Paleobiology, 29(2), 2003, pp. 230–242

Stable isotopes, hypsodonty, and the paleodiet of Hemiauchenia (Mammalia: ): a morphological specialization creating ecological generalization

Robert S. Feranec

Abstract.—Morphological adaptations may indicate increased specialization (narrowing of ecolog- ical niche) or expansion of the suite of lifestyles available to an organism (increasing niche breadth). Hypsodonty in generally has been interpreted as a specialization into a grazing niche from a browsing niche. Here I examine the feeding strategy of the extinct hypsodont camel Hem- iauchenia through an analysis of stable carbon isotope values from its tooth enamel, which was used to clarify its feeding strategy and to resolve conflicting interpretations of dental versus muzzle attributes. The paleodiet of Hemiauchenia is then used to test whether hypsodonty correlates to graz- ing within fossil . This study focuses on fossils from Florida, which is geographically ideal because unlike other regions of the country almost all extant plants on which browse use the C3 photosynthetic pathway. In contrast, most of the grasses and sedges utilized by grazers use the C4 photosynthetic pathway. If Hemiauchenia was an obligate grazer, the stable carbon isotope values of tooth enamel should reflect primarily a diet of C4 grass and sedge (ϾϪ1.3‰). If Hem- iauchenia was mainly a browser, the isotopic value should be considerably more negative reflecting 13 ingestion primarily of C3 browse (ϽϪ7.9‰). The mean ␦ C values for Hemiauchenia during each time interval average more negative than Ϫ8.0‰, indicating a dominantly C3 browse diet, and there is no evidence for abandonment of the browsing niche from the Hemphillian through the Ran- cholabrean North American Land Ages. However, an increase in the range of isotopic values indicates a diet with a higher proportion of C4 grasses and sedges through time. This study therefore suggests that Hemiauchenia was a hypsodont intermediate feeder with preference for browse during the past 5 million years. Hypsodonty is not strictly associated with obligate grazing; instead it may, in this case, represent an adaptation to widen niche breadth that allowed grazing as well as browsing.

Robert S. Feranec. Department of Integrative Biology and Museum of Paleontology, University of Califor- nia, Berkeley, California 94720. E-mail: [email protected]

Accepted: 31 October 2002

Introduction niche breadth by simply adding the ability to Determining the diet of ancient animals has graze. At issue is whether extinct hypsodont important implications for interpreting paleo- animals were obligate grazers, or whether community structure. For example, determin- they continued to utilize browse plants in sig- ing whether extinct herbivores are browsers, nificant quantities and added a grazing com- intermediate feeders, or grazers is required to ponent to their feeding strategy. understand details of resource partitioning, Because fossils are rarely preserved with which ultimately influences diversity in eco- any direct physical evidence of diet, indirect systems by affecting competition and allow- proxies are commonly used to assess feeding ing for the co-occurrence of species (Hutch- strategies. Dietary proxies include morpho- inson 1958). The interpretation of feeding logical characteristics of the skull, such as strategy for ungulates is that there was a pro- hypsodonty of teeth and shape of the muzzle. gression through a pathway from browsing to Such data, however, can lead to conflicting in- intermediate feeding to grazing, with the an- terpretations of diet (Webb 1974; Dompierre cestral state in diet being browsing and the and Churcher 1996). A prime example of this derived state being grazing (Perez-Barberia et conflict involves the feeding ecology of Hem- al. 2001). What has been unclear, however, is iauchenia. Hemiauchenia is an extinct genus of whether increasing hypsodonty indicates in- that ranged from the late Barstovian (ca. creased specialization for abrasive foods at the 13 Ma) to the late Rancholabrean (ca. 0.01 Ma) expense of browse, or an actual broadening of North American Land Mammal Ages (NAL-

᭧ 2003 The Paleontological Society. All rights reserved. 0094-8373/03/2902-0006/$1.00 PALEODIET OF HEMIAUCHENIA 231

