Authors:Yann et alAbstract:Wild members of Camelidae live in some of the most arid environments, including North Africa, Arabia, the Gobi Desert of China and Mongolia and high elevation environments in the Andes Mountains. A better understanding of the paleoecology of the three most abundant Pleistocene camelids (Camelops, Hemiauchenia, and Palaeolama) may clarify modern adaptations to arid environments. Mammalian tooth enamel δ13C values were used to compare diets of co-occurring species in California, Texas, and Florida and δ18O values were used to investigate climate. Carbon isotope analysis suggests Camelops was likely an opportunistic browser that consumed both C3 and C4 browse/CAM plants, potentially consuming C4 browse (e.g., saltbush). Hemiauchenia had an opportunistic and highly generalized diet, while Palaeolama was a specialized forest browser. Stable oxygen isotopes and aridity index values suggest that Ingleside was warmer than McKittrick Brea, but there are no significant differences in aridity between the two sites. Co-occurrence data from the Paleobiology Database suggest that Palaeolama was restricted to forested environments as it occurred with two browsers, Tapirus and Odocoileus, at 90.5% of all sites. Camelops and Hemiauchenia both co-occurred with a broader range of taxa, further suggesting these camelids lived in diverse habitats. The generalized diet of Hemiauchenia, the likely ancestor of modern South American camelids, allowed for the adaptations of extant Lama and Vicugna to survive in the arid environments of the Andes Mountains. Collectively, these data clarify the dietary ecology of extinct camelids and provide insight into the potential importance of generalist diets for increased resilience to changing environments and/or climates.