Roachoid Explained

"Roachoids",^[1] also known as "Roachids", "Blattoids"^[2] or Eoblattodea,^[3] are members of the stem group of Dictyoptera (the group containing modern cockroaches, termites and praying mantises). They generally resemble cockroaches, but most members, unlike modern dictyopterans, have generally long external ovipositors, and are thought not to have laid ootheca like modern dictyopterans.

Systematic position

Cockroaches are popularly thought to be an ancient order of insects, with their origins in the Carboniferous.^[4] However, since the middle of the 20th century it has been known that the primitive cockroach insects found fossilized in Palaeozoic strata are the forerunners not only of modern cockroaches and termites but also of mantises.^[5] The origin of these groups from a blattopteran stock are now generally thought to be in the Early Jurassic; the earliest modern cockroaches appeared during the Early Cretaceous.^[6] Thus the “Palaeozoic cockroaches” are not cockroaches per se, but a paraphyletic assemblage of primitive relatives.^[7] The youngest known roachoids date to the Cretaceous, by which time they were rare compared to modern cockroaches.^[8]

Anatomy and habits

The fossils assigned to the "roachoids" are of general cockroach-like build, with a large disc-like pronotum covering most of the head, long antennae, 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 external ovipositor. They probably inserted eggs into substrate. The egg pods, called ootheca, 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, like Progonoblattina^[11] and Necymylacris^{[12] [13]} from Carboniferous reach around 9cm (04inches) in total length, and the largest Opsiomylacris having wings reaching 7.5cm (03inches), close to modern largest cockroach Megaloblatta longipennis.^[14]

See also

• Archimylacris

Notes and References

1. Correia . Pedro . Pereira . Sofia . Cavaleiro . Marco . Correia . Miguel . Sá . Artur A. . Nel . André . 2022-02-06 . The first poroblattinid roachoid from the uppermost Carboniferous of Portugal . Historical Biology . 35 . 2 . 242–248 . 10.1080/08912963.2022.2032030 . 246664148 . 0891-2963.
2. Haug . J.T. . Leipner . A. . Wappler . T. . Haug . C. . 2013-10-31 . Palaeozoic insect nymphs: new finds from the Piesberg quarry (Upper Carboniferous, Germany) . Bulletin of Geosciences . 779–791 . 10.3140/bull.geosci.1401 . 1802-8225. free .
3. Li . Xinran . 2019-08-30 . Disambiguating the scientific names of cockroaches . Palaeoentomology . 2 . 4 . 390–402 . 10.11646/palaeoentomology.2.4.13 . 202789239 . 2624-2834.
4. Guthrie, D. M. & A. R. Tindal (1968): The Biology of the Cockroach. St. Martin's Press, New York
5. 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
6. Hinkelman . Jan . July 2019 . Spinaeblattina myanmarensis gen. et sp. nov. and Blattoothecichnus argenteus ichnogen. et ichnosp. nov. (both Mesoblattinidae) from mid-Cretaceous Myanmar amber . Cretaceous Research . en . 99 . 229–239 . 10.1016/j.cretres.2019.02.026. 134700289 .
7. Grimaldi, D. & M. S. Engel, Michael (2005): Evolution of the Insects, Cambridge University Press,
8. Li . Xin-Ran . Huang . Di-Ying . 2023-03-29 . Atypical 'long-tailed' cockroaches arose during Cretaceous in response to angiosperm terrestrial revolution . PeerJ . en . 11 . e15067 . 10.7717/peerj.15067 . 2167-8359 . 10066690 . 37013144 . free .
9. Schneider, J. (1983): Die Blattodea (Insecta) des Paleozoicums, Teil II, Morphogenese des Flügelstrukturen und Phylogenie. Freiberger Forchnungshefte, Reie C 391. pp 5-34
10. Hörnig . Marie . Haug . Carolin . Schneider . Jörg . Haug . Joachim . 2018 . Evolution of reproductive strategies in dictyopteran insects – clues from ovipositor morphology of extinct roachoids . Acta Palaeontologica Polonica . 63 . 10.4202/app.00324.2016 . 0567-7920. free .
11. Sellards. Elias Howard. 1903-04-01. Some new structural characters of Paleozoic cockroaches. American Journal of Science. en. s4-15. 88. 307–315. 10.2475/ajs.s4-15.88.307. 1903AmJS...15..307S. 0002-9599.
12. Stratigraphy and paleontology of Cemetery Hill (Desmoinesian-Missourian: Upper Carboniferous), Columbiana County, eastern Ohio. The Ohio State University. 2004. en. Cary Ray. Easterday.
13. Schneider. Joerg. Scholze. Frank. Germann. Sebastian. Lucas. Spencer. 2021-04-16. THE LATE PENNSYLVANIAN NEARSHORE INSECT FAUNA OF THE KINNEY BRICK QUARRY INVERTEBRATE AND VERTEBRATE FOSSIL LAGERSTÄTTE, NEW MEXICO. Bulletin of the American Museum of Natural History. 84.
14. Schneider . Joerg W. . Rößler . Ronny . 2023 . The Early History of Giant Cockroaches: Gyroblattids and Necymylacrids (Blattodea) of the Late Carboniferous . Diversity . en . 15 . 3 . 429 . 10.3390/d15030429 . 1424-2818 . free .