboniferous coal swamps provide the ecological setting; fossils and physiological models continue to test how several factors combined.
Frequently asked questions
Was Meganeura a true dragonfly?
It was a giant dragonfly-like griffinfly in Meganisoptera, an extinct group distinct from modern dragonflies.
How wide were Meganeura’s wings?
Common estimates are roughly 65–70 centimetres, based on fossil wing material.
Did high oxygen alone cause insect gigantism?
No. Oxygen may have contributed, but its role is debated and other physiological and ecological factors matter.
Can fossils show how Meganeura hunted?
Anatomy and biomechanical comparisons support aerial predation, but exact hunting behaviour is inferred.