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Preliminary data on the diet and habitat preferences of Capromeryx Mexicana (Mammalia: antilocapridae) from the late Pleistocene of Cedral, San Luis Potosi, Mexico.

Antilocapridae is a family within the order Artiodactyla which is currently represented by only one species of pronghorn, Antilocapra americana, distributed from southern Canada to northern Mexico (O'Gara, 1978). During the Pleistocene, however, a greater diversity of genera and species of Antilocapridae inhabited North America (Davis, 2007). Six species of antilocaprids have been proposed to have inhabited Mexico in addition to Antilocapra americana: Tetrameryx tacubayensis, Tetrameryx shuleri, Tetrameryx mooseri, Stockoceros conklingi, Capromeryx minor, and Capromeryx mexicana (Ferrusquia-Villafranca et al., 2010; Bravo-Cuevas et al., 2013). Fossil remains of C. mexicana have been reported from few Mexican localities, and it has been suggested by some researchers to have fed on grasses and Asteraceae plants, based on molar morphology, and the assumption that it inhabited grasslands (Johnson et al., 2006). Given the lack of knowledge about the diet and habitat of this rare antilocaprid species, we present preliminary data on its feeding ecology and habitat preferences using two methodological approaches--mesowear analysis and carbon and oxygen isotopic ratio assays--for three individuals from the late Pleistocene locality of Cedral, San Luis Potosi, Mexico (23[degrees]49'N, 100[degrees]43'W; 1,700 meters above sea level). Capromeryx mexicana has a very limited fossil record in Mexico. In eight excavation seasons at Cedral, from 1977-1991, only three upper molars were recovered (Alvarez et al., 2012; Mirambell, 2012). These specimens form the basis of this report.


We collected a bulk dental enamel sample (20 mg) from specimens DP3322 and DP3328, which are on deposit in the Paleontological Collection, Laboratorio de Arqueozoologia "M. en C. Ticul Alvarez Solorzano," Subdireccion de Laboratorios y Apoyo Academico, Instituto Nacional de Antropologia e Historia, Mexico City. We prepared the samples following the method of Koch et al. (1997) and processed them at Laboratorio de Isotopos Estables, Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Mexico City, where they were analyzed following the method described by Revesz and Landwehr (2002) and normalized in accordance to Coplen (1988), Coplen et al. (2006), and Werner and Brand (2001). We compared the isotopic value of carbon we obtained to those proposed by MacFadden and Cerling (1996). Values of [[delta].sup.13]C ranging from -19% to -9% are typical of animals that feed on [C.sub.3] plants such as trees and shrubs. Animals that eat [C.sub.4] plants, such as many grasses, show values that range from -2% to 2%, and carbon isotopic values of -9% to -2% are typical of mixed-feeding animals. Subsequently, we compared the carbon and oxygen isotopic values obtained for C. mexicana to those of tapirs (Tapirus species) and horses (Equus conversidens) from Cedral (Perez-Crespo, 2013), which have been considered as browsers and grazers, respectively.

We collected mesowear data for the three specimens that were available for study, DP3322, DP3328, and DP4310, which are on deposit in the Paleontological Collection, though DP4310 was not available for the stable isotopes assays. Each is in a middle stage of wear. The variables considered included the degree of relief of the cusps (high or low) and the shape of the sharpest cusp (whether anterior or posterior), which was scored as sharp, rounded, or blunt (Fortelius and Solounias, 2000; Franz-Odendaal and Kaiser, 2003). For each studied specimen, we took digital photographs of the buccal side of the tooth using a Sony Cyber-Shot DSC-H9 digital camera (Sony Electronics Corporation, San Diego, California). To determine cusp relief, we measured the depth of the valley between the paracone and metacone cusps as well as the anteroposterior length of each tooth using the computer software ImageJ 1.47 (Rasband, 2013). We took these measurements three separate times for each tooth and calculated the average with the objective of reducing measurement error. We scored a tooth as having high cusps if the cusp height index (i.e., valley depth divided by the anteroposterior length of the tooth) was greater than 0.10 (Fortelius and Solounias, 2000), and we scored cusp shape by direct observation of the specimens. We recorded the frequency of the mesowear variables as well as the mesowear score for the study sample. The mesowear score combines cusp relief and shape into a single value that ranges from 0 (high relief and sharp cusps) to 3 (low relief and blunt cusps; e.g., Rivals and Semprebon, 2006; Rivals et al., 2007). We compared the average mesowear score for C. mexicana from Cedral to data reported for modern ungulate species (with the exclusion of the minute, abraded brachydont ungulates) classified into three dietary categories: browsers, mixed feeders, and grazers (as reported by Fortelius and Solounias, 2000).

The [[delta].sup.13]C mean value is -7.2% and the mean oxygen isotopic value is -4.5% (DP3322 [[delta].sup.13]C = -5.7%, [[delta].sup.18]O = -4.6%; DP3328 [[delta].sup.13]C = -8.8%, [[delta].sup.18]O = -4.3%). The graph showed that C. mexicana forms an independent group from horses and tapirs (Fig. 1).

