BEETLE BURROWS WITH A TERMINAL CHAMBER: A CONTRIBUTION TO THE KNOWLEDGE OF THE TRACE FOSSIL MACANOPSIS IN CONTINENTAL SEDIMENTS

Abstract

Domichnial and domichnial-fodinichnial burrows of ground beetles (Coleoptera: Carabidae) belonging to the genera Bembidion and Harpalus, respectively, and pupichnial burrows of Melolontha (Coleoptera: Melolonthinae: Scarabaeidae) occur in sandy to muddy nonvegetated or partly vegetated substrate on a well-drained, rarely flooded alluvial plain of the Dunajec River (Sandomierz Basin, southern Poland). The burrows show a characteristic morphology, with a straight or curved shaft and a horizontal to oblique terminal chamber. The Bembidion and Harpalus burrows are similar and show a wide range of morphological variability, including forms in which the terminal chamber is poorly outlined. Their inclination changes from oblique (most common) on horizontal surfaces to horizontal in steep scarps. The Melolontha burrows are larger, with vertical shafts and strongly elongated chambers. The Melolontha and Harpalus burrows occupy vegetated areas in more distal areas, the Bembidion stephensii burrows occur in the intermediate environments with respect to the river channel, while the B. quadrimaculatum is present in more proximal, nonvegetated or poorly vegetated flood plain and scarps of the river channel. Comparison with the trace fossil Macanopsis indicates that ground beetles and scarab beetles should be included as possible tracemakers (as well as spiders, wasps, or millipedes as presented in the literature) of Macanopsis in continental settings. These traces occur in environmental conditions typical of the Coprinisphaera ichnofacies, mainly in soils above the groundwater table.