MA) in (Honey et al. 1998). grasses and sedges; intermediate feeders, which This genus has been suggested to comprise have a composite diet of grasses and sedges, only browsers, according to morphological and browse. These three categories have been characteristics of the snout (Dompierre and adopted in much of the paleoecological liter- Churcher 1996), or to include intermediate ature for interpretation of paleoungulate diets, feeders with a preference for grasses, accord- and for use in paleoenvironment interpreta- ing to the presence of hypsodont teeth and tion (e.g., Janis 1988; Quade et al. 1992; So- abundant cementum (Webb 1974; Webb and lounias et al. 1995; MacFadden and Cerling Stehli 1995). This study uses stable carbon iso- 1996; Janis et al. 2000). In using these three cat- topes and measures of hypsodonty to deter- egories alone, much of the complexity in feed- mine the feeding strategy employed by Hem- ing in ungulates is obscured; for example, an iauchenia during the past 5 million years. The intermediate feeder does not necessarily have results are then used to assess whether the at- a diet midway between a browser and a graz- tainment of hypsodonty within the Lamini er. Hofmann and Stewart (1972) suggested evolved through the progression of browsing further subcategories within the three main to intermediate feeding to grazing, and categories to reflect some of this complexity. whether hypsodont animals are specialized Thus, concentrate selectors can be subdivided grazers. into tree and shrub foliage eaters and fruit and di- cot foliage eaters. Bulk and roughage feeders in- Background Information clude the subcategories roughage grazers, fresh As mentioned above, hypsodonty and the grass grazers, and dry region grazers. Within in- shape of the ungulate muzzle are but two termediate feeder are the subcategories prefer- morphological proxies used to interpret pa- ring grasses and preferring forbs, shrubs, and tree leodiet. Generally, more hypsodont animals foliage. However, these subcategories are sel- tend to feed on grasses and live in open hab- dom used in paleobiological studies because it itats. Because the spread of grasslands during generally is difficult to determine the percent the appears roughly coincident with of a particular forage type within the diet of widespread hypsodonty, it has been hypoth- an extinct ungulate. Whereas one can observe esized that hypsodonty evolved as a coevolu- the forage and droppings of modern ungu- tionary response to the spread of phytolith- lates, it is often difficult or impossible to link laden grasses, and as an adaptation to deal paleobotanical remains and/or coprolites to with grit and dirt that typically coats plants in particular extinct animals. However, as is ex- open habitats (McNaughton et al. 1985; Janis plained below, in a restricted geographical 1988, 1989, 1995; MacFadden 1997). With re- area in which the flora is relatively well spect to the shape of the muzzle in ungulates, known, the analysis of stable carbon isotopes grazers have a broad muzzle capable of feed- in the tooth enamel of extinct herbivores pro- ing on large quantities of low-lying forage, vides a means for determining the percentage and browsers generally have narrow muzzles of certain forage in the diet. This proxy can be for manipulating through branches to select used to distinguish browsers, grazers, inter- choice, succulent forage. Intermediate feeders mediate feeder with a preference for grasses generally have muzzle widths in between and sedges, and intermediate feeder with a (Janis and Ehrhardt 1988; Solounias et al. preference for browse. 1988; Dompierre and Churcher 1996). Carbon Isotopes and Diet. The carbon iso- Modern Ungulate Feeding Categories. Hof- tope values of fossil teeth are useful in paleo- mann and Stewart (1972) used forage com- diet studies because different photosynthetic position and stomach structure, to character- pathways impart different ratios of 13C/12Cin ize modern ungulate feeding strategy into different kinds of plants, which are ultimately three main types: concentrate selectors (brows- reflected in the animals that eat them. Plants ers), which focus feeding on flora other than can be grouped into three main photosyn- grasses and sedges (browse); bulk and roughage thetic pathways: C3,C4, and Crassulacean feeders (grazers), which concentrate feeding on Acid Metabolism (CAM). Tropical, warm-sea- 232 ROBERT S. FERANEC son sedges and grasses using the Hatch-Slack aceae, and up to 43% for Cyperaceae [Teeri photosynthetic pathway (C4) are enriched in and Stowe 1976; Teeri et al. 1980; Sage et al. the heavy carbon isotope (13C). Conversely, 1999]). Two studies of modern floral compo-

Calvin cycle plants (C3), including most sition on sites near fossil localities within this browse and high-latitude grasses, are en- study show that even though C3 grasses and riched in the light carbon isotope (12C). The sedges may be present and represent up to third pathway, the CAM pathway, is charac- 40% of the species richness of grasses, C3 teristic of succulents and incorporates inter- grasses are generally confined to wet and mediate ratios of 12Cand13C (O’Leary 1988; marshy areas and are not widespread on the Ehleringer et al. 1991; Ehleringer and Monson landscape (Easley and Judd 1990; Huffman 1993). Animals that feed upon these various and Judd 1998). Many of the fossil localities kinds of plants will reflect the isotope ratio within this study are suggested to have floras (13C/12C) ingested (DeNiro and Epstein 1978; similar to the interglacial floras of today Quade et al. 1992). The 13C/12C ratio of tooth (Webb 1991; Rich and Newsom 1995), and enamel is further enriched by a consistent models of past floras during glacial stages amount, which is about ϩ14‰ for the tooth would suggest the spread of grasslands and enamel of medium- to large-bodied mammals an increase in dominance of grasses and sedg-

(Cerling and Harris 1999). Although post-de- es using C4 photosynthesis due to decreasing positional diagenesis can overprint carbon CO2 levels (Webb 1991; Ehleringer et al. 1997; isotope values in bone (Schoeninger and Cowling 1999). This would suggest that per-

DeNiro 1982), tooth enamel is not prone to centages of C3 grasses in Florida are unlikely diagenetic alteration and thus reliably reflects to have been significantly greater during the isotope values derived from feeding (Quade et past, and because C4 browse is rare, it is un- al. 1992; Wang and Cerling 1994; Koch et al. likely that these percentages have significant- 1997). As a general guide, grazers are predom- ly changed. inantly C4 feeders, browsers are predomi- Materials and Methods nantly C3 foragers, and intermediate and

