Phyloblatta

Phyloblatta is a genus of late Carboniferous insects placed among stem-group Dictyoptera, the evolutionary branch related to modern cockroaches, termites and mantises. It looked broadly cockroach-like, with a flattened body and veined wings, but it was not a living cockroach species. Most fossils assigned to the genus are forewing impressions, so the intricate vein network carries much of the taxonomic evidence.

The best-known species, P. gaudryi, comes from the famous Commentry fossil deposit in central France. Its holotype preserves both forewings, a hind wing and part of the thorax in connection, offering an unusual view of an individual insect. The more complete fossil sharpens the comparison, but it still does not reveal colour, diet or the full range of behaviour. Phyloblatta is included in the ancient arthropod catalogue.

Quick facts

A genus built from a changing fossil record

Anton Handlirsch established Phyloblatta in 1906. The species P. gaudryi had first been described by Agnus in 1903 from Commentry. That locality, in the Allier department of France, is known for abundant late Carboniferous plants and insects. Early authors assigned many wing impressions to broad “roachoid” groups; later work revised those identifications by comparing venation and the structure of the thorax when available.

The name does not refer to one completely known animal. Several species have been included over time, often on the basis of isolated forewings from Europe and North America. A wing can preserve a distinctive character combination, but a missing body makes it difficult to compare the specimen with relatives whose anatomy is better known. Some old assignments remain due for reassessment because the original material has not been redescribed with modern imaging.

Taxonomic statements should therefore distinguish the well-described holotype of P. gaudryi from the wider collection of species historically placed in the genus. The holotype is specimen MNHN.F.R51454 in the Muséum national d’Histoire naturelle, Paris. Its unusually connected wings make it central to discussions of the genus and of early dictyopteran evolution.

What the Commentry holotype preserves

The specimen is an exceptionally well-preserved negative imprint. It retains left and right forewings and a hind wing associated with part of the thorax. The wings lie close enough to one another that their arrangement can be reconstructed with more confidence than in isolated material. The fossil does not preserve a complete articulated skeleton, and it should not be described as an intact animal simply because several wings are connected.

The forewings show a network of branching veins between the media (M) and anterior cubitus (CuA), including evidence that branches of M fused with CuA. The arculus and the routes of the radial and cubital systems are also important in comparing dictyopteran wings. Researchers use these topological relationships, not just overall size or the brown colour of a modern illustration, to diagnose the fossil.

The hind wing has a broad anal region that differs from the narrower condition in many living cockroaches and some fossil roachoids. This combination of features is part of why P. gaudryi is treated as a stem dictyopteran rather than casually folded into a modern cockroach family. The evolutionary placement depends on a set of homologous wing characters and is revised as new fossils and comparative analyses become available.

Wing measurements and body size

The holotype’s hind wing is about 29.4 millimetres long. This is a direct measurement of one preserved wing, not the total length of the insect. The body is incomplete and wings can differ in length from the abdomen or from one another. A single value therefore cannot define the size range of the genus or provide a precise wingspan without additional measurements and assumptions about how the wings were held.

Many other specimens are isolated forewings, some incomplete or compressed. Their dimensions can still be compared, but estimates must account for broken apices, overlap and deformation. Wing venation may spread or distort during fossilization; a dark boundary in an impression may be a vein, a fold or a crack. Researchers compare both sides of a wing where possible and inspect the fossil under varied lighting or imaging methods.

The better-preserved holotype improves anatomical confidence, while the isolated specimens expand the record of variation. It does not solve every question about sexual dimorphism, growth or species boundaries. No series of juvenile and adult bodies is known well enough to reconstruct development through the full life cycle of Phyloblatta.

Living relatives and what remains inference

A flattened body, large forewings and long antennae are consistent with a broad cockroach-like appearance. Modern cockroaches can help palaeontologists understand how a dictyopteran might fold its wings or use appendages, but they are not exact behavioral models for a Pennsylvanian stem taxon. The evolutionary lineage leading to living cockroaches also includes many extinct forms with different anatomical combinations.

The Commentry fossil does not preserve gut contents, mouthpart wear, a feeding trace or eggs attributable to Phyloblatta. It is therefore not possible to call the genus exclusively predatory, herbivorous or omnivorous from the holotype. The humid coal-forest setting is supported by the deposit and its fossil plants, but a forest floor in an illustration is a habitat reconstruction rather than the exact place where this individual died.

Two pairs of veined wings support flight capability, but the details of take-off, flight height and daily activity are not directly observed. The antennae probably sensed the surroundings, as in many insects, yet their sensory performance and the animal’s eyesight are not preserved. These distinctions keep a vivid reconstruction from being mistaken for a fossil photograph.

Reading the veins rather than the silhouette

The forewing’s branching system is the most dependable diagnostic evidence. The relative course and branching of R, M, CuA and other veins can separate groups whose overall outline seems similar. Cross-vein density and the way the anal region is built also matter. A well-preserved wing may reveal relationships that cannot be inferred from the insect’s general cockroach-like shape.

This is why a fossil image should show the wing network clearly and avoid borrowing distinctive features from a modern species. Body colour, precise wing position and fine soft anatomy remain artistic choices. The related giant griffinfly Meganeura and millipede Arthropleura belong to the same broad Carboniferous world but are not close relatives of Phyloblatta. Their comparison is useful for understanding the diversity of ancient arthropods, not for filling in missing details of this insect.