Díaz-Sibaja et al.—Mexican Bison antiquus diet 92(6):1130–1139
and nonstrict grazer) of the Bison antiquus samples of this study, we performed a cluster analysis with 27 model species with known dietary preferences taken from the original Fortelius and Solounias (2000) database with the variables Per-High, Per- Sharp, and Per-Blunt (percentages of high, sharp, and blunt cusps in the total sample), using the complete linkage (without standardization of the data) clustering method, and Euclidean distance for scaling (Fortelius and Solounias, 2000; Franz- Odendaal and Kaiser, 2003; Clauss et al., 2007). In addition to the cluster analysis, we transformed the
original Fortelius and Solounias (2000) database to the univariate 0 −3 scale of mesowear to compare the signatures of our three samples of Bison antiquