The foraging pits of the nine-banded armadillo, Dasypus novemcinctus (Mammalia: Xenarthra: Dasypodidae), and implications for interpreting conical trace fossils

The nine-banded armadillo (Dasypus novemcinctus) is a well known burrower, but individuals spend the majority of their time above ground foraging for soil organisms by repeatedly digging pits through the soil surface. Little ichnological attention has been given to these foraging pits even though their great prevalence within the geographic range of extant armadillos implies that they might have a trace fossil record in paleosols extending back to at least the Paleocene. This research describes the foraging pits constructed by D. novemcinctus with implications for recognition and interpretation of similar conical trace fossils. Field observations yielded an association between one large-diameter (41 cm wide) dwelling burrow, three relatively short, straight shelter burrows (up to 19 cm wide and 38 cm long), and abundant variously sized foraging pits (up to 18 cm wide and 14.5 cm deep). Plaster casts of foraging pits showed that most were asymmetrical, vertically oriented, downward-tapering elliptical cones (width>depth), with smooth to coarsely dimpled walls and common elongate, parallel grooves, isolated curved grooves, and distinct paired grooves, resulting from scratching with the elongated middle two digits of the forelimb. Digital models of plaster casts are used to quantify several aspects, including a new property, conicality. Relative compactness and volume exploited indicate that surface pits are more efficient for soil foraging than subterranean burrows. Recognition of fossil armadillo foraging pits would enable paleoenvironmental and paleoclimatic interpretations analogous to the habitats and ranges of extant armadillos. Conical trace fossils in the Upper Jurassic Morrison Formation are potential examples of ancient vertebrate foraging pits, although they are not attributable to armadillos because of their age. Brian F. Platt. Department of Geology and Geological Engineering, University of Mississippi, 120A Carrier Hall, University, Mississippi 38677, USA [email protected]