Fossilized insects, unfortunately, do not often diverge dramatically from modern ones: it seems that once a body-plan evolves among them it is never lost, and if its exponents die out utterly it will likely be recapitulated later on by an unrelated lineage. The notorious griffinflies (order Meganisoptera) that patrolled Earth's skies for 67 million years, including the 28-in.wingspan Meganeuropsis, were essentially hawk-sized dragonflies (a taxonomic oversimplification but an ecological truth); the various members of the superorder Dictyoptera (cockroaches, mantids and termites), both living and dead, are more or less Variations on the Theme of "I Am a Roach"–e.g., We Are Roaches With Sclerotized Forewings (Umenocoleidae), We Are Carnivorous Mantis-Like Roaches (Raphidiomimidae), I Am a Roach With Earwig-esque Cerci With Which I Probably Clasped My Mate (Fuzia), and I Am a Roach With Leaping Hind Legs and a Name Like That of a Romulan (Skok).
Thankfully, there are exceptions. The Kalligrammatidae were fluttering, colorful pollinators often termed "the butterflies of the Mesozoic"...but they were close kin of antlions (which they hardly resembled), and are only distant cousins of their extant namesakes. And, of course, there were the Chresmodidae (Handlirsch, 1906), which are what I am posting about, although it may be hard to tell that from what I have written so far.
No, it appears that Chresmoda sp. owe their gigantism to a unique aspect of their tarsi: namely, the fact that said tarsi were unreservedly flagellate, the 2 foremost tarsomeres (the segments which comprise an insect's foot) being subdivided into an excess of 40 tiny articles in what was apparently a means of spreading weight. Why does this warrant italicization? Well, the foundational morphology from which all insects descend has no more than 5 podites: numerous lineages among the Insecta have less than that, but never more, with the strange exception of Chresmoda.
In search of an explanation for the sinuous feet of the Chresmodidae we venture into the wily realm of developmental genetics. Possibly, a gene regulating segment multiplication in the antennae shifted to the legs, which, these limbs being serially homologous, is not implausible; or perhaps the gene responsible for tarsomere arrangement simply went overboard with the apical podites ("over-expression"). However, additional mutations in unrelated parts of the genome–specifically, those parts dealing with tarsal musculature–would be necessary in order for the newly super-multiarticulate feet to function. This could explain why this route for dealing with supporting one's weight on fluid occurred only once in the insects; but however it appeared, the chresmodids were certainly successful in their own time, living for at least 80 mya (Aalenian-Cenomanian Epochs) at both ends of Eurasia and in South America.
In the 173 years chresmodids have been known their taxonomy has been a source of prolonged debate and confusion. Ernst Friedrich Germar, author of the name Chresmoda, initiated the mess when he attributed that moniker to a colleague despite the work in the descriptive monograph being clearly his own; numerous species–Pygolampis gigantea (Germar, 1839), Propygolampis bronni (Weyenbergh, 1874), Saurophthirodes mongolicus (Ponomarenko, 1986), Sternarthron zitteli (Haase, 1890), Gryllidium oweni (Westwood, 1854)–and the genus Halometra (Oppenheim, 1888) were synonymized with the type (C. obscura) over the years, often being initially classified in a separate order from their senior synonym: indeed, the poorly preserved S. zitteli was frequently classified as an arachnid, and even compared to the bizarre sea spiders (class Pycnogonida) in what was probably an instance of systematist's desperation (akin to writer's block).
By far the most frequent ordinal attribution (if any) for Chresmodidae, however, is the Phasmatodea, or stick and leaf insects. Aleksandr G. Sharov even went so far as to include the living Phyllidae (leaf insects) in the superfamily Chresmodoidea. Unfortunately, the phylogeny of the Phasmatodea is, for lack of a better word, unclear; one predominant school of thought regards them as the sister-group of the Orthoptera (grasshoppers, crickets, etc.): the other, as close kin of the Embioptera, an obscure order of subsocial insects known in the vernacular as webspinners: the former view is supported by morphology; the latter, genetics. Orthopterans and embiopterans are so dissimilar that there appears to be little opportunity for compromise. Another view holds that extant Phasmatodea are not even monophyletic, with the oddball Timematidae being more closely related to Notoptera (icecrawlers and rockcrawlers) than to the remainder of the living species (Euphasmida).
If so, then I must say that they are weird stick insects. Well, I'm off.
[Sadly, inclusion of pictures in this post is more trouble than it's worth. You can find excellent photographs of chresmodid fossils in Delclòs et al., 2008.]
Andersen, N. M. (1982). The Semiaquatic Bugs (Hemiptera: Gerromorpha): Phylogeny, Adaptations, Biogeography and Classification. Klampenborg: Scandinavian Science Press.
Delclòs, X., Nel, A.; Azar, D.; Bechly, G.; Dunlop, J. A.; Engel, M. S. & Heads, S. W. (2008). The enigmatic Mesozoic insect taxon Chresmodidae (Polyneoptera): new paleobiologicalN. Jb. Palaeont. Abh., 247(3), 353-381.
Nel, A.; Marchal-Papier, F.; Béthoux, O. & Gall, J. C. (2004). A new "stick-insect like" from the Triassic of the Vosges (France) ("pre-Tertiary Phasmatodea") [electronic version]. Annals of the Entomological Society of France, 40(1), 31-36.
Nel, A. & Delfosse, E. (2011). A new Chinese Mesozoic stick insect [electronic version]. Acta Palaeontologica Polonica, 56(2), 429-432.