Abstract

Trace fossils of beetles and bees are preserved in the petrocalcic horizon of a Paleosol of early late Oligocene age within the upper Scenic Member of the Brule Formation in the Pinnacles area, Badlands National Park, South Dakota. The Paleosol has a greenish-gray A horizon over a reddish-brown B horizon, and it has been identified as a Petrocalcic Paleustalf. It formed under streamside, gallery woodland. This and an extensive savanna of interfluves grew in a warm temperate and subhumid climate. Near-spherical internal molds of chambers which terminated short subhorizontal branches from deep vertical burrows have been interpreted as pupal cells of beetles, most like those of dung beetles (Coleoptera, Scarabaeidae, subfamilies Geotrupinae and Scarabaeinae). Tear-shaped internal molds of subhorizontal cells clustered along deep vertical shafts are interpreted as larval cells of bees, most like those of sweat bees (Hymenoptera, Halictidae, Halictinae). These trace fossils (Celliforma ficoides ichnosp. nov.) are uncertain indicators of the degree of social behavior, which was certainly much less than that seen in modern paper wasps and honey bees. The presence of both these kinds of trace fossils supports previous hypotheses indicating the importance of dry, warm grasslands and grassy woodlands for the adaptive radiation of both dung beetles and bees during Tertiary time. The following new taxa are proposed: Pallichnus dakotensis ichnogen. et ichnosp. nov. and Celliforma ficoides ichnosp. nov.--Modified journal abstract.

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