CAM feeders utilize both C3 and C4 plants. Definitions and Feeding Strategies. Grazers Care must be taken when interpreting carbon are strictly defined in this study as animals isotopic values in herbivore tissue because that eat grasses and sedges (Poaceae and Cy- some grasses, especially those above 43ЊNlat- peraceae) as at least 90% of their diet. Browsers itude, use the C3 pathway; some browse uses are considered here to have diets consisting the C4 pathway, especially in lower latitudes nearly exclusively of non-grasses and sedges, and drier climates; and animals that are strict that is browse (Ͼ90%). Intermediate feeders CAM feeders can show values similar to either eat both grasses and sedges, and browse (i.e.,

C3 or C4 feeders (Teeri and Stowe 1976; Stowe Ͼ10% grasses and sedges, and browse). This and Teeri 1978; O’Leary 1988; Tieszen et al. type of designation is appropriate because an- 1997). Because CAM flora is generally only atomical and physiological differences char- dominant in xeric habitats (Ehleringer et al. acterize animals that focus feeding on grasses 1991), it is assumed that Hemiauchenia did not and sedges and/or browse. Grazers, for ex- use this flora as a significant proportion of its ample, must deal with abundant abrasive phy- diet. toliths and grit from feeding close to the Florida as a Model Location. Florida is ideal ground, and accordingly develop strategies to for this study because (1) the flora eliminates deal with tooth abrasion. Browsers, on the many of the discrepancies that can occur other hand, ingest more anti-herbivory chem- when interpretation is based on isotopic val- icals such as tannins (McNaughton 1991; ues, and (2) because Hemiauchenia is abundant Heckathorn et al. 1999), which necessitate in late Tertiary through Quaternary deposits. strategies to deal with these secondary chem-

Nearly all present-day browse in Florida is C3 icals, but tooth abrasion offers less of a selec- (Ͼ97% [Stowe and Teeri 1978]), whereas most tive pressure than it does for grazers. The def- of the grasses and sedges are C4 (Ͼ63% for Po- initions used in this paper parallel the cate- PALEODIET OF HEMIAUCHENIA 233

not confined to the second through fourth pre- molars and third . These teeth are among the last ones to develop, mineralize, and erupt (Hillson 1986; Bryant et al. 1996 a,b). Sampling involved drilling 20–30 mg of pristine enamel powder off the tooth along a non-occlusal surface parallel to the growth axis and across its entire length using a 0.3- mm inverted cone carbide drill bit and a var- iable speed Dremel ௢ rotary tool. The powder was first collected and treated with 35% hy- drogen peroxide for 24 hours to remove or- ganics. It then was decanted and washed with distilled water and soaked in 0.1 N acetic acid for another 24 hours to remove any diagenetic carbonate. The following day it was again de- FIGURE 1. Fossil localities in Florida of the Hemiauchenia samples used in this study. Items in parentheses refer to canted and washed with distilled water, the number of specimens from the locality and to the rinsed with 100% ethyl alcohol, and dried North American Land Mammal Age. Abbreviations as follows: H ϭ Hemphillian, B ϭ , I ϭ Irvington- overnight. ian, R ϭ Rancholabrean. After treatment, the samples were analyzed by using an ISOCARB automated carbonate preparation system attached to a Micromass gories of Hofmann and Stewart (1972) for ease Optima gas source mass spectrometer within in comparison with modern ungulate analogs the Department of Earth and Ocean Sciences and other paleoecological studies. Where pos- at the University of California, Santa Cruz. sible the subcategories prefers grasses and sedges The ϳ1-mg samples were dissolved in 100% and prefers browse similar to Hofmann and phosphoric acid at 90ЊC to create CO2. The re- Stewart (1972) are also used for intermediate sults are expressed in standard ␦-notation: X feeders. ϭ [(Rsample/Rstandard) Ϫ 1] ϫ 1000, where X is Stable Isotope Analysis. Hemiauchenia molars the ␦13C value, and R ϭ 13C/12C. All isotope were obtained from the Vertebrate Paleontol- values are reported relative to V-PDB. The pre- ogy collection at the Florida Museum of Nat- cision for the analysis was Ϯ0.1‰. A total of ural History (FLMNH) and include four spe- 31 samples were collected, prepared, and an- cies: H. vera, H. blancoensis, H. seymourensis, alyzed along with the data for 19 samples ob- and H. macrocephala. The teeth range in age tained from the published literature (Mac- from the latest Hemphillian (ca. 5 Ma) to the Fadden and Cerling 1996; Feranec and Mac- latest Rancholabrean (ca. 10 Ka) NALMAs Fadden 2000). Mean differences in Hemiauch- and were taken from sites extending through enia between NALMAs were compared by the entire peninsula of Florida (Fig. 1). The post hoc LSD tests, which are similar to t-tests ages of the included localities were deter- but take into account multiple comparisons. mined biochronologically by assignment to Statistical analyses were run on Microsoft Ex- North American Land Mammal Ages (Lun- cel 2000 and SPSS Student Version 8.0 for Win- delius et al. 1987; Woodburne 1987; Mac- dows, with significance set at p Ͻ 0.05. Fadden and Cerling 1996). The Leisey Shell Pit Carbon Isotope Values in Paleoecology. As locality has also been paleomagnetically dat- noted above, herbivores will reflect the carbon ed at 1.5 Ma (MacFadden 1995). isotope values of plants ingested. Modern C3 The general method for stable isotope sam- plants—trees, shrubs, and high-latitude pling followed MacFadden and Cerling (1996) grasses—have a carbon isotope value of and Koch et al. (1997). Because the goal of the Ϫ27.0‰ Ϯ 3.0‰, whereas modern C4 study was to recognize the feeding strategy of plants—tropical sedges and grasses—have a adult animals, sampling focused on but was mean isotopic value of Ϫ13.0‰ Ϯ 2.0‰ 234 ROBERT S. FERANEC

