The trace fossil Bifungites and its tracemaker: a rare find!

The makers of fossil burrows are rarely found preserved within them; thus, the producers even of common trace fossils are often conjectural. This is particularly the case for trace fossils like Bifungites that have no known modern analogues. From the Devonian Pimenteira Formation of Brazil, we recovered several specimens of this common Palaeozoic ichnofossil that include a polychaete, Annulitubus sp., and enough morphological evidence to support deductions concerning its behaviour. The animals lived in a shallow-marine setting of probably normal marine salinity conditions. The basic burrow consists of a straight horizontal segment (bar) with enlarged chambers at each end from which a straight vertical shaft rises, presumably to the sediment-water interface: topologically, a U. Although U-shaped burrows are abundant in the geologic record, Bifungites is the first to include a probable maker in situ, and one of very few fossil burrows to include a maker at all. The discovery of Annulitubus sp. within Bifungites confirms speculation that the maker was a "worm," possibly burrowing for protection against storm or even predation. As additional fossil burrows are associated with tracemakers, increasingly accurate palaeoecological reconstructions can be erected.