Feranec 369 GROWTH RATE AND DURATION OF GROWTH IN THE ADULT CANINE OF SMILODON GRACILIS, AND INFERENCES ON DIET THROUGH STABLE ISOTOPE ANALYSIS Robert S. Feranec1,2 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 δ13C v-pdb and δ18O 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 δ13C 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 δ13C 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. 1Department of Integrative Biology, Museum of Vertebrate Zoology and Museum of Paleontology, University of Califor- nia, Berkeley, CA 94720; 2Current Address: Department of Biological Sciences, Stanford University, Stanford, CA 94305 Bull. Fla. Mus. Nat. Hist. (2005) 45(4): 369-377 370 CENOZOIC VERTEBRATES: Papers to Honor S. David Webb BACKGROUND ISOTOPES IN MAMMALS Variation in the oxygen isotope ratio during the ontogeny of a particular tooth has been noted in many ancient animals (Koch et al. 1989; Cerling & Sharp, 1996; Fricke & O’Neil 1996; Feranec 2004). Higher oxygen isotope ratios (18O/16O) within the tooth enamel of a particular organism suggest the ingestion of water dur- ing a warmer period (summer), while lower isotope ra- tios suggest ingestion when the water was colder (win- ter). The variation in oxygen isotope ratios may also be due to differences in source for the meteoric waters, but source variation may also be temperature depen- dant as in the seasonal rains of the central United States arising from the Gulf of Mexico or the Pacific Ocean (Amundson et al. 1996). If the duration of tooth and enamel growth extends over many warm and cold peri- ods (seasons), one would expect cyclic variation within the oxygen isotope ratio of enamel apatite. The carbon isotope ratio of mammalian apatite (e.g., bone or tooth enamel) reflects the isotopic ratio in the food of the particular animal (DeNiro & Epstein 1978; Lee-Thorp et al. 1989a, b; Koch 1998). Much related research has concentrated on determining whether her- bivores fed on plants that used either the C 3 or C 4 pho- tosynthetic pathway, but carbon isotope studies also have been applied to determining the diets of carnivores (Lee-Thorp et al. 1989a, b; Bocherens et al. 1994). Because herbivore species at LSP 1A can be classified as having preference for either C 3 or C 4 plants (Feranec & MacFadden 2000), and tooth enamel reflects the iso- tope value of the forage (Koch 1998), it is possible to use carbon isotopes to indicate if a carnivore preferred prey that were either C 3 -feeders or C 4 -feeders. In her- bivores, isotopic values more negative than -8.0‰ are indicative of a pure C 3 diet, values more positive than - 2.0‰ indicate a pure C 4 diet, and values between -8.0‰ and -2.0‰ suggest an intermediate, or mixed, C 3 -C 4 diet (MacFadden & Cerling 1996). Due to differences in fractionation of isotopes between the food and tooth enamel (Lee Thorp et al. 1989a, b), carnivores will re- flect the same isotopic values as do prey. For instance, a Smilodon that consumes only animals having foraged on C 3 plants would display δ13C values more negative than -8.0‰. Although post-depositonal diagenesis can overprint isotopic values in bone (Schoeninger & DeNiro, 1982), tooth enamel reliably reflects isotopic values de- rived from feeding, and very rarely undergoes diage- netic alteration (Quade et al. 1992; Wang & Cerling 1994; Koch et al. 1997). LEISEY SHELL PIT 1A The Leisey Shell Pit 1A fauna has been biochronologically and paleomagnetically dated to about 1.5 million years ago (Ma; Morgan & Hulbert 1995; MacFadden 1995). The LSP 1A fauna are ideal for this study. Specimens of both carnivore and herbivore spe- cies are abundant at this locality making trophic com- parisons possible. Further, the flora remove many of the problems that can occur when interpreting plant for- age type based on isotopic values. The interpretations of isotopic values for individuals within LSP 1A are such that browsing animals will have δ13C values in the C 3 range (< -8.0‰), while grass-feeding animals will have δ13C values in the C 4 range (> -2.0‰). These interpre- tations are based on previous analysis (Feranec & MacFadden 2000), what is known about the present day flora, as well as the predicted effects of climate on the isotopic values in plants during the Pleistocene. In Florida today, nearly all present-day browse is C 3 (> 97%; Stowe & Teeri 1978), while most of the grasses and sedges are C 4 (> 63% for Poaceae, and up to 43% for Cyperaceae; Teeri & Stowe 1976; Teeri et al. 1980; Sage et al. 1999). A study of modern floral composition on a site near the LSP 1A fossil locality shows that C 3 grasses and sedges may be present, but they are generally confined to wetter areas and gener- ally are not widespread on the landscape (Huffman & Judd 1998). Pollen studies from LSP 1A show a similar pollen record to that found today (Rich & Newsome 1995). Also, vegetation models during glacial stages suggest the spread of grasslands and an increase in domi- nance of grasses and sedges using C 4 photosynthesis due to decreasing CO 2 levels (Webb 1991; Ehleringer et al. 1997; Cowling 1999). This would suggest that per- centages of C 3 grasses in Florida are unlikely to have been significantly greater during the past. Further, C 4 browse is rare, so it is unlikely that percentages of these type of plants have significantly changed. COMPARATIVE RATES AND DURATIONS OF GROWTH The crown height of the saber-tooth in Smilodon gracilis is similar to modern lions and tigers. Under- standing the rate and duration of growth in the canines of the modern species may also aid in the determination of those parameters in S. gracilis. Lions and tigers appear to utilize slightly different strategies to grow their canines. Lions (Panthera leo) appear to grow their canines with a slow growth rate, but have a long dura- tion of growth. Smuts et al. (1978) showed that the 371 upper canine in P. leo, a social cat, appears in the alveoli between 9 and 11 months of age and finishes growing between 28 and 36 months. For modern lions, growth of the canines takes place between 17 and 27 months. Smuts et al. (1978) also show crown heights for indi- viduals in Kruger National Park (KNP) to be between 37 mm and 56 mm. The fastest growth rate in the lion canines at KNP is therefore 3.3 mm/month, while the slowest growth rate is 1.3 mm/month. In contrast to lions, tigers (Panthera tigris) ap- pear to growth their canines with a quick growth rate, but have a shorter duration of growth. Mazak (1981) suggested that canines of P. tigris, with crown heights of up to 75 mm, are the longest in living felids. P. tigris canines begin to erupt between 8.5 and 9.5 months of age and finish erupting between 12 and 14 months of age (Mazak 1981). The maximal rate of growth in the canines would be between 13.6 and 30.0 mm/month if the canines began to form as the first permanent tooth (upper incisor 1) started to erupt. The minimum growth rate of the tiger canine would be 5.3 mm/month if the adult canine began to grow upon the birth of the indi- vidual. Fossil data on the growth rate and duration of growth of canines for Smilodon fatalis, a closely re- lated species from Rancho La Brea, California suggest that this particular species utilized