The biogeography of “breas”: Contextualizing the taphonomy, ecology, and diversity of Trinidad’s asphaltic fossil record

Abstract

While the lagerstätte Rancho La Brea in California, USA has yielded millions of specimens, fossiliferous asphaltic deposits (“tar pits” or “breas”) are globally rare, with <15 localities. In the neotropics, such deposits represent opportunities for preservation in otherwise challenging tropical climates. The Caribbean island of Trinidad contains the largest natural asphalt deposit in the world and has a fragmentary record of brief excavations in the early-mid 1900s. We integrated information from collections databases with archival research and field surveys to verify localities, reconstruct taphonomic scenarios, and compile the first comprehensive Pleistocene faunal record for terrestrial Trinidad. To guide interpretations of this poorly sampled region, we conducted a quantitative synthesis of megafaunal mammal abundance data from all known “tar pits” of the western hemisphere, including metrics for sampling coverage and ecological diversity. Based on these metrics, condition of skeletal material, and descriptions of geology, we suggest that the megafaunal remains from Trinidadian localities represent secondary asphaltic preservation, in which hydrocarbons infiltrated in-situ Pleistocene bone beds, thus guiding future excavation approaches. The orders Cingulata, Pilosa, Proboscidea and Rodentia are represented, with genera that are ecologically consistent with the former savanna connection of Trinidad and Venezuela. Using this information, we infer the Quaternary biogeographic and paleoenvironmental history of Trinidad and demonstrate sized-biased extinctions. Finally, we identify interdisciplinary opportunities to study the actualistic taphonomy and ecology of active asphalt seeps today. Our study contributes both to our understanding of the paleoecology of the Caribbean and northern South America, as well as “tar pits” globally.