(O’Leary 1988; Quade et al. 1992; Koch et al. numerator, height. Because of wear and 1998). Because of the ϩ14.0‰ fractionation small sample sizes, these measurements are from plant material to tooth enamel in large intended to show that Hemiauchenia was hyp- herbivores (Cerling and Harris 1999), modern sodont but not to show the level of hypsodon-

C3 feeders will show enamel carbon isotope ty for any particular species or at any partic- values between Ϫ16.0‰ and Ϫ10.0‰, where- ular time. Relative degree of hypsodonty as modern C4 feeders display isotopic values among species is provided by Webb (1974). between Ϫ1.0‰ and ϩ3.0‰. These enamel Modern Camelids and Modern Analogs. Un- isotope values are based on the ␦13C value of derstanding the diets of modern camelids aids the modern atmosphere, which has decreased in determining the feeding strategy of Hem- from about Ϫ6.5‰ to about Ϫ8.0‰ as a result iauchenia. Modern camelids can be placed of fossil fuel burning over the last two hun- within three genera and up to six species: Ca- dred years (Friedli et al. 1986; Marino and melus (including C. bactrianus and C. dromedar- McElroy 1991; Marino et al. 1992). Because ius), (including L. guanicoe, L. glama,and ␦13C values of past glacial and interglacial pe- L. pacos), and Vicugna (including V.vicugna). It riods are different from those of today, fossil is still uncertain whether the two identified enamel isotope values are about 0.5‰ to 1.3‰ species of Camelus or the three species of Lama more positive than in the modern taxa (Koch are conspecific (Nowak 1999). Because of these et al. 1998). For fossil enamel then, a diet of taxonomic similarities and the similarity in pure C3 plants would not have an isotopic val- morphology and ecology between the modern ue more positive than Ϫ8.7‰, and a diet of species (Nowak 1999), I treat them on the ge- pure C4 plants would not have an isotopic val- neric level. Studies on modern Camelus sug- ue more negative than Ϫ0.5‰. Using these gest that it is mainly a browser feeding pre- values as a continuum between 100% C3 feed- dominantly, if not solely, on trees and shrubs, ing and 100% C4 feeding, values more nega- but is capable of feeding and subsisting on a tive than Ϫ7.9‰ are interpreted to indicate significant quantity of grasses (Ͼ30%) when primarily browsing (Ͻ10% C4 diet), values necessary (Gauthier-Pilters 1984; Newman more positive than Ϫ1.3‰ are interpreted to 1984; Migongo-Bake and Hansen 1987; Koh- signal primarily grazing (Ͻ10% C3 diet), and ler-Rollefson 1991; Nowak 1999). Camelus is values between Ϫ7.9‰ and Ϫ1.3‰ result therefore classified as an intermediate feeder from intermediate feeding strategies. with preference for browse. Modern Lama has Hypsodonty Measurements. Hypsodonty mea- been suggested to be an ‘‘adaptable mixed surements for Hemiauchenia teeth were taken on feeder’’ (Puig et al. 1996: p. 221) showing a specimens at the FLMNH and compiled from the preference for feeding on grasses, but fully published literature (Webb 1974; Webb and Stehli able to feed on browse (Puig et al. 1996, 1997; 1995). Most measurements come from second Fraser 1998, 1999; Nowak 1999). Lama is clas- lower molars, and when possible the same sified here as an intermediate feeder with teeth were sampled isotopically. Measure- preference for grasses and sedges. Koford ments of crown height and width were taken (1957) suggested that the main food of the Vi- on teeth that were relatively unworn, and rep- cugna is grass, but that other forage such as resent the greatest height and width for each forbs and the legume Astragalus was a prized tooth. Tooth crown measurements (height and food when it was, though rarely, available. Vi- width) for extant camelids, Camelus, Lama,and cugna is classified here as a grazer. Isotopical- Vicugna, were acquired from the Museum of ly, all modern camelid genera would be ex-