both a quick growth rate and a long duration of growth. It appears that indi- viduals of S. fatalis grew the crown of the saber-tooth at a rate up to 7mm/month and had a duration of growth of about 18 months (Feranec 2004). METHODS SAMPLE COLLECTION AND ANALYSIS One upper canine of Smilodon gracilis (UF 87259) from the Leisey Shell Pit 1A locality in Hillsborough County, Florida was obtained from the Vertebrate Pale- ontology Collections at the Florida Museum of Natural History and was sampled for both carbon (δ13C) and oxygen (δ18O) isotope values. Mammal teeth grow and develop disto-proximally such that the distal portion of the tooth crown forms when the individual is younger, while the proximal portion of the crown forms when the individual is older. The canine was ontogenetically sampled perpendicular to the growth axis of the tooth from the enamel-root junction toward the tip of the ca- nine. Sampling involved drilling ~5 mg of pristine enamel along visible growth increments using a 0.3 mm round tip carbide drill bit and a variable speed Dremel ™ ro- tary tool (Fig. 1). The pristine enamel powder was then prepared similar to the procedures described by MacFadden and Cerling (1996) and Koch et al. (1997). The powder was first treated with 30% hydrogen per- oxide for 24 hours to remove organics, then decanted Figure 1. The upper canine of Smilodon gracilis (UF 87259) before and after isotopic sampling. Thirteen isotope samples were taken over 60 mm of the 80 mm length of canine enamel. FERANEC: Canine Growth in Smilodon gracilis 372 CENOZOIC VERTEBRATES: Papers to Honor S. David Webb and washed with distilled water, soaked in 0.1 N acetic acid for 24 hours to remove any diagenetic carbonate, decanted and washed again with distilled water, rinsed with 100% ethyl alcohol, and dried overnight. A total of 13 samples were collected and prepared from the ca- nine. After treatment, the samples were analyzed using an ISOCARB automated carbonate preparation system attached to a Micromass Optima gas source mass spec- trometer within the Department of Earth and Ocean Sciences at the University of California, Santa Cruz. The ~1 mg samples were dissolved in 100% phosphoric acid at 90ºC to create CO 2 . The results were compared using the following equation X = [(R sample /R standard )-1] * 1000. Where X is the δ13C or δ18O value, and R = 13C/ 12C or 18O/16O, and all isotope values are reported rela- tive to V-PDB (Coplen, 1994). The precision for the analysis was 0.1‰ for carbon and 0.1‰ for oxygen. HERBIVORES OF THE LEISEY SHELL PIT Stable carbon isotope data for Equus (horse), Hemiauchenia (camelid), Mammuthus (mammoth), and Platygonus (peccary) from the LSP 1A locality were gathered from the literature (MacFadden & Cerling 1996; Feranec & MacFadden 2000; Feranec 2003). There were 28 total prey specimens included in this study, 7 Equus specimens, 10 specimens of Hemiauchenia, 6 specimens of Mammuthus, and 5 specimens of Platygonus (Appendix 1). Mean differences among the herbivores and between Smilodon gracilis and the herbivores were compared by using ANOVA and LSD tests. LSD tests are similar to t-tests but take into ac- count multiple comparisons. Statistical analyses were run on Microsoft Excel 2000 and SPSS Student Version 8.0 for Windows, with significance set at p<0.05. RESULTS CARBON ISOTOPE ANALYSIS OF LEISEY SHELL PIT 1A HERBIVORES The mean d13C v-pdb value for Equus was -3.0‰ with a standard deviation of 1.3‰, and a range from -5.1‰ to -1.5‰ (Table 1, Appendix 1). The mean d13C v-pdb value for Hemiauchenia was -6.4‰ with a standard deviation of 2.2‰, and a range