METHODS

All fossils collected have been accessioned into the Museo de Historia Natural of the Universidad Nacional Mayor de San Marcos (MUSM) in Lima, Perú. Representative samples from all taxa are being stored in a freezer at the MUSM to preserve organics for future molecular studies. Identification of the fossil vertebrates was accomplished by comparing them to specimens in the mammal departments at the Museo de Historia Natural-UNMSM and the American Museum of Natural History as well as comparative collections in the vertebrate paleontology collections of these two institutions.

Sediment samples from Jatun Uchco and Cueva Roselló and "coprolites" (ancient feces) from Trigo Jirka were submitted for palynological analysis using the palynology collection of the Laboratorio de Palinología y Paleobotánica de la Universidad Peruana Cayetano Heredia under the direction of LH. Angiosperms were identified from pollen, and spores were used to identify ferns and club mosses (i.e., Lycopodium).

Beta Analytical (Miami) performed the radiocarbon analyses. Bone samples were washed in de-ionized water, and the outermost layers were removed by scraping. The remaining bone materials were then crushed and washed repeatedly in HCl until the mineral apatite was eliminated. Throughout this acid treatment, the remaining collagen was inspected for rootlets, which were removed if detected. The quality of the bone preservation and quantity of collagen obtained permitted an alkali pretreatment in which the collagen was washed in NaOH to ensure that all organic acids were removed. Accelerator mass spectrometry (AMS) was performed at one of the six International Consortium of Accelerator Laboratories (ICAL) on graphite (100% C) that had been reduced from the collagen samples.

In addition to ¹⁴C content, stable carbon isotope ratios (¹³C/¹²C) were obtained to verify the purity of the collagen and to apply the standard correction to Measured Radiocarbon Age to obtain the Conventional Radiocarbon Age. Dates are reported as radiocarbon years before present (RCYBP, where "present" = 1950 A.D.). Errors (±) represent one standard deviation statistics (68% probability) and were based on combined measurements of the sample, background, and modern reference standards. The measured ¹³C/¹²C ratios were calculated relative to the PDB-1 international, standard and the ages were normalized to –25 per mil to yield the Conventional Radiocarbon Age (Stuiver and Polach 1977).

DNA samples from some bones have been isolated in the Australian Center for Ancient DNA, the University of Adelaide, Australia, and the McMaster Ancient DNA Centre, Hamilton, Ontario, Canada. A report regarding the horse (†Onohippidium = Hippidion) of Cueva Roselló is forthcoming (Orlando et al. in press) and that regarding the sloth, †Diabolotherium, will be available in a few more months. We are optimistic that other phylogenetic studies will be ultimately accomplished on a number of taxa, particularly those from our highest cave (Cueva Roselló, at 3,875 m), whose fossils appear to be exceedingly well preserved in terms of their organic content.