"Roachoids",[1] also known as "Roachids", "Blattoids"[2] orEoblattodea,[3] are members of thestem group ofDictyoptera (the group containing moderncockroaches,termites andpraying mantises). They generally resemble cockroaches, but most members, unlike modern dictyopterans, have generally long externalovipositors, and are thought not to have laidootheca like modern dictyopterans.
Cockroaches are popularly thought to be an ancient order ofinsects, with their origins in theCarboniferous.[4] However, since the middle of the 20th century it has been known that the primitive cockroach insects found fossilized inPalaeozoic strata are the forerunners not only of modern cockroaches and termites but also ofmantises.[5] The origin of these groups from a blattopteran stock are now generally thought to be in the EarlyJurassic; the earliest modern cockroaches appeared during theLate Jurassic.[6] Thus, the “Palaeozoic cockroaches” are not cockroaches per se, but aparaphyletic assemblage of primitive relatives.[7] The youngest known roachoids date to the Cretaceous, by which time they were rare compared to modern cockroaches.[8]
The fossils assigned to the "roachoids" are of general cockroach-like build, with a large disc-likepronotum covering most of the head, longantennae, legs built for running, flattened body and heavily veined wings with the distinct arched CuP-vein so typical of modern cockroach wings.[9] Like modern cockroaches, the roachids were probably swift litter inhabitants living on a wide range of dead plant and animal matter.
Contrary to modern forms, female roachoids all have a well-developed externalovipositor. They probably inserted eggs into substrate. The egg pods, calledootheca, seen in modern dictyopterans is a new shared trait (synapomorphy) separating them from their primitive ancestors.[10] Some of the roachoid species could reach relatively large sizes compared to most of their modern relatives, likeProgonoblattina[11][12] andNecymylacris[13][14] fromCarboniferous reach around 9 centimetres (3+1⁄2 in) in total length, and the largestOpsiomylacris having wings reaching 7.5 centimetres (3 in), close to modern largest cockroachMegaloblatta longipennis.[12]
^Guthrie, D. M. & A. R. Tindal (1968): The Biology of the Cockroach. St. Martin's Press, New York
^Grimaldi, D (1997): A fossil mantis (Insecta: Mantoidea) in Cretaceous amber of New Jersey, with comments on early history of Dictyoptera.American Museum Novitates 3204: 1–11
^Vršanský, P.; Palková, H.; Vršanská, L.; Koubová, I.; Hinkelman, J. (2022). "Mesozoic origin-delayed explosive radiation of the cockroach family Corydiidae Saussure, 1864".Biologia.78 (6):1627–1658.doi:10.1007/s11756-022-01279-1.S2CID254479766.
^Grimaldi, D. & M. S. Engel, Michael (2005): Evolution of the Insects, Cambridge University Press,ISBN0-521-82149-5
^Schneider, J. (1983): Die Blattodea (Insecta) des Paleozoicums, Teil II, Morphogenese des Flügelstrukturen und Phylogenie.Freiberger Forchnungshefte, Reie C 391. pp 5-34
