WACO MAMMOTH NATIONAL MONUMENT (WACO MAMMOTH SITE) WAS NOT BURIED RAPIDLY

Bioerosion traces (biogenic structures that cut or destroy hard osseous tissue) on fossil assemblages can provide evidence for post-mortem exposure, environmental conditions, and scavenging behavior that may not be otherwise apparent through other lines of research. The Waco Mammoth National Monument (WMNM) likely represents the only recovered Columbian mammoth (Mammuthus columbi) nursery herd to date, which presumably perished in a catastrophic event. The assemblage was ultimately buried within an ancient river channel, as well as upon the adjacent pointbar. Furthermore, the skeletal remains exhibit a diversity of bioerosion trace fossils - traces on bone from WMNM include branching furrows (Corrosichnia type), paired grooves (Machichnus regularis and M. bohemicus), arcuate grooves that penetrate the cortical material (Brutalichnus brutalis), roughly triangular punctures with jagged margins (Nihilichnus nihilicus), and hemispherical borings (Cubiculum isp.). The branching furrows are interpreted as root-dissolution features, whereas the remaining suite of traces reveal scavenging of the mammoth corpses by rodents, carnivores, and hide beetles. Of the 21 mammoths examined in this study, 17 contain traces attributed to carnivores, demonstrating a period of subaerial exposure prior to burial, which is corroborated by sediment infill and diagenetic staining that crosscuts bone-weathering features. Eight of the specimens were gnawed on by rodents after partial skeletonization, and all but 3 of the mammoths contain borings that are consistent with those generated by modern hide (dermestid) beetles in ongoing laboratory experiments and previous reports. Since consumption of vertebrate remains by hide beetles occurs during dry-decay, and dermestid larvae avoid moisture, it can therefore be inferred that the beetles scavenged upon the mammoth corpses during a period of intense aridity while the river channel was dry. All of these ichnological constraints are contradictory to the longstanding interpretation of WMNM as being the result of a catastrophic flood with mass wasting and rapid burial.