This is Mazon Monday post #45. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Gerarus constrictus, reconstruction by Burnham (1983); modified after Shabica and Hay (1997).
The gerarids are large winged insects from the Carboniferous Period. Fossils of gerarids have been found in deposits from Mazon Creek and Commentry, France. The animals are known for a distinctive stalked head. Some have spikes on their thorax. They are thought to be related to the ancestors of crickets and grasshoppers and have been placed in Order Protoorthoptera.
Gerarus was first described by Samuel H. Scudder in 1885. Scudder was an American entomologist and paleontologist in the late 1800's and early 1900's. He was an absolute giant in the study of fossil insects. A prolific writer, he was the authority on butterflies (Lepidoptera) and grasshoppers (Orthoptera) during his lifetime.
There's a good write up in the Creature Corner book about gerarids. The article first appeared in the ESCONI newsletter in April 1988.
Gerarids (insect)
Gerarids, Family Geraridae, were first described by Scudder in 1885 from several Mazon Creek specimens and are placed in the Order Paleodictyoptera. Later workers transferred them to the Order Protorthoptera. Protorthoptera first appear in the strata of the Lower Pennsylvanian. This order had a highly diverse body plan, with noticeable variations in the same species. Some specimens show a remarkable difference in venation of the right and left side wings. Characteristics such as these had early workers proclaiming each new specimen to be a new species.
Gerarids are readily distinguished by the elongated prothorax (neck-like extension), a feature of the Mantids and "walking sticks" of today. All Geraridae thus far described are from the Mazon Creek area and Commentry, France. Mazon Creek strata is 5 to 10 million years older than Commentry. In an attempt to explain the presence of these insects at localities seemingly so distant, one must look at the paleogeography of that Period. Europe, Africa and North America had "bumped" together, forming a pre-Appalachian Mountain chain, and aligning Europe and North America so that present day France and Illinois were on the Equator. A good analogy of that climate would be to place the Congo and Amazon forests side by side.
Gerarids are classed as Insecta; Order Protorthoptera; Family Geraridae; Genus Gerarus collaris,danielsi,vetus, plus bruesi and fischeri. Anepitedius giraffa. Gerarulus radialis. Genentomium validum. Progenentomum carbonis. Nacekomia rossae. It is to be noted that all except G. bruesi and G. fischeri are from Mazon Creek. The next concretion might well change the list dramatically. Several species are known only from a fragment. It is in a spirit of let well enough alone until further discoveries are made that the list stands.
Characteristics - All four wings are similar in size, but variable in wing venation. Wings are folded over the back, an orthropterid attribute. A distinctive characteristic is their extended prothorax. Some species, most notably G. danielsi, had the prothorax protected by stout spines, a protective device utilized by other invertebrates, fish, reptiles, mammals, and plants. The head generally is small. Antennae are long and threadlike. Legs are well developed for running. These characteristics cover all genera of the Geraridae. Gerarus is usually larger than the other genera listed. identification down to the species level is a task for the specialist. Gerarids are considered to have been plant eaters and good flyers, well adapted to the moist, tropical Carboniferous landscape. At the close of the Permian the climate changed. Arid conditions and the disappearance of the lush vegetation saw the demise of the Geraridae.
- Andrew A. Hay
The Mazon Creek Fossil Fauna has a few pages on gerarids, including some very nice pictures.
The family Geraridae was first described by Scudder in 1885, He originally placed them in the Order Protorthoptera, but even today the exact affinities of Gerarus still await elucidation. It is generally agreed that gerarids are somehow related to the ancestors of crickets and grasshoppers. Like them, Gerarus was probably not a very active flier. Instead, it would have clambered on vegetation similar to a stick insect, relying primarily on its spines to dissuade potential predators. If that wasn't enough, it could escape by jumping and using its wings primarily for gliding.
Some specimens show a difference in the venation of the left and right side wings. Characteristics such as these had early researchers proclaiming each new specimen to be a new species. Many of the names are now synonymous (see Mazon Creek Fauna Taxonomy List, page 176). Geraridae presently includes the fol- lowing taxa: Gerarus constrictus, G. collaris, G. vetus, danae, G danae, G. mazonus, Anepitedius giraffa, Genentomium validum, and Progenentomun carbonis. This family has the following characteristics:(a) all four wings similar in size and folded over the back; (b) extended prothorax, with some species having a collar of stout spines; and (c) antennae long and thread-like.The overall length of some species-tip of wing to anterior tip of prothorax-is 75 mm. Identification to the species level is a task best left for a specialist.
