"Roachoids", also known as "Roachids" or "Blattoids" are members of the

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

Dictyoptera Dictyoptera (from Greek δίκτυον ''diktyon'' "net" and πτερόν ''pteron'' "wing") is an insect superorder that includes two extant orders of polyneopterous insects: the order Blattodea (termites and cockroaches together) and the o ...

(the group containing modern

cockroach Cockroaches (or roaches) are a Paraphyly, paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are we ...

es,

termite Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blatto ...

s 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 An ootheca (pl. ''oothecae'' ) is a type of egg mass made by any member of a variety of species including mollusks (such as ''Turbinella laevigata''), mantises, and cockroaches. The word is a Latinized combination of ''oo-'', meaning "egg", f ...

like modern dictyopterans.

Systematic position

Cockroaches are popularly thought to be an ancient order of

insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...

, with their origins in the Carboniferous. 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

mantis Mantises are an order (Mantodea) of insects that contains over 2,400 species in about 460 genera in 33 families. The largest family is the Mantidae ("mantids"). Mantises are distributed worldwide in temperate and tropical habitats. They ha ...

es.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 The origin of these groups from a blattopteran stock are now generally thought to be in the Early

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

; the earliest modern cockroaches appeared during the Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. Thus the “Palaeozoic cockroaches” are not cockroaches per se, but a paraphyletic assemblage of primitive relatives.

Anatomy and habits

The fossils assigned to the "roachoids" are of general cockroach-like build, with a large disc-like

pronotum The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum ( dorsal), the prosternum (ventral), and the propleuron (lateral) on e ...

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. 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

, seen in modern dictyopterans is a new shared trait (

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

) separating them from their primitive ancestors. Some of the roachoid species could reach relatively large sizes compared to most of their modern relatives, like ''Archoblattina'' ''beecheri'' and '' Necymylacris'' (or '' Xenoblatta'') ''scudderi'' from Carboniferous reach around in total length, close to modern largest cockroach ''

Megaloblatta longipennis ''Megaloblatta longipennis'' is a species of cockroach in the family Ectobiidae Ectobiidae (formerly Blattellidae) is a family of the order Blattodea (cockroaches). This family contains many of the smaller common household pest cockroaches, amon ...

''.

References

{{Taxonbar, from=Q4925531 Extinct insect orders Prehistoric insects Carboniferous first appearances Lopingian extinctions Paraphyletic groups