from -8.7‰ to -3.2‰. The mean d13C v-pdb value for Mammuthus was -2.5‰ with a standard deviation of 1.3‰, and a range from -4.6‰ to -0.6‰. Platygonus had a mean d13C v- pdb value of -7.0‰ with a standard deviation of 2.0‰, and a range from -9.2‰ to -3.9‰. Equus was signifi- cantly different in carbon isotope value from both Hemiauchenia (p<0.001) and Platygonus (p<0.001). Equus did not differ from Mammuthus. Stable carbon isotope values for Mammuthus were significantly dif- Table 1. δ13C values and predicted diets for the large herbi- vores in Leisey Shell Pit 1A. Data obtained from MacFadden and Cerling (1996), Feranec and MacFadden (2000), and Feranec (2003). Genus Mean δ13C Value Diet (Range) Equus -3.0‰ C 4 grazer (-5.1‰ to -1.5‰) Hemiauchenia -6.4‰ Intermediate (-8.7‰ to -3.2‰) Feeder Mammuthus -2.5‰ C 4 grazer (-4.6‰ to -0.6‰) Platygonus -7.0‰ Intermediate (-9.2‰ to -3.9‰) Feeder Sample Name Distance (in mm) δ13C δ18O RSF 0109A 6.2 -8.3 -0.4 RSF 0109B 10.9 -8.3 -0.6 RSF 0109C 17.3 -8.3 -0.7 RSF 0109D 21.9 -8.9 -0.6 RSF 0109E 27.7 -9.0 -0.4 RSF 0109F 30.6 -9.0 -0.1 RSF 0109G 33.0 -9.1 0.6 RSF 0109H 36.5 -8.9 0.2 RSF 0109I 40.8 -8.8 0.8 RSF 0109J 44.5 -8.9 0.7 RSF 0109K 48.5 -8.8 1.0 RSF 0109L 53.1 -8.8 1.3 RSF 0109M 57.3 -8.9 1.0 Table 2. Isotopic results of Smilodon gracilis from the Leisey Shell Pit 1A locality, Hillsborough County, Florida. Distance is given from the enamel-root contact on the anterior of the canine. All isotopic values are given relative to the V-PDB. 373 ferent from both Hemiauchenia (p<0.001) and Platygonus (p<0.001). Stable carbon isotope values did not differ between Hemiauchenia and Platygonus. SMILODON GRACILIS OXYGEN ISOTOPE ANALYSIS The oxygen isotope values within the Smilodon gracilis canine had a mean δ18O v-pdb value of 0.2‰ with a standard deviation of 0.7‰, and ranged from -0.7‰ to 1.3‰ (Table 2, Fig. 2a). The oxygen isotope pattern suggests enamel growth during different seasons when the water ingested was warmer (summer) and colder (winter). The pattern indicates that nearly one year was sampled, showing about 60 mm of enamel growth over the year, resulting in a growth rate of about 5 mm/month. The total length of enamel in the S. gracilis canine was estimated to be 80 mm implying a 16-month growth pe- riod if enamel growth rate remained constant. SMILODON GRACILIS CARBON ISOTOPE ANALYSIS The mean δ13C v-pdb value for Smilodon gracilis was -8.8‰ with a standard deviation of 0.3‰, and a range from -9.1‰ to -8.3‰ (Table 2, Fig. 2b). The carbon isotope values from S. gracilis suggest consump- tion of animals that depended primarily on a diet of C 3 plants. These values generally concentrate near -8.9‰, except for the last three samples when the individual was older, which concentrate near -8.3‰. The carbon isotope values do not show the same type of seasonal fluctuation, as did the oxygen isotope values. Stable carbon isotope values in S. gracilis were significantly different from Equus (p<0.001), Hemiauchenia (p<0.001), Mammuthus (p<0.001), and Platygonus (p<0.032). DISCUSSION The results from the δ18O analysis in Smilodon graci- lis shows that the rate of growth for the canine is about 5 mm/month, and it had a duration of growth of about 16 months. These results are similar to the growth rate and duration of growth found in S. fatalis from Rancho La Brea, which had a growth rate of about 7 mm/month and a growth period of about 18 months (Feranec 2004). Similar to S. fatalis, the canine of S. gracilis appears to have achieved its large size by having a quick growth rate and a long duration of growth. Knowing the δ13C values of