Diet and water source of Pleistocene Lamini camelids based on stable isotopes of tooth enamel: Implications for North American vegetation and paleoclimate

Abstract

Arid adapted taxa have evolved to live in some of the harshest environments on Earth, yet the adaptations that allowed them to transition from mesic to arid landscapes is poorly understood. Members of Camelidae (camels, vicunas, guanacos) provide a unique opportunity to study past climates as their ancestors are ubiquitous in the fossil record and all extant taxa live in arid environments. This dissertation examines Pleistocene Lamini camelids (<em>Camelops</em>, <em>Hemiauchenia</em>, <em>Palaeolama</em>); to better understand the paleoecology of the ancestors of modern South American camelids (<em>Vicugna</em>, <em>Lama</em>). To reconstruct the diet and ecology of these camelids, stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope values were used as a proxy for the vegetation and water consumed by herbivores. An aridity index was further developed and identified camelids as sensitive to changes in aridity. Examination of community sites in Florida suggests that warmer and drier sites had more heterogeneous environments during the Pleistocene, and likely provided the vegetation needed to support closely related taxa. In response to warmer temperatures and more heterogeneous environments, <em>Hemiauchenia</em>, <em>Platygonus</em>, and <em>Mylohyus </em>modified their dietary niches, but δ¹³C values suggest that <em>Equus</em>, <em>Mammut</em>, <em>Palaeolama</em>, and <em>Tapirus</em> were dietary specialist. The integration of δ¹³C and δ¹⁸O values indicates that <em>Palaeolama</em> was a specialized forest browser that did not modify its dietary niche in response to environmental changes or changes in the faunal composition of past ecosystems. This interpretation is further supported by its frequent co-occurrence with forest browsing <em>Tapirus</em> and <em>Odocoileus</em>. <em>Hemiauchenia</em> was a true dietary generalist that could modify its diet in response to environmental changes and/or the presence of either <em>Palaeolama </em>or <em>Camelops</em>. Potential consumption of C₄ saltbush suggests <em>Camelops</em> was an opportunistic browser that may have taken advantage of its large body size and varied browsing diet to co-occur with <em>Palaeolama</em> or <em>Hemiauchenia</em>. Co-occurrence with a broader range of taxa further suggests that <em>Hemiauchenia</em> and <em>Camelops</em> lived in a range of habitats. This work further clarifies the isotopic ecology of three Pleistocene Lamini camelids, and suggests the opportunistic behavior of <em>Hemiauchenia</em> and its descendants potentially allowed for the adaptation to harsh, arid environments.