The deposits in Cumberland Bone Cave (Allegany County, Maryland) preserved one of the most taxonomically diverse pre-radiocarbon Pleistocene faunas in the northeastern United States. The site has long been recognized as an important record of Pleistocene life in the region, but numerical age control for the fauna was never developed, and hypotheses for its age have been based upon biochronological assessments of the mammalian fauna. We used fossil teeth and preserved sediment housed in museum collections to obtain the first numerical age assessment of the fauna from Cumberland Bone Cave. Coupled U-series Electron Spin Resonance (US-ESR) was used to date fossil molars of the extinct peccary, Platygonus sp. The age estimates of two teeth gave ages of 722 ± 64 and 790 ± 53 ka. Our results are supported by previously unpublished paleomagnetic data generated by the late John Guilday, and by plotting length-width of the first molar (m1) of Ondatra (muskrats) from Cumberland Bone Cave on the chronocline of Ondatra molar evolution in North America. Our age assessments are surprisingly close to the age estimate previously proposed by Charles Repenning, who based his age on a somewhat complicated model of speciation and morphotype evolution among arvicoline rodents.

The Fairmead Landfill locality contains a diverse middle Irvingtonian, (0.78–0.55 Ma), vertebrate fauna that includes three sloths, Megalonyx wheatleyi, Nothrotheriops shastensis and Paramylodon harlani. The co-occurrence of these three genera in a single fauna is relatively rare in both the Irvingtonian and Rancholabrean and this is only the fourth documented Irvingtonian fauna to contain all three sloth genera. The presence of the three different sloths, each of which had different ecological requirements, indicates the presence of a variety of different habitats at this time and a heterogeneous landscape. Preliminary analysis of pollen from the site supports the interpretation of the existence of a mosaic of plant communities, but a landscape dominated by a mesic grassland. This interpretation is also supported by the total faunal diversity that includes taxa associated with woodlands as well as open habitat and taphonomic differences in the preservation and relative abundance of the different sloths. Evolutionarily the Fairmead Landfill sloths show a suite of morphological, size and proportional characters that indicate they represent transitional populations between older and younger members of their respective lineages.

The first appearance of mammoth (Mammuthus) is currently used to define the beginning of the Irvingtonian North American Land Mammal Age at about 1.4 Ma. Thereafter, mammoth fossils are common and widespread in North America until the end of the Pleistocene. In contrast to this generally accepted biochronology, recent reports have asserted that mammoth occurs in late Pliocene (ca. 2.5 Ma) alluvium from the Santa Fe River of northern Florida. The supposedly contemporaneous late Pliocene fossil assemblage from the Santa Fe River that produced the mammoth specimens actually consists of a mixture of diagnostic Blancan (late Pliocene) and late Rancholabrean (latest Pleistocene) species. Fossil bones and teeth of the two mammalian faunas mixed together along the Santa Fe River have significantly different rare earth element (REE) signatures. The REE signatures of mammoth are indistinguishable from those of Rancholabrean mammals, yet they are different from those of diagnostic Blancan vertebrates from these same temporally mixed faunas of the Santa Fe River. Thus, no evidence for late Pliocene mammoth exists in Florida, and mammoth fossils remain reliable biochronological indicators for Irvingtonian and Rancholabrean terrestrial sequences throughout mid- and lower-latitude North America.