Naktodemasis bowni: New ichnogenus and ichnospecies for adhesive meniscate burrows (AMB), and paleoenvironmental implications, Paleogene Willwood Formation, Bighorn Basin, Wyoming

Adhesive meniscate burrows (AMB) are common in alluvial paleosols of the Paleogene Willwood Formation, Bighorn Basin,Wyoming. AMB are sinuous, variably oriented burrows composed of a nested series of distinct, ellipsoidal packets containing thin, tightlyspaced menisci subparallel to the bounding packet. Menisci are non-pelleted and texturally homogeneous with each other and the surrounding matrix. AMB were constructed most likely by burrower bugs (Hemiptera: Cydnidae), cicada nymphs (Hemiptera: Cicadae), and less likely byscarabaeid (Coleoptera: Scarabaeidae) or carabid beetles (Coleoptera: Carabidae), based on burrow morphology and comparison to similar structures produced by these organisms in modern soils. Extant burrowing insects excavate backfilled burrows in well-rooted A and upper B horizons of soils generally below field capacity depending on soil type. This study demonstrates that AMB are distinct morphologically from such previously described ichnofossil s as Beaconites, Laminites, Scoyenia, Taenidium, and Ancorichnus. Naktodemasis bowni, a new ichnogenus and ichnospecies, represents burrows composed of nested ellipsoidal packets backfilled with thin, tightly spaced, menisci subparallel to the bounding packet. The presence of N. bowni indicate periods of subaerial exposure associated with pedogenic modification under moderately towell-drained soil conditions, or during periods of better drainage in imperfectly drained soils. N. bowni, therefore, can differentiate alluvial paleoenvironments from marine and lacustrine paleoenvironments, as well as periods of subaerial exposure of sediments deposited in aquatic settings.