369 GROWTH RATE AND DURATION OF GROWTH IN THE ADULT CANINE OF SMILODON GRACILIS, AND INFERENCES ON DIET THROUGH STABLE ISOTOPE ANALYSIS Robert S. Feranec 1,2 Trophic structure and interconnectedness have important implications for diversity and stability in ecosystems. While it is generally difficult to determine trophic structure and the specific prey of predators in ancient ecosystems, analysis of stable isotope ratios in tooth enamel can be used to exclude taxa from a predator’s diet. This study analyzes δ 13 C v-pdb and δ 18 O v-pdb values in a canine of Smilodon gracilis to understand tooth growth and the preferred prey of this species. Oxygen isotope results show a 5 mm/month growth rate and a duration of growth estimated to be 16 months long. The carbon isotope results suggest consumption of animals that depended only on C 3 plants. Due to overlap in δ 13 C v-pdb values, it appears that Hemiauchenia and Platygonus may have been included in the diet of this individual of S. gracilis, while Equus and Mammuthus were probably excluded. Also, the mean δ 13 C v-pdb values of S. gracilis were more negative than the prey, which may indicate prey captured in a closed environment, or consumption of species present at Leisey 1A but not yet analyzed isotopically. This study shows that determining trophic relationships and interconnectedness within ancient ecosystems is possible. Key Words: Smilodon; tooth development; diet; stable isotopes; enamel INTRODUCTION Trophic interconnectedness has important implications for diversity and stability in ecosystems (De Angelis 1975; Williams & Martinez 2000). For ancient ecosystems, this interconnectedness generally can only be inferred based on taxonomy and comparison to modern analogs. It is uncommon to be able to determine the specific prey of a particular predator. However, variation in the stable carbon isotope ratio in tooth enamel typically reflects differences in diet, and can be used to determine if a carnivore preferred prey that predominantly ate C 3 or C 4 plants, if both C 3 and C 4 plants are available (Lee- Thorp et al. 1989a, b). Using this technique it is possible to determine what taxa, or at least exclude particular taxa, on which a predator fed. The Leisey Shell Pit 1A (LSP 1A) fauna from Hillsborough County, Florida provides a unique opportu- nity to study trophic interconnectedness in an ancient ecosystem. This fauna contains numerous herbivores that can be categorized as either C 3 or C 4 feeders (Feranec & MacFadden 2000), as well as abundant car- nivores that consumed them (Berta 1995). The most common carnivore found at the LSP 1A locality was the saber-toothed felid Smilodon gracilis (Berta 1995). The evolution of a saber-toothed morphology in the upper canines of mammalian carnivores has evolved convergently at least four times, within the marsupials, creodonts, nimravids, and felids (Simpson 1941; Emerson & Radinsky 1980). Much of the research that has been conducted on the saber-toothed morphology in Smilodon has focused on determining the function of the upper canine and its use during prey capture (Simpson 1941; Gonyea 1976; Emerson & Radinsky 1980; Akersten 1985). Another line of study concentrates on determin- ing the timing and eruption sequence for the canine in Smilodon and other saber-toothed carnivores (Rawn-Schatzinger 1983; Tejada-Flores & Shaw 1984; Bryant 1988, 1990). These studies have yielded infor- mation about behavior and social dynamics within the particular taxa analyzed. Stable isotope analyses pro- vide another means for determining the growth rate and duration of tooth growth in S. gracilis, as well as for determining diet. In this study, I investigate the growth rate and du- ration of growth in the adult canine of Smilodon graci- lis, and determine whether it shows a preference for preying upon C 3 - or C 4 -feeders in the hope of determin- ing its preferred prey by analyzing stable carbon and oxygen isotope ratios found in tooth enamel. 1 Department of Integrative Biology, Museum of Vertebrate Zoology and Museum of Paleontology, University of Califor- nia, Berkeley, CA 94720; <feranec@gmail.com> 2 Current Address: Department of Biological Sciences, Stanford University, Stanford, CA 94305 Bull. Fla. Mus. Nat. Hist. (2005) 45(4): 369-377