The trace fossil <i>Asthenopodichnium</i> from the Upper Cretaceous of northwestern New Mexico

Abstract

Asthenopodichnium is a trace fossil consisting of aligned and overlapping, lozenge-or pouch-shaped borings or cavities in wood, bone or coal substrates known from a handful of Cretaceous and Cenozoic records and attributed to either mayfly nymph boring or fungal rot. We add to the sparse record of this trace fossil two new occurrences, in the Campanian Menefee and Kirtland formations in northwestern New Mexico. The Menefee record is from the lower Campanian Allison Member in the Piedra Lumbre Arroyo drainage in Sandoval County. The Kirtland specimens are from the upper Campanian Hunter Wash Member in the Chaco River drainage. These traces are dense concentrations of aligned and variously overlapping, lozenge-shaped chambers in the wood xylem that we assign to Asthenopodichnium lignorum Genise et al. The Asthenopodichnium traces suggest freshwater, humid and subaerial conditions at the time of their formation. The presence of Asthenopodichnium in the Kirtland and Menefee formations is thus an important paleoecological indicator of freshwater deposition in systems that were deposited near the shoreline of the Cretaceous Western Interior seaway. They are also the first published evidence of wood-rotting fungi (the most likely tracemaker from the Kirtland and Menefee formations). Further work on trace fossils in wood in the Upper Cretaceous strata of northwestern New Mexico will no doubt reveal greater diversity and provide additional paleoecological information.