this individual of Smilodon gracilis, and the values of some of the major herbivores of the LSP 1A Local Fauna (Fig. 3), it is possible to determine what taxa, or at least exclude taxa, on which S. gracilis fed. The data suggest that S. gra- cilis did not commonly feed on either Equus or Mammuthus. This result is similar to that found for S. fatalis and the general exclusion of Equus from its diet (Coltrain et al. 2004; Feranec 2004; Kohn et al. 2005). The data also suggest that S. gracilis differed from Hemiauchenia and Platygonus. However, there is some overlap in δ13C values between this individual of Smilodon and for individuals of both Hemiauchenia and Platygonus (Fig. 3), so that these genera cannot be excluded from the general diet. The mean δ13C value for the S. gracilis specimen is more negative than the mean values of the other herbivore species studied. One reason for this negative value might be due to the hunt- ing of prey, which lived in more closed habitat. The negative values observed in the saber-tooth may reflect a closed canopy effect (van der Merwe & Medina 1991). A second reason for the negative values in S. gracilis might be its having eaten individuals from species that have yet to be sampled isotopically, which themselves have more negative δ13C values. Species such as Tapirus haysii, Palaeolama mirifica, and Odocoileus Figure 2. Oxygen (A) and Carbon (B) isotope results for Smilodon gracilis (UF 87259). Results suggest that nearly one year was sampled and this individual had a growth rate of about 5 mm/month. This individual also showed a preference for feeding on animals that had a strict C 3 diet. FERANEC: Canine Growth in Smilodon gracilis 374 CENOZOIC VERTEBRATES: Papers to Honor S. David Webb virginianus are all known to occur at LSP 1A, are sus- pected to inhabit more closed canopy environments, and feed on C 3 plants (Morgan & Hulbert 1995; MacFadden & Cerling 1996; Kohn et al. 2005). To elucidate why S. gracilis has such negative δ13C values, more isotopic analyses will need to be completed. CONCLUSIONS The isotopic data presented here suggests that the growth rate for the canine in Smilodon gracilis was about 5 mm/month, while the duration of growth was about 16 months. The data also showed that S. gracilis preyed upon individuals that had a strict C 3 diet, at least during the time while the adult canine of the analyzed individual was growing. Carbon isotope data from Equus, Hemiauchenia, Mammuthus, and Platygonus suggest that Equus and Mammuthus were not commonly in- cluded in the diet while the canine was forming. Hemiauchenia and Platygonus could not be excluded from the general diet of S. gracilis, due to overlap in carbon isotope values. Because the carbon isotope val- ues of S. gracilis were more negative, in general, than many of the individual herbivores at the Leisey Shell Pit 1A locality, the data might be reflecting prey capture in a closed environment with the more negative numbers symptomatic of a canopy effect, or consumption of spe- cies that have yet to be sampled isotopically. More iso- topic analyses will need to be completed to determine what is causing the negative d13C values in S. gracilis. Finally, this study shows that determining trophic rela- tionships and interconnectedness between organisms within a particular ancient ecosystem is possible. Figure 3. Comparison of the carbon isotope results of the herbivores and Smilodon gracilis from the Leisey Shell Pit 1A locality. These data suggest that Equus and Mammuthus were generally not included in the diet of S. gracilis, while Hemiauchenia and Platygonus could not be excluded from its diet due to overlap with some individual carbon isotope values. 