This is Mazon Monday post #46. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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This week, as part of our series on Mazon Creek insects, we are looking at roaches, or to be more correct roachoids, as true roaches don't show up in the fossil record until the late Jurassic. Roachoids are the most common order of insects found in the Mazon Creek biota. At one point, Dr. Eugene Richardson listed 26 genera and 37 species. Unfortunately, while they might represent a large part of the insect diversity, the Blattidae are quite rare. They have been found in Pit 11 and the most terrestrial deposits. Personally, I know of a nice one from Pit 2 that ended up in the Smithsonian.
Roachoids were covered in Creature Corner by Andy Hay in June 1984.
Pit 11 Cockroaches
Cockroaches, Order Blattaria, constitute 60 to 70% of all insects found in the Pennsylvanian strata. "The age of Cockroaches" as many would dub the Pennsylvanian Period, was the result of warm, moist conditions prevailing at that time, ideal for their proliferation. In fact, the late Dr. Richardson listed 26 Genera and 37 Species of Blattidae discovered in the Mazon Creek Area alone. Statistics aside, Blattoids are not common in the nodules of the Francis Creek Shale. Concretion collectors have to remain alert, mimicry is not a modern trait in the insect world. The wings of several species of Blattoids resemble seed fern leaflets even to the venation. In other respects, the differences between Mazon Creek fossil specimens and those living today is extremely slight.
Jack Wittry has a few pages on Roachoids in the "The Mazon Creek Fossil Fauna" with some excellent pictures.
True cockroaches do not appear in the fossil record until the Late Mesozoic. The Carboniferous forms lacked the ability to produce egg sacs as do their modern counterparts. They laid eggs directly into the soil. This primitive group is now known collectively as Roachoids.
The majority of all known Carboniferous fossil insects are roachoids, though they are not common in the Mazon Creek Fauna, and are now believed to represent far fewer species than in the past. About 90 percent of all fossil roachoids consist of isolated wings or wing fragments. In fossils preserving the entire organism, visibility of the legs, lower wings, and body core is obscured by the upper wings. Also, studies have shown considerable variation in wing venation among groups. It is generally recognized that too much emphasis has been placed on slight differences in venation, resulting in far too many families and genera. The systematics of this group are in great need of revision.
Roachoids (Phylloblattidae) have the forewings modified into leathery or thickened protective coverings. Richly branching forewings of these Carboniferous roachoids bear a strong resemblance to fern pinnules-a feature early researchers declared to be a protective device (mimicry)-affording the owners some protection from predators. Researchers today dispute this. They feel that both pinnule and wing are thin and large-surfaced, thus requiring analogous structures (veins) for support. Present-day roaches are found living within leaf litter, likely the way their ancestors did 307 million years ago.
"The Richardson's Guide to the Fossil Fauna of Mazon Creek" has a nice drawing of cockroach nymphs in an article by Jarmila Kukalova-Peck
Neoptera with metamorphosis. Nymphs of cock- roaches had their wings enclosed in hardened cases and fused with the dorsal skeleton, resembling the thoracic shield side lobe of crustaceans, as do the nymphal wings of all present-day in- sects. A metamorphic instar was needed to return the wings to a working condition. A Blattoidea, nymph, FMNH PE 218827; dor sal view. B Nymph, Mary Helmus-Smith collection; ventral view. Scale bar = 10 mm (estimate).
Back in 2012, a roachoid was sold in the ESCONI show auction along with a 3 Tully Monsters!