Vertebrate Zoology (MVZ) at the University of pected to exhibit a C3 diet. This is because C3 California, Berkeley. The Hypsodonty Index grass genera predominate where camelids live (HI) was calculated as HI ϭ Crown Height/ (Koford 1957; Puig et al. 1996, 1997; Fraser Crown Width. Even though relatively unworn 1998, 1999; Sage et al. 1999). teeth were measured when possible, the HI This study also uses a modern analog com- represents a conservative estimate because parison similar to the Extant Phylogenetic any wear or incomplete eruption reduces the Bracket (EPB) method to determine if HI is an PALEODIET OF HEMIAUCHENIA 235

FIGURE 2. Stable carbon isotope values of Hemiauchenia from the Hemphillian through the Rancholabrean of North America. osteological correlate that may be ‘‘causally Within the Quaternary of Florida, Hemiauch- related’’ to obligate grazing (Witmer 1995: p. enia is represented by 39 specimens. Fifteen Ir- 23). The comparison in this study differs from vingtonian samples were analyzed, yielding a an EPB comparison in that a cladistic analysis mean ␦13C value of Ϫ8.0‰ and a standard de- with hypsodonty characters was not complet- viation of 2.9‰. The isotopic values ranged ed and is beyond the scope of this study. The from Ϫ3.2‰ to Ϫ12.4‰. Of the 15 specimens, modern analog comparison should nonethe- five specimens had values suggesting the in- less work in the same fashion as the EPB meth- corporation of C4 forage and three had isoto- odology. Therefore, if hypsodonty is a good pic values suggesting feeding on more than osteological correlate for obligate grazing 50% C4 (Fig. 2, Appendix 1). Twenty-four Ran- within fossil Lamines, then all taxa that have cholabrean specimens were sampled, and high-crowned teeth (the osteological corre- demonstrated a mean ␦13C value of Ϫ8.3‰ late) should be grazers, or at least intermedi- and a standard deviation of 4.3‰. The range ate feeders with preference for grasses and in isotopic values was from ϩ0.4‰ to sedges (the behavior or ecology). The stable Ϫ14.0‰. Of the 24 specimens, nine had values isotope value of fossil enamel can be used as suggesting the incorporation of some C4 for- an independent indicator for grazing as sug- age into the diet. Five of these specimens had gested above. In this study, I use the phylog- values suggesting feeding on 50% or more C4, eny proposed by Honey et al. (1998), (Camelus, three of which indicated 100% C4 feeding. The

(Hemiauchenia,(Lama, Vicugna))), where the three specimens feeding on 100% C4 were fossil genus Hemiauchenia is bracketed by the from the latest Rancholabrean (ca. 11 Ka [Em- extant genera Camelus and Lama-Vicugna. slie and Morgan 1995]) Cutler Hammock lo- cality of southern Florida. Results Post hoc LSD tests did show significant dif- Stable Carbon Isotope Analysis. Of the 11 ferences between the Blancan and Irvingtoni- specimens of Hemiauchenia sampled from the an (p ϭ 0.032), and between the Blancan and Tertiary of Florida, one was from the Hem- the Rancholabrean (p ϭ 0.036). phillian and ten were from the Blancan. The Hypsodonty Indices. The Hypsodonty In- Hemphillian specimen, from the Bone Valley dex (HI) in the Hemphillian for the single Formation in Florida had a ␦13C value of specimen of Hemiauchenia was 1.36 with a Ϫ5.6‰ (Fig. 2, Appendix 1). The Blancan crown height of 18.1 mm and width of 13.3 specimens had a mean ␦13C value of Ϫ11.3‰ mm (Table 1). The Blancan specimens had a and a standard deviation of 2.3‰. The isoto- mean HI of 1.03 with a mean height and width pic values ranged from Ϫ8.1‰ to Ϫ14.7‰. of 15.4 mm and 15.0 mm, respectively. The Ir- 236 ROBERT S. FERANEC

TABLE 1. Hypsodonty measurements for Hemiauchenia from Florida. Most measurements were taken directly from the literature (Webb 1974; Webb and Stehli 1995). The Leisey Shell Pit 1A data are means from 18 specimens. Crown height measurements were taken from the base of the enamel to the occlusal surface of the individual tooth. Ab- breviations: m1 ϭ lower first molar; m2 ϭ lower second molar.