375 ACKNOWLEDGEMENTS I would like to thank Dave Webb, first for his enthusi- asm for this project, but also for the time he would make when questions arose during my Master’s thesis research within the museum. Despite his busy schedule, Dave always took the time to answer any question that I had. His enthusiasm for my research made me even more excited to complete it. I thank Gary Morgan for coordi- nating this volume. This study was improved thanks to discussions with A. D. Barnosky, M. A. Carrasco, K.C. Feranec, B. Kraatz, E. B. Davis, P. Higgins, S. S. B. Hopkins, G. Morgan, and C. Shaw. I thank R. A. Feranec for her skillful illustration. Funding was provided by Sigma Xi, and the University of California Museum of Paleontology. I thank the Florida Museum of Natural History, especially Dave Webb and Richard Hulbert, for permission to sample this individual. I thank P. L. Koch for running the isotope samples at the University of Cali- fornia, Santa Cruz. This is University of California Mu- seum of Paleontology contribution number 1889. REFERENCES CITED Akersten, W. A. 1985. Canine function in Smilodon (Mamma- lia; Felidae; Machairodontinae). Contributions in Sci- ence, Natural History Museum, Los Angeles County, 356:1-22. Amundson, R., O. Chadwick, C. Kendall, Y. Wang, & M. DeNiro. 1996. Isotopic evidence for shifts in atmospheric circulation patterns during the late Quaternary in mid-North America. Geology, 24(1):23-26. Berta, A. 1995. Fossil carnivores from the Leisey Shell Pits, Hillsborough County, Florida. Bulletin of the Florida Museum of Natural History, 37(14):463-500. Bocherens, H., M. Fizet, & A. Mariotti. 1994. Diet, physiology and ecology of fossil mammals as inferred from stable carbon and nitrogen isotope biogeochemistry: implica- tions for Pleistocene bears. Palaeogeography, Palaeoclimatology, Palaeoecology, 107(3-4):213-225. Bryant, H. N. 1988. Delayed eruption of the deciduous upper canine in the sabertoothed carnivore Barbourofelis lovei (Carnivora, Nimravidae). Journal of Vertebrate Paleon- tology, 8(3):295-306. Bryant, H. N. 1990. Implications of the dental eruption se- quence in Barbourofelis (Carnivora, Nimravidae) for the function of upper canines and the duration of parental care in sabertoothed carnivores. Journal of Zoology (Lon- don), 222:585-90. Cerling, T. E., & Z. D. Sharp. 1996. Stable carbon and oxygen isotope analysis of fossil tooth enamel using laser abla- tion. Palaeogeography, Palaeoclimatology, Palaeoecology, 126(1-2):173-186. Coltrain, J. B., J. M. Harris, T. E. Cerling, J. R. Ehleringer, M-D Dearing, J. Ward, & J. Allen. 2004. Rancho La Brea stable isotope biogeochemistry and its implications for the palaeoecology of late Pleistocene, coastal southern Cali- fornia. Palaeogeography, Palaeoclimatology, Palaeoecology, 205(3-4):199-219. Coplen, T. B. 1994. Reporting of stable hydrogen, carbon, and oxygen isotopic abundances. Pure and Applied Chem- istry, 66:273-276. Cowling, S. A. 1999. Simulated effects of low atmospheric CO 2 on structure and composition of North American veg- etation at the Last Glacial Maximum. Global Ecology and Biogeography, 8(2):81-93. De Angelis, D. L. 1975. Stability and connectance in food web models. Ecology, 56(1):238-243. DeNiro, M. J., & S. Epstein. 1978. Carbon isotopic evidence for different feeding patterns in two hyrax species occu- pying the same habitat. Science, 201:906-908. Ehleringer, J. R., T. E. Cerling, & B. R. Helliker. 1997. C 4 photo- synthesis, atmospheric CO 2 , and climate. Oecologia, 112(3):285-299. Emerson, S. B., & L. Radinsky. 