The Early History of Giant Cockroaches: Gyroblattids and Necymylacrids (Blattodea) of the Late Carboniferous

Large-winged blattoids of the Middle to Late Pennsylvanian reveal a striking appearance, diversification, and decline in the fossil record. Among them, the families Necymylacridae Durden, 1969, and Gyroblattidae Durden, 1969, as well as the mylacrid genus Opsiomylacris exhibit, the largest pre-Cenozoic blattoids with forewing lengths up to 7.5 cm. As finds from coal-bearing sedimentary basins in Europe, North Africa, and North America indicate, these giant insects started to spread around the Bashkirian-Moscovian transition and experienced a diversification in late Moscovian and Kasimovian times, until they disappeared in the middle Gzhelian. Whereas necymylacrids are only patchily reported and still lack distributional patterns, we disclose the occurrence and particular habitat preference of gyroblattids. Although appearing first in some vast North American basins, they became successively widespread only in small-sized basins of the European Variscan interior. Frequently found associated with enigmatic gymnosperms, they may have lived in well-drained hinterland areas from where they immigrated into the ever-wet basin centers only with increasing seasonality. Gyroblattids apparently followed meso- to xerophilous plants and likely colonized spaces offering a broader spectrum of edaphic conditions that resulted from the closeness of erosional and depositional areas. The presented analysis and revision of all gyroblattids aim to facilitate future more realistic biodiversity estimations based on fossil taxa.