Specimen Crown Localities number Tooth height (mm) HI Hemphillian Bone Valley UF 23946 m1 18.1 1.36 Blancan Inglis 1A UF 18223 m2 12.3 0.78 Macasphalt Shell Pit UF 104500 m2 18.5 1.31 Irvingtonian Leisey Shell Pit 1A 18 specimens m2 35.1 2.22 Rancholabrean Cutler Hammock UF 206866 m2 21.5 1.82 Waccasassa River UF 47439 m2 30.7 2.24

vingtonian specimens had a HI of 2.22 with a through the Quaternary of Florida suggest height of 35.10 mm and a width of 15.80 mm. that it most commonly fed as a browser but The Rancholabrean specimens had a mean HI was fully capable of having a varied diet in- of 2.04 with a mean height of 26.1 mm and a clusive of grasses and sedges. Hemiauchenia is mean width of 12.75 mm. therefore classified here as an intermediate Within the extant camelids, the Camelus feeder with preference for browse. Those spec- sample had a mean HI of 1.48 with a mean imens with more positive ␦13C values conceiv- height of 29.9 mm and a mean width of 20.2 ably were eating C4 browse, but this is unlikely mm (Table 2). The Lama sample had a mean HI because Ͻ3% of browse species in Florida are of 1.30 with a mean height of 14.6 mm and a C4 today, and the same would have been the mean width of 11.6 mm. The Vicugna sample case through the time spanned by this study. had a mean HI of 1.60 mm with a mean height Comparison with Previous Isotopic Studies. of 14.2 mm and a mean width of 9.3 mm. The The data presented here for Hemiauchenia are HI of both the modern and the fossil taxa iden- similar to those presented by Feranec and tifies these animals as hypsodont, especially MacFadden (2000), which showed a signifi- in view of the fact that wear or incomplete cant difference in carbon isotope values across eruption means the values for HI are conser- the Blancan/Irvingtonian boundary. Feranec vative. and MacFadden (2000) further suggested a change in feeding strategy from a pure brows- Discussion ing strategy to an intermediate feeding strat- The stable carbon isotope values displayed egy. The data here suggest that Hemiauchenia by Hemiauchenia from the Late Tertiary maintained a predominantly browsing feed-

TABLE 2. Hypsodonty measurements for the extant camelid genera Camelus, Lama,andVicugna. Abbreviations: m1 ϭ lower first molar; m2 ϭ lower second molar; L ϭ left; R ϭ right.

