A PROBABLE EARLY CRETACEOUS PARACOPID DUNG BEETLE NEST, UPPER YELLOW CAT MEMBER, CEDAR MOUNTAIN FORMATION, EAST-CENTRAL UTAH

In the upper Yellow Cat Member of the Cedar Mountain Formation in east-central Utah, a cluster of sediment-filled tubes is interpreted as the oldest paracopid beetle burrow system yet documented. The recognition of ichnofossils attributed to paracopid beetle coprophagy indicates that a complex food web was present in the Early Cretaceous.

The burrow system is developed in overbank deposits consisting of tan, sandy siltstone, and is overlain by sheetflood-generated intraformational conglomerates and massive sandstones. A ~70 cm thick microbial lacustrine carbonate caps the sheetflood bed. The burrow system consists of a wide ~30 cm funnel-shaped top that at its base are several vertical to subvertical tubes. A series of “chambers”, up to 5 cm in diameter, are spaced along each tube starting approximately 30 cm from the tube top. Above the funnel-shaped opening is a concentrated zone of macerated, organic-rich sediment, interpreted as a herbivorous coprolite. Filling the funnel-shaped opening is a more porous, organic-rich fine-grained sandstone passing downward into tightly packed fine-grained sandstone with a corresponding reduction in organics and the presence of a series of 5 cm diameter chambers.

The overall geometry and internal fill is consistent with features documented from modern paracopid beetle nidification. Chambers are interpreted as brood chambers that once possibly contained brood balls composed of fecal material transported downward from the overlying coprolite. This nest represents the earliest recognized example of paracopid behavior pushing back the age for this behavior from Late to Early Cretaceous, ~ 50 Ma and by extrapolation, phytophagous behavior may have evolved well before the Early Cretaceous.