Discovery of the Earliest Winged Insects from the Carboniferous: A New Megasecopteran Species and the Ecology of Paleozoic Insects

A dry and desolate plateau in modern Argentina once formed part of a dynamic ancient basin more than 320 million years ago. During that time, rivers, lakes, and glaciers alternated across the landscape. This region, known today as the Paganzo Basin, accumulated sedimentary deposits reaching a thickness of nearly 4,500 meters and preserves geological records of rhythmic glacial and interglacial cycles during the Late Paleozoic ice age.

Within the lowermost unit of this basin, the Guandacol Formation, palaeontologists discovered an exceptionally valuable fossil: one of the earliest known winged insects in the world. Fossils of winged insects from the Mississippian (early Carboniferous) are extraordinarily rare. So far, only two confirmed localities have yielded such remains: Delitzsch in Germany and Guandacol in La Rioja Province, Argentina. Absolute dating of the Guandacol strata indicates an age of about 326 million years, placing the fossils in the Serpukhovian stage of the Carboniferous.

Paganzo Basin（Image source：Fernandez JA et al. (2024)， CC BY 4.0 ）

Among the material collected from this site, researchers identified a previously unknown species of the order Megasecoptera, named Xenoptera latigra. The fossil is preserved with remarkable clarity, displaying three-dimensional wing venation that allows individual veins to be traced in detail, including their branching patterns, directions, and fusion zones. Such preservation provides rare insight into the early evolution of insect wings.

Members of the family Xenopteraidae typically share several distinctive wing features: a relatively large basal cell near the wing base, a fusion between the posterior radius (RP) and the anterior media (MA), and a broad costal region along the leading edge of the wing. The new species displays all of these characteristics but also possesses several unique traits. For instance, the main branch of the posterior radius continues as a relatively long straight segment after separating from the anterior media. In addition, three to four crossveins occur between the principal veins, whereas related species usually show only one or two. The overall venation pattern is also more widely spaced rather than tightly packed. These differences clearly distinguish the fossil as a new species.

Possible reconstruction of a megasecopteran insect. (a) and (d) represent adults（Image source：Jakub Prokop et al.， CC BY 4.0 ）

The preserved wing is interpreted as a hindwing. In Megasecoptera, forewings and hindwings appear similar in overall shape, yet hindwings typically possess a larger basal cell, a longer posterior radius, and a slightly convex posterior margin near the base. All of these traits are present in the specimen.

This discovery also connects the Guandacol Formation with another fossil locality in the same basin: La Cuestita de la Herradura in the Malanzán Formation, approximately 240 kilometers away. Although the Malanzán Formation has not yet been dated radiometrically, both sites contain related insect groups, including members of Eugeropteridae and the genus Xenoptera. Their shared taxa suggest that the two localities formed under similar environmental conditions and likely accumulated sediments during comparable time intervals.

The Guandacol locality contains more than just this newly described insect. Earlier research had already documented three species belonging to the superorder Odonatoptera, representing three different evolutionary lineages: Eugeroptera, Kukaloptera, and Argentinoptera. These insects were probably predatory, much like their modern relatives among dragonflies and damselflies. In contrast, Megasecoptera such as Xenoptera latigra were herbivorous insects equipped with beak-like mouthparts used to pierce plant tissues and suck fluids.

The coexistence of these two ecological guilds—predators and plant-feeding insects—indicates that the Guandacol ecosystem supported a complex early insect community. Such communities likely occupied diverse ecological roles within Carboniferous terrestrial environments.

Because the fossil wing was found in continental sedimentary deposits, the adult insects probably lived in habitats close to land. However, many early relatives of dragonflies are thought to have had aquatic juvenile stages. Evidence from both fossil and living species suggests that the larvae of Odonatoptera were already aquatic during the Paleozoic, and all known later records from the Mesozoic and Cenozoic show similar water-dwelling nymphs. Although no larval fossils have yet been discovered at Guandacol, the sedimentary context strongly suggests the presence of aquatic habitats capable of supporting such life stages.

Megasecoptera have traditionally been considered fully terrestrial insects throughout their life cycle. However, recent reassessments of Paleozoic insect larvae suggest that some members of the broader palaeodictyopteroid group may have had more complex developmental strategies, possibly including amphibious or aquatic immature stages. For the genus Xenoptera, the available fossil evidence indicates that adults were terrestrial. Yet because no larval specimens have been found, it remains uncertain whether the juveniles might also have interacted with aquatic environments.

This uncertainty makes the Guandacol insect assemblage particularly valuable for understanding the early evolution of insect life histories. The fossils not only provide evidence for some of the earliest winged insects on Earth, but also reveal an ecosystem where plant-feeding and predatory insects already formed an interconnected community. Each new discovery from these deposits adds another piece to the puzzle of how insects first diversified and adapted to the landscapes of the Paleozoic world.

Author: Shui-Ye You

References:

1. Fernandez JA et al. (2024). Coniferophytes from the Bajo de Veliz Formation (Gzhelian-Asselian), San Luis Province, Argentina. Acta Palaeobotanica.

2. Petrulevičius JF and Gutiérrez PR. (2025). Oldest winged insects: first Megasecoptera from the early Carboniferous (Serpukhovian) of Argentina. Palaeontology.

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