Specimen Crown Species number Tooth height (mm) HI Camelus dromedarius MVZ 101026 Lm1 26.8 1.37 Camelus bactrianus MVZ 74673 Rm1 33.0 1.59 Lama sp. MVZ 119831 Lm2 13.6 1.11 Lama sp. MVZ 116807 Rm2 13.1 1.16 Lama guanicoe MVZ 116318 Rm2 17.2 1.51 Vicugna vicugna MVZ 184198 Rm2 11.8 1.13 Vicugna vicugna MVZ 116208 Lm2 16.6 2.05 PALEODIET OF HEMIAUCHENIA 237 ing strategy but included more grasses and sedges in the diet in the Quaternary. This re- sult may indicate a change in the flora occur- ring across the Blancan/Irvingtonian bound- ary to a more open habitat and a higher dom- inance of grasses and sedges. Alternatively, the result may indicate only sampling bias, with more closed-canopy sites sampled in the Blancan, and a wider range of habitats sam- pled in the Irvingtonian and the Ranchola- brean. Because the localities from these NAL- MAs covers a wide geographical range (Fig. 1), a change in flora seems the more probable explanation. Modern Analog Comparison. All of the ca- melid species, both fossil and extant, had HI above 1.0, which is consistent with feeding on FIGURE 3. Phylogenetic relationships of Hemiauchenia a higher percentage of grasses and sedges. with the mean Hypsodonty Index (HI) ‘‘measured’’ in Modern observations of extant camelids have this study and feeding strategy of the genera included. Feeding data on the extant genera are from modern shown them to be either intermediate feeders studies, and those for Hemiauchenia come from stable (Camelus and Lama) or pure grazers (Vicugna). carbon isotope values and knowledge of the Floridian The stable carbon isotope evidence and a high flora. These HI values indicate that each genus is hyp- sodont; they are not intended to show the exact HI val- HI suggest that Hemiauchenia was a hypsodont ues for specific taxa. Because these genera are all hyp- intermediate feeder with a preference for sodont but are not all grazers, hypsodonty is not caus- browse (Table 1, Fig. 2). This result is similar ally related to grazing and should not be used by itself to the findings of Dompierre and Churcher as an indicator of paleodiet. (1996), whose study used muzzle shape to de- termine feeding strategy and suggested that gested to have increasing hypsodonty in that Hemiauchenia was a ‘‘browser or browser-like order (Webb 1974), it might be inferred that intermediate feeder, similar to the Bactrian the differences seen in the carbon isotope val- camel’’ (Dompierre and Churcher 1996: p. ues reveal species-level ecological differences 146). This study suggests that hypsodonty is and that hypsodonty between species does re- not a good osteological correlate and not flect those changes. This cannot be the case, ‘‘causally related’’ to obligate grazing for an- however, because the least hypsodont taxa cient taxa within the Lamini (Fig. 3). Hypso- within this study, H. vera, has a carbon isotope donty has been shown to be a spurious cor- value (Ϫ5.6‰) indicating an intermediate relate to obligate grazing in previous studies feeding diet, and the more hypsodont species on certain equid and proboscidean taxa as H. blancoensis has isotopic values indicating a well (Cerling et al. 1999; MacFadden et al. pure C3 feeding strategy, i.e., browsing (Ap- 1999). These results are consistent, however, pendix 1). with the hypothesis that the ancestral ungu- Links between Hypsodonty and Grazing. The late feeding state is browsing, which then diets of Hemiauchenia and many other species, changes through intermediate feeding to the which were based on the HI, have been used derived grazing strategy (Fig. 3) (Perez-Bar- to infer environment and interpolate primary beria et al. 2001). productivity in Nebraska (Janis et al. 2000). Ecology of Hemiauchenia Species. Because Hemiauchenia species were suggested in that this study includes the species H. vera, H. blan- study to be mesodont, and mesodont animals coensis, H. seymourensis,andH. macrocephala, ‘‘had a wider array of diets but for the most which occur in Florida during the Hemphil- part depended on grass to a greater extent lian, Blancan, Irvingtonian, and Ranchola- than did browsers’’ (Janis et al. 2000: p. 7901). brean, respectively, and these species are sug- Those results are in accord with the results of 238 ROBERT S. FERANEC this study. However, given the wide range in mals teeth in the few days before they died. diet possible, as shown by the carbon isotope These studies are beyond the scope of this pa- evidence, the link between hypsodonty and per but are underway by other investigators. environment or amount of primary productiv- ity in a particular area becomes weaker. Conclusions The increase in number of taxa having hyp- Characterizing the diets of extinct herbi- sodont dentitions has been used to suggest vores is important before further inferences that C3 grasslands became more widespread about paleoenvironment can be made. Clas- in the early Miocene (ca. 18 Ma [McNaughton sifying an or a group of animals into et al. 1985; Janis 1989; MacFadden 1997]). New categories based upon a single specialization studies lend credence to this interpretation by in morphology can be a useful approximation suggesting that the abundance of grass phy- of ecological requirements. For maximal util- toliths in sediment pushes the spread of grass- ity, however, a full understanding of the niche lands back 10 Myr before the increase in taxa breadth in which the specialization is used with hypsodont teeth (Stro¨mberg et al. 2000; must be ascertained. To accomplish this, mul- Stro¨mberg 2002). Because the results reported tiple lines of evidence for determining the diet here for Hemiauchenia, as well as information of the extinct animal must be used. about equids and proboscideans (Cerling et al. The data presented here for Hemiauchenia 1999; MacFadden et al. 1999), indicate that from the Late Tertiary through the Quaternary hypsodonty is not always correlated with in Florida show that even though it had hyp- feeding on significant quantities of grasses sodont teeth, it most commonly was an inter- and sedges, it may be that the development of mediate feeder with a preference for browse. The hypsodonty primarily reflects a diet that be- modern analog comparison suggests that came more generalized to include the newly hypsodonty is not causally related to