WHAT A SPREAD! ISOTOPIC VARIABILITY SUGGESTS DEPOSITION OF NON-LOCAL LATE HOLOCENE SKELETAL MATERIAL IN A TROPICAL CAVE.

We set out to investigate the foraging ecology of extinct rodents preserved at Trou Jean Paul (TJP), a small, multichambered cave with a vertical entrance chamber eroded into Eocene limestone in southwestern Haiti. TJP sits ca. 1800 m above sea level and is currently surrounded by endemic pine forest. It contains abundant, well-preserved skeletal material from recently extinct vertebrates. Collagen stable carbon and nitrogen isotope data for the two most abundant endemic rodents, Brotomys sp. and Isolobodon portoricensis, are quite variable: d¹³C ranges from -21.1 to -17.2‰ and -20.3 to -16.2‰ for the two taxa, while d ¹⁵N ranges from 1.1 to 6.3‰ and 4.1 to 8.9‰ respectively. These values are more variable than expected for herbivorous rodents inhabiting high elevation pine forest, suggesting that there was either a temporal shift in local vegetation or foraging behavior for the two species, or that some rodents were not local. We used radiocarbon dating and strontium isotopes (⁸⁷Sr/⁸⁶Sr) to investigate these possibilities. We can rule out temporal changes; dates for most of the sampled rodents are 778-1249 calendar years before present. Sr isotopes, which reflect the geology where an animal forages, range from 0.70776 to 0.70899, which is higher than expected for the local Eocene limestone. We suggest that some of the sampled individuals were transported by owls or other avian predators. This scenario is supported by the presence of modern owl roosts in TJP’s entrance chamber. Additionally, most skeletal remains in this part of TJP are disarticulated small-bodied rodents and birds.

Most ancient skeletal material preserved in the tropics hails from caves and sinkholes. We tend to assume that preserved animals were local, but this may not be the case. Small vertebrates, especially, can be transported relatively long distances by predators. Uncertainty in the provenance of remains can make it challenging to interpret isotopic, biogeographical, or phylogenetic data, and we urge researchers to consider taphonomic and depositional conditions when analyzing cave-deposited material.