Extreme modification of teeth and bones by porcupines (Hystrix cf. H. kiangsenensis and Atherurus macrourus) Làng Tráng Cave complex, northern Vietnam

Abstract

Identifying the causative agents of modified bone surfaces can be challenging, particularly in terrestrial systems where numerous biotic and abiotic factors can produce grooves, divots, and striae. This contribution focusses on fossil vertebrates in the Làng Tráng cave system in Vietnam, which preserves a diverse assemblage of middle Pleistocene mammals, and discusses criteria that can identify the agents responsible for the accumulation and degradation of the fossil accumulation. The Làng Tráng assemblage includes some postcranial elements and rare mandibles and skulls, but is dominated by isolated teeth and bones, particularly those of mid-sized (7-250 kg body weight) mammals. Rare long bone shafts exhibit grooves with U-shaped profiles attributable to the ichnotaxon Machichnus bohemicus. In contrast, flat-bottomed grooves attributable to M. multilineatus are exceptionally abundant. The size and shape of these traces are consistent with gnawing by moderate-sized to porcupines such as Atherurus macrourus and Hystrix kiangsenensis, both of which are represented in the Làng Tráng fauna. Porcupines are common contributors to cave faunas in Southeast Asia. The roots of most teeth exhibit moderate to severe biogenic modification, which resulted in common planar facets in some cases and reduction of the root bone to pyramidal wedges in others. The Làng Tráng cave system is unusual in that porcupines did not just contribute to the fauna; they were the dominant taphonomic factor in the accumulation and subsequent biogenic alteration/degradation of bone in these caves. Faceted and wedged roots are herein proposed as diagnostic attributes of porcupine-generated vertebrate bone accumulations.