1980. Functional analysis of sabertooth cranial morphology. Paleobiology, 6(3):295-312. Feranec, R. S. 2003. Stable isotopes, hypsodonty, and the paleodiet of Hemiauchenia (Mammalia: Camelidae), a morphological specialization creating ecological gener- alization. Paleobiology 29(2):230-242. Feranec, R. S. 2004. Isotopic evidence of saber-tooth devel- opment, growth rate, and diet from the adult canine of Smilodon fatalis from Rancho La Brea. Palaeogeography, Palaeoclimatology, Palaeoecology, 206(3-4):303-310. Feranec, R. S., & B. J. MacFadden. 2000. Evolution of the grazing niche in Pleistocene mammals from Florida: evi- dence from stable isotopes. Palaeogeography, Palaeoclimatology, Palaeoecology, 162(1-2):155-169. Fricke, H. C., & J. R. O’Neil. 1996. Inter- and intra-tooth varia- tion in the oxygen isotope composition of mammalian tooth enamel phosphate: implications for palaeoclimatological and palaeobiological research. Palaeogeography, Palaeoclimatology, Palaeoecology, 126(1-2):91-99. Gonyea, W. J. 1976. Behavioral implications of saber-toothed felid morphology. Paleobiology, 2(4):332-42. Huffman, J. M., & W. S. Judd. 1998. Vascular flora of Myakka River State Park, Sarasota and Manatee Counties, Florida. Castanea, 63:25-50. Koch, P. L. 1998. Isotopic reconstruction of past continental environments. Annual Review of Earth and Planetary Science, 26:573-613. Koch, P. L., D. C. Fisher, & D. Dettman. 1989. Oxygen isotope variation in the tusks of extinct proboscideans: a mea- sure of season of death and seasonality. Geology, 17(6):515-519. FERANEC: Canine Growth in Smilodon gracilis 376 CENOZOIC VERTEBRATES: Papers to Honor S. David Webb Koch, P. L., N. Tuross, & M. L. Fogel. 1997. The effects of sample treatment and diagenesis on the isotopic integ- rity of carbonate in biogenic hydroxylapatite. Journal of Archaeological Science, 24(5):417-429. Kohn, M. J., M. P. McKay, & J. L. Knight. 2005. Dining in the Pleistocene - Who’s on the menu? Geology, 33:649-652. Lee-Thorp, J. A., J. C. Sealy, & N. J. van der Merwe. 1989a. Stable carbon isotope ratio differences between bone collagen and bone apatite, and their relationship to diet. Journal of Archaeological Science, 16:585-99. Lee-Thorp, J. A., N. J. van der Merwe, & C. K. Brain. 1989b. Isotopic evidence for dietary differences between two extinct baboon species from Swartkrans. Journal of Hu- man Evolution, 18:183-190. MacFadden, B. J. 1995. Magnetic polarity stratigraphy and correlation of the Leisey Shell Pits, Hillsborough County, Florida. Bulletin of the Florida Museum of Natural His- tory, 37(3):107-116. MacFadden, B. J., & T. E. Cerling. 1996. Mammalian herbivore communities, ancient feeding ecology, and carbon iso- topes: a 10 million-year sequence from the Neogene of Florida. Journal of Vertebrate Paleontology, 16(1):103- 115. Mazak, V. 1981. Panthera tigris. Mammalian Species, 152:1-8. Morgan, G. S., & R. C. Hulbert Jr. 1995. Overview of the geol- ogy and vertebrate biochronology of the Leisey Shell Pit Local Fauna, Hillsborough County, Florida. Bulletin of the Florida Museum of Natural History, 37(1):1-92. Quade, J., T. E. Cerling, J. C. Barry, M. E. Morgan, D. R. Pilbeam, A. R. Chivas, J. A. Lee-Thorp, & N. J. van der Merwe. 1992. A 16-Ma record of paleodiet using carbon and oxy- gen isotopes in fossil teeth from Pakistan. Chemical Ge- ology (Isotope Geosciences Section), 94:183-92. Rawn-Schatzinger, V. 1983. Development and eruption se- quence of deciduous and permanent teeth in the saber-tooth cat Homotherium serum Cope. Journal of Vertebrate Paleontology, 3(1):49-57. Rich, F. J., & L. A. Newsom. 