Abstract

Cockroaches are the dominant insects in Carboniferous terrestrial biotas, however, approximately 90% of specimens consist only of isolated wings or wing fragments. This bias has been attributed variously to decay and selective preservation, transport, predation, or collection. The state of preservation of Carboniferous cockroaches was documented in extensive collections from the Westphalian at Writhlington, U.K., where collection bias was minimal. The wings may be intact, or more usually fracture across the veins. Laboratory experiments were conducted on the genera Periplaneta and Blaberus to determine the effects of decay and transport following drowning. The decay experiments revealed a series of disarticulation stages that were reached more rapidly in specimens transported in a circular flume, particularly where some decay had occurred first. The wings detached from the body at a late stage, and separated to varying degrees along the veins, whether or not transport was involved. Experiments on isolated wings showed that breakage occurs across the veins. This pattern is more similar to that observed in the fossils than is the pattern induced by decay in water. The results were compared with observations on predation on these cockroaches and other insects by reptiles and arachnids. Vertebrates such as lizards are indiscriminate feeders and commonly bite through the wings. Arachnids with cheliceral teeth fragment the cuticle but may leave the wings intact. Predation by arachnids followed by breakage provides a more likely explanation than decay and selective preservation for the predominance of isolated wings in the fossil biota.

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