Bifungites, trace fossils from Devonian-Mississippian rocks of Pennsylvania and Montana, U.S.A

Abstract

The trace fossil Bifungites Desio 1940, first recognized in Late Devonian rocks of Libya and later in Algeria, is common in Late Devonian rocks of Montana, Pennsylvania, Ohio, and Michigan, and Early Mississippian rocks of Pennsylvania. Its manifestations are given for seven stratigraphic units from forty localities in Pennsylvania, Montana, and Michigan. Bifungites commonly occur on bedding planes and consist of a horizontal shaft with doubly terminating arrow- or dumb-bell-shaped projections. Less apparent are paired vertical cylindrical sediment-filled tubes connected at their base to the bi-arrow or dumb-bell shaft. The combination represents the mud or silt casting of an inverted pi-shaped, μ, infaunal tubular burrow (domichnia). Siltstone slabs have been transversely sectioned to reveal this π-shaped, double-arrow burrow pattern with undisturbed stratification between the vertical tubes. Three new ichnospecies are proposed based on markedly different size and shape of the fossil traces in three stratigraphic zones. A Late Devonian Girard Shale type is the smallest with wide, short arrows on a narrow shaft whose median overall length is 12.5 mm. The latest Devonian Sappington type has well-formed, shortly barbed arrow terminations and median length of 28 mm. An Early Mississippian Meadville type is the largest with median length of 36 mm and prominently barbed broad arrows. The Bifungites organism is unrecognized but it was probably a sedentary, soft-bodied, infaunal suspension-feeding animal inhabiting shallow nearshore marine and brackish water environments. The identified biota directly or indirectly associated with Bifungites is extremely limited to a few brachiopods, clams, and other trace fossils.