DIETARY VARIABILITY IN CAMELOPS, HEMIAUCHENIA, AND PALAEOLAMA OF THE AMERICAS DURING THE PLIO-PLEISTOCENE

Stable carbon (δ¹³C) isotope values from tooth enamel are used to reconstruct diet and dietary variability in mammals. We aim to clarify the dietary variability for Camelops (n=80), Hemiauchenia (n=122), and Palaeolama (n=44) using new and published data from North and South America. Palaeolama specimens have the narrowest range in δ¹³C values from -15.7‰ to -7.2‰ and the lowest mean value of -12.0‰. Camelops has an intermediate range from -12.0‰ to 1.0‰ and the greatest mean δ¹³C value of -6.6‰. Hemiauchenia has the widest range in δ¹³C values from -14.7‰ to 2.1‰ and an intermediate mean δ¹³C value of -7.8‰. Sites with ≥5 specimens belonging to the same genus were used to investigate dietary variability at a given site. Nine of 24 sites have ≥5 Hemiauchenia specimens and δ¹³C ranges were between 1.5 and 15.4‰. Six of 20 sites have ≥5 Camelops specimens and δ¹³C ranges were between 3.3 and 13.0‰. Four of 8 sites have ≥5 Palaeolama specimens and δ¹³C ranges were low, between 1.5 and 4.3‰. Hemiauchenia has the greatest overall range and the greatest variability in δ¹³C values at a given site. These data suggest Hemiauchenia could be a dietary specialist or a generalist and had the most variable diet; this is consistent with morphological and dental microwear data. Camelops also has highly variable δ¹³C values at a given site, but previous work suggests that Camelops may have been an obligate browser, feeding on C₃ and C₄ plants, including C₄ saltbush. Palaeolama specimens have the lowest overall range and lowest intrasite range in δ¹³C values, indicating these animals consumed a specialized diet of C₃ browse. While Hemiauchenia had the flexibility to modify its consumption of browse and grass, Camelops and Palaeolama had more specialized browse diets. High dietary variability in Hemiauchenia may have allowed them to range throughout much of the Americas and contributed to the subsequent success of their descendants, modern vicunas and guanacos.