Capromeryx mexicana specimens analyzed for mesowear showed high cusps with either sharp or rounded cusp morphologies (DP3322 and DP4310 show high and sharp cusps whereas DP3328 displays high and rounded cusps), resulting in a mean mesowear score of 0.33. This value is located within the mesowear range of extant browsing ungulates and on the lower range of extant mixed feeders (Fig. 2) reported in Fortelius and Solounias (2000); however, due to the reduced sample size a statistical assessment is precluded. The mean mesowear score of C. mexicana from Cedral also plots on the lower range of a set of fossil antilocaprid species, subfamily Antilocaprinae and is identical to the mesowear score of Stockoceros onusrosagris from the Rancholabrean of Papago Springs Cave, Arizona, United States (Fig. 2) published by Semprebon and Rivals (2007).


The results of both methods indicate that the three studied individuals of Capromeryx mexicana from Cedral were [C.sub.3]-[C.sub.4] mixed feeders (DP3322, DP3328, DP4310) with one individual, DP3328, showing a greater proportion of [C.sub.3] plants in its diet. These results differ from the proposal by Johnson et al. (2006), who suggested that these animals were specialized in the consumption of grasses. Also, taking into account that mesowear and stable isotope analyses show the dietary habits of an individual at different stages of its life, the finding that two individuals, DP3328 and DP3322, were identified as mixed feeders by both analyses suggest that they maintained a mixed-feeding diet throughout their life. This is concordant with the results reported for other species of antilocaprids by Connin et al. (1998), Coltrain et al. (2004), Rivals and Semprebon (2006), Semprebon and Rivals (2007), and Bravo-Cuevas et al. (2013), who found that diet in these animals was flexible as they could feed on leaves of trees and shrubs but also ingested grasses or other herbaceous plants.

Feranec and MacFadden (2006) pointed out that most negative carbon and oxygen isotopic values show the presence of forested, humid areas while positive values indicate grasslands and arid areas. Capromeryx mexicana has intermediate values of [[delta].sup.13]C and [[delta].sup.18]O when compared with tapirs (Tapirus species) and horses (Equus conversidens). On the other hand, Pleistocene pronghorns have intermediate isotopic values between two species, horses and tapirs, which, based in the proposal by Feranec and MacFadden (2006), show that in Cedral there existed a heterogeneous vegetation, and not a unique type, and that specimens pertaining to C. mexicana at this locality inhabited a transition zone between forest and grassland, which is different from the proposal by Johnson et al. (2006) who suggested that this species lived in grasslands.

The palynological record for Cedral shows the existence of Cupressus, Juniperus, and Taxodium species, grasses, Asteraceae as well as Chenopodiaceae plants, and cacti (Sanchez-Martinez and Alvarado, 2012), which suggests that in this zone an open forest was established such as those found in other regions of Mexico (Caballero et al., 2010).

Capromeryx mexicana from Cedral had a [C.sub.3]-[C.sub.4] mixed feeding dietary behavior, showing that this species was more generalist than specialist; its habitat was an open forest with interspersed grasslands. However, it is important that more specimens are examined to better assess the dietary spectrum of this rare pronghorn species.

We thank the Consejo de Arqueologia from Instituto Nacional de Antropologia e Historia for granting the permit to obtain the enamel samples from the pronghorn specimens. Thanks are also due to the Consejo Nacional de Ciencia y Tecnologia de Mexico (CONACYT scholarships 310423 and 132620) and the University of Calgary for supporting this project. We also extend our gratitude to the Laboratorio de Isotopos Estables from the Institute of Geology, UNAM, as well as to R. Puente-Morales for their assistance analyzing the samples.


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Submitted 9 October 2015 Acceptance recommended by Associate Editor, Troy Ladine, 19 February 2016.

Victor Adrian Perez-Crespo, * Christian R. Barron-Ortiz, Joaquin Arroyo- Cabrales, Pedro Morales-Puente, Edith Cienfuegos-Alvarado, Francisco J. Otero

Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Circuito de la Investigacion Cientifica S/N, Ciudad Universitaria, Del. Coyoacan, 04519, Mexico, D. F. (VAPC, PMP, ECA, FJO)

Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, AB, T2N 1N4, Canada (CRBO)

Laboratorio de Arqueozoologia "M en C. Ticul A' lvarez Solorzano," Subdireccion de Laboratorios y Apoyo Academico, INAH, Moneda 16 Col. Centro, 06060 M'exico, D. F. (JAC)

* Correspondent:
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Author:Perez-Crespo, Victor Adrian; Barron-Ortiz, *.Christian R.; Arroyo-Cabrales, Joaquin; Morales-Puente,
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1MEX
Date:Jun 1, 2016
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