Teeth weathering under tropical conditions: preliminary experimental results from Brazil

NAHUEL RUIZ, GABRIEL; DE ARAÚJO JÚNIOR, HERMÍNIO; TOMASSINI, RODRIGO

Rio de Janeiro

Encuentro; I Semana Acadêmica do Programa de Pós-graduação em Geociências; 2025

Universidade do Estado do Rio de Janeiro. Faculdade de Geologia

Weathering is a key taphonomic process widely applied in paleontological, archaeological, and forensic contexts due to its value in assessing the integrity and depositional context of skeletal remains. Numerous monitored experiments in diverse natural settings worldwide have shown that continental vertebrate remains are differentially affected by weathering depending on the climatic and environmental characteristics of the area. Intrinsic properties, such as size, shape, microstructure, surface area, and density also vary among taxa, skeletal elements, and ontogenetic stages, influencing their susceptibility to alteration. While bone weathering has been extensively studied, teeth have received comparatively Little attention. This study presents preliminary results from a monitored experiment conducted between June and August at the Parque Paleontológico de São José, Itaboraí, Rio de Janeiro State, Brazil. A total of 22 fully defleshed skulls, 3 mandibles, and 10 hemimandibles were placed directly on the ground, with teeth positioned occlusal surface up for maximum sunlight exposure. The remains belonged to Hydrochoerus hydrochaeris, Canis lupus familiaris, Cerdocyon thous, Nasua nasua, and Didelphis aurita. Monitoring took place every 15 days, including photographic documentation and retrieval of environmental data (temperature, humidity, rainfall, solar radiation). After 15 days, most specimens started to exhibit bleaching of the exposed bone surfaces. Insect activity was observed, although no direct traces were recorded. Bones did not show fissuring or cracking at this stage; however, the teeth, particularly those of H. hydrochaeris, displayed rapid alteration. Cracks and fissures appeared on the occlusal surface, most frequently in the third upper molar, oriented parallel to the tooth row and primarily affecting cementum and dentine; in some cases, fissures extended into the enamel. Additionally, cracks were observed along the cement–enamel junction. The first and second upper molars showed less extensive, outward radially oriented fissures. By day 30, cracks were also evident in the incisors, and one premolar in a single specimen exhibited fragmentation, exposing underlying dentine. Comparable degrees of alteration were not observed in Canis lupus familiaris, Cerdocyon thous, or Didelphis aurita. This difference is likely linked to anatomical and histological variation: H. hydrochaeris cheek teeth are not completely covered by enamel, leaving the dentine and cementum in the occlusal area directly exposed to environmental agents. In contrast, the teeth of the other taxa are fully encased in enamel, providing a more protective barrier against weathering. The exposed softer tissues in H. hydrochaeris are more prone to moisture fluctuations, thermal stress, and microstructural expansion–contraction cycles, accelerating crack formation and propagation. These preliminary results indicate that, for certain taxa, weathering-induced modifications can develop rapidly under tropical conditions, even within a short exposure period. The experiment will continue to generate longer-term data, including an analysis of the relationship between environmental parameters and alteration rates. As this trial began during the austral winter, a comparable summer experiment is planned to assess potential seasonal differences in alteration rates, as observed in previous studies from Argentina.