The Stone Mantis

Lithomantis carbonarius, as illustrated by Woodward (1876).

In 1876, Henry Woodward published the description of a large fossil insect found in a Scottish clay-ironstone nodule. This insect, when alive, would have had a wingspan of well over ten centimetres: Woodward measured the longest preserved wing at two and a quarter inches long, and a sizeable piece of the end was still missing. Believing it to be an ancient relative of the modern mantids, he named it Lithomantis carbonarius, the 'stone mantis from a coal measure'. Woodward's interpretation of his new fossil was to prove incorrect: it was not a mantis, but a member of those spectacular wonders of the Palaeozoic, the palaeodictyopteroids. More specifically, Lithomantis has been placed in a group of palaeodictyopteroids distinguished by Sinitshenkova (2002) as the Eugereonoidea.

Reconstructed wings of Lycocercus goldenbergi from Kukalová (1969), showing the overlap between the fore and hind wings; note also the bold colour patterning (often preserved in insect wings).

The palaeodictyopteroids are a group long overdue a truly comprehensive revision, and many aspects of their higher classification remain debatable. Of the current default classification, that of Sinitshenkova (2002), Prokop & Nel (2004) somewhat snarkily commented that, "Sinitshenkova’s classification cannot be considered based on the cladistic method, even if it uses the cladistic terminology". Nevertheless, Sinitshenkova defined the Eugereonoidea by a number of wing characters: wings that were about 2.5 times as long as broad, a subcostal vein reaching the costal vein near the wing apex, medial and cubital veins with little-branched anterior forks but much-branched posterior forks, and a tendency for the archedictyon (the net-like array of veinlets running amongst the major wing veins in palaeodictyopteroids) to become simplified or replaced by direct cross-veins. Members of the Eugereonoidea are known from the Upper Carboniferous and Lower Permian (Sinitshenkova 2002; Prokop & Nel 2007) and, like other palaeodictyopteroids, would have inhabited tropical latitudes in life.

Wings of the eugereonid Peromaptera filholi, from Kukalová (1969).

Like other palaeodictyopteroids (and, indeed, many other Palaeozoic insect groups in general), Eugereonoidea are mostly known from fossils of the wings, but those that are more completely known are large-bodied insects with relatively long sucking beaks. One species, Eugereon boeckingi, had a beak over three centimetres long; that of Lithomantis was a bit more restrained at only just over one centimetre. They used these impressive weapons to attack the stems of the ferns and seed ferns of the time in search of sap. Other palaeodictyopteroids, including the eugereonoid Lycocercus goldenbergi (Kukalová 1969), had much shorter beaks, and would have probably fed from spores or seeds. Eugereonoids had fairly broad-based wings with the fore and hind pairs of wings originally little differing from each other. The pronotum bore well-developed paranotal lobes that have lead to descriptions of these insects as 'six-winged'; though the pronotal lobes could not actively flap in the manner of true wings, Wootton & Kukalová-Peck (2000) suggested that they were somewhat movable, and could have been used to stabilised pitch. In the family Lycocercidae, the two pairs of wings overlapped to a degree unknown in any living insects; in Notorhachis wolfforum, the forewings overlapped the hind wings almost entirely. As argued by Wootton & Kukalová-Peck (2000), these species would have flown quickly but with relatively little manouevrability, like insectoid turkeys. In contrast, members of the families Eugereonidae and Megaptilidae developed relatively long narrow forewings followed by shorter, broader hind wings. Like modern insects with comparable wing morphologies (such as bees and butterflies), members of these families probably beat the two pairs of wings in concert, and would have been more manoeuvrable compared to the lycocercids. However, with an estimated wingspan of over a foot, the eugereonoid Megaptilus blanchardi was by far the largest insect ever known to develop this mode of flying.

REFERENCES

Kukalová, J. 1969. Revisional study of the order Palaeodictyoptera in the Upper Carboniferous shales of Commentry, France part II. Psyche 76: 439-486.

Prokop, J., & A. Nel. 2004. A new genus and species of Homoiopteridae from the Upper Carboniferous of the Intra-Sudetic Basin, Czech Republic (Insecta: Palaeodictyoptera). European Journal of Entomology 101: 583-589.

Prokop, J., & A. Nel. 2007. New significant fossil insects from the Upper Carboniferous of Ningxia in northern China (Palaeodictyoptera, Archaeorthoptera). European Journal of Entomology 104: 267-275.

Sinitshenkova, N. D. 2002. Superorder Dictyoneuridea Handlirsch, 1906 (=Palaeodictyopteroidea). In History of Insects (A. P. Rasnitsyn & D. L. J. Quicke, eds) pp. 115-124. Kluwer Academic Publishers: Dordrecht.

Woodward, H. 1876. On a remarkable fossil orthopterous insect from the coal-measures of Scotland. Quarterly Journal of the Geological Society of London 32: 60-65.

Wootton, R. J., & J. Kukalová-Peck. 2000. Flight adaptations in Palaeozoic Palaeoptera (Insecta). Biol. Rev. 75: 129-167.