1995. Preliminary palynology and macroplant report for the Leisey Shell Pits, Hillsborough County, Florida. Bulletin of the Florida Museum of Natu- ral History, 37(4):117-126. Sage, R. F., D. A. Wedin, & M. Li. 1999. The biogeography of C 4 photosynthesis: patterns and controlling factors. Pp. 313-373 in R. F. Sage and R. K. Monson, eds. C 4 Plant Biology. Academic Press, New York. Schoeninger, M. J., & M. J. DeNiro. 1982. Carbon isotope ratios of apatite from fossil bone cannot be used to re- construct diets of ancient animals. Nature, 297:577-578. Simpson, G. G. 1941. The function of saber-like canines in car- nivorous mammals. American Museum Novitates 1130:1-12. Smuts, G. L., J. L. Anderson, & J. C. Austin. 1978. Age determi- nation of the African Lion. Journal of Zoology, London, 185:115-146. Stowe, L.G., & J. A. Teeri. 1978. The geographic distribution of C 4 species of the Dicotyledonae in relation to climate. American Naturalist, 112:609-623. Teeri, J.A., & L. G. Stowe. 1976. Climatic patterns and the dis- tribution of C 4 grasses in North America. Oecologia, 23:1-12. Teeri, J.A., L. G. Stowe, & D. A. Livingstone. 1980. The distri- bution of C 4 species of the Cyperaceae in North America in relation to climate. Oecologia, 47:307-310. Tejada-Flores, A. E., & C. A. Shaw. 1984. Tooth replacement and skull growth in Smilodon from Rancho La Brea. Jour- nal of Vertebrate Paleontology, 4(1):114-121. van der Merwe, N.A., & E. Medina. 1991. The canopy effect, carbon isotope ratios and foodwebs in Amazonia. Jour- nal of Archaeological Science, 18:249-259. Wang, Y., & T. E. Cerling. 1994. A model of fossil tooth and bone diagenesis: implications for paleodiet reconstruc- tion from stable isotopes. Palaeogeography, Palaeoclimatology, Palaeoecolology, 107(3-4):281-289. Webb, S. D. 1991. Historical Biogeography. Pp. 70-100 in R. L. Myers and J. J. Ewel, eds. Ecosystems of Florida. Uni- versity of Central Florida Press, Orlando. Williams, R. J., & N. D. Martinez. 2000. Simple rules yield com- plex food webs. Nature, 404:180-183. 377 Sample Number Genus UF Catalog Number Element δ13C value RSF-1 Equus 65461 Lm3 -1.9 RSF-2 Equus 65462 Lm3 -1.7 RSF-3 Equus 63880 Lm3 -3.6 RSF-4 Equus 86077 Lm3 -3.6 RSF-5 Equus 63876 Lm3 -5.1 RSF-7 Platygonus 87834 RM3 -6.6 RSF-8 Platygonus 63922 Lm3 -8.0 RSF-9 Platygonus 87830 Lm3 -9.2 RSF-10 Platygonus 81238 Rm3 -7.4 RSF-11 Platygonus 80117 Lm3 -3.9 RSF-13 Mammuthus 81707 Rm3 -2.7 RSF-14 Mammuthus 86975 Lm3 -2.4 RSF-15 Mammuthus 86137 Rm -2.0 RSF-16 Mammuthus 86974 Rm3 -2.7 RSF-17 Mammuthus 67451 M3 -4.6 RSF-19 Hemiauchenia 64219 Lm3 -8.0 RSF-20 Hemiauchenia 80053 Rm3 -8.3 RSF-21 Hemiauchenia 142321 Lm3 -5.6 RSF-22 Hemiauchenia 64315 LP4 -8.3 RSF-23 Hemiauchenia 83964 RP4 -3.6 MCF&C 96-81 Equus 80047 M3 -1.5 MCF&C 96-83 Equus None Rp2 -3.5 MCF&C 96-85 Mammuthus None M plate -0.6 RSF 0036 Hemiauchenia 132000 Rm3 -3.2 RSF 0037 Hemiauchenia 84239 LP3 -4.0 RSF 0038 Hemiauchenia 85085 RM -8.7 RSF 0039 Hemiauchenia 80737 RP4 -8.2 RSF 0040 Hemiauchenia 83965 RM3 -6.2 Appendix 1. Sample number, Genus, UF Catalog Number, Element, and δ13C value for the individual herbivores from the Leisey Shell Pit 1A locality included in this study. Abbreviations: L, Left; R, Right; M, upper molar; m, lower molar; P, upper premolar; p, lower premolar; # refers to tooth position. RSF-## refers to data from Feranec and MacFadden (2000), MCF&C ##-## refers to data from MacFadden and Cerling (1996), and RSF 00## refers to data from Feranec (2003). FERANEC: Canine Growth in Smilodon gracilis 378 CENOZOIC VERTEBRATES: Papers to Honor S. David Webb