obligate widespread grasslands, rather than a strict grazing in this genus of llama, or within the shift from browsing to grazing. Lamini in general. The results are consistent Rates of Morphological Evolution and Diet. with the findings of Dompierre and Churcher This example from Hemiauchenia highlights (1996), who inferred intermediate feeding the disjunction between the evolution of mor- from muzzle width, and with the hypothesis phological characteristics, such as hypsodon- that feeding evolved from browsing through ty, and the current use of the morphology in intermediate feeding and ultimately to graz- determining an animal’s ecology. In this par- ing (Perez-Barberia et al. 2001). Because hyp- ticular example, the hypsodont morphology sodonty tells little about floral species that does not appear to reflect a specialization that were eaten, it is only a coarse tool to interpret restricts the animal to a grazing or primarily feeding ecology in fossil taxa: hypsodonty grass-dominated diet. This is not to say that may make grazing possible, but it does not hypsodont teeth did not evolve as an adapta- unequivocally mean the animal was a ‘‘graz- tion to feeding on grasses or on gritty mate- er.’’ In fact, hypsodonty in Hemiauchenia ap- rial, but to suggest that previous feeding strat- pears to have widened its niche breadth rela- egies on browse were not necessarily aban- tive to ancestral browsers. Whether such an doned. This study demonstrates that a spe- interpretation reflects a general relationship cialized dental morphology may in fact between attainment of a specialization and broaden the ecological niche that the organ- widening of niche space remains to be tested isms occupy, rather than restrict the niche. by further studies on a variety of taxa. Therefore, interpretations based on assump- tions that all specialized morphologies indi- Acknowledgments cate a restricted ecology deserve further scru- This study was improved thanks to discus- tiny using complementary lines of evidence. sions and comments from A. D. Barnosky, B. An important area of future investigation J. MacFadden, C. M. Janis, D. Fox, J. Quade, H. would be microwear studies to gain insights Dompierre, M. A. Carrasco, L. Witmer, S. D. into the nature of the food that abraded ani- Webb, E. B. Davis, P. D’Girolamo, S. S. B. Hop- PALEODIET OF HEMIAUCHENIA 239 kins, D. Ruez, and K. C. Smith. Funding was ———. 1999. A comparison of the diet composition of guanacos (Lama guanicoe) and sheep when grazing swards with differ- provided by Sigma Xi Grants-in-Aid-of-Re- ent clover: grass ratios. Small Ruminant Research 32:231–241. search, the Department of Integrative Biology, Friedli, H., H. Lo¨tscher, H. Oeschger, U. 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Sample n ϭ Hemphillian Blancan Blancan Blancan Blancan Blancan Blancan Blancan Blancan Blancan Blancan Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Irvingtonian Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean molar; P ϭ denotes upper tooth; lower case specimens. ? in species column refers to suspected right side; M upper case ϭ Location Age Hemiauchenia left side; R ϭ Bone Valley Santa Fe River Santa Fe River Santa Fe River Santa Fe River Santa Fe River Macasphalt 1A Macasphalt 1A Santa Fe River Lehigh Acres Lehigh Acres Inglis 1A Inglis 1A Inglis 1A Inglis 1A Inglis 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Leisey 1A Haile 8A Cutler Hammock Cutler Hammock Cutler Hammock Waccasassa River Waccasassa River Waccasassa River Waccasassa River Waccasassa River Waccasassa River Waccasassa River Waccasassa River C value from 13 ␦ lement Appendix 1 rp4 M fragment M fragment m3 M fragment M/P rm3 M fragment m3 RM1 RM1 LP4 lm3 lm3 rm3 LM3 lm3 rm3 lm3 LP4 RP4 rm3 LP3 RM RP4 RM3 M rp4 lp4 rp3 m3 m3 fragment m3 m3 P4 M M M able and sampled. L ocality, NALMA, and 23946 17693 17518 45284 18223 17522 64219 80053 64315 83964 84239 85085 80737 83965 56589 47443 47442 47445 47443 47544 47543 47542 47545 uncataloged uncataloged uncataloged uncataloged 104500 100096 V-5107 uncataloged uncataloged uncataloged 142321 132000 uncataloged uncataloged uncataloged element sampled, l ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? element was found or age of the element. In element abbreviations, ? vera blancoensis blancoensis blancoensis blancoensis blancoensis blancoensis blancoensis blancoensis blancoensis blancoensis macrocephala macrocephala macrocephala macrocephala macrocephala seymourensis seymourensis seymourensis seymourensis seymourensis seymourensis seymourensis seymourensis seymourensis seymourensis macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala umber Species UF number E umber, species, UF catalog number, Sample n Sample n beginning with F&MCF and MCF&C refer to the previously published data of Feranec and MacFadden (2000) and MacFadden and Cerling (1996), respectively RSF0029 F&MCF, 2000(RSF-60) F&MCF, 2000(RSF-61) F&MCF, 2000(RSF-62) F&MCF, 2000(RSF-63) MCF&C, 1996–72 RSF0035 RSF0043 RSF0048 RSF0053a RSF0053b RSF0030 RSF0031 RSF0032 RSF0033 RSF0034 F&MCF, 2000(RSF-19) F&MCF, 2000(RSF-20) F&MCF, 2000(RSF-21) F&MCF, 2000(RSF-22) F&MCF, 2000(RSF-23) RSF0036 RSF0037 RSF0038 RSF0039 RSF0040 RSF0045 MCF&C, 1996–97 RSF0023 RSF0024 F&MCF, 2000(RSF-43) F&MCF, 2000(RSF-44) F&MCF, 2000(RSF-45) F&MCF, 2000(RSF-46) F&MCF, 2000(RSF-47) F&MCF, 2000(RSF-101) F&MCF, 2000(RSF-102) F&MCF, 2000(RSF-103) species based on the locality in which the tooth; ‘‘fragment’’ means that only a partial piece of the tooth was avail 242 ROBERT S. FERANEC C 9.2 9.8 7.7 2.2 9.2 7.9 9.0 5.0 13 11.7 14.0 13.5 10.7 Ϫ Ϫ Ϫ Ϫ Ϫ Ϫ Ϫ Ϫ ␦ Ϫ Ϫ Ϫ Ϫ Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Rancholabrean Location Age Reddick 1 Reddick 1 Reddick 1 Waccasassa River Waccasassa River Waccasassa River Waccasassa River Withlacoochee River Withlacoochee River Withlacoochee River 7A Paines Prairie Dredge Sarasota Intercoastal Waterway lement m3 M RM3 M fragment m3 M M fragment fragment M RM3 M M 2855 8902 47502 47440 47503 47501 46828 46827 18028 18334 11503 uncataloged ? ? ? ? ? ? ? ? ? ? macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala macrocephala umber Species UF number E . Continued. Sample n Appendix 1 RSF0025 RSF0026 RSF0027 RSF0049 RSF0050 RSF0051 RSF0052 RSF0041 RSF0042 RSF0044 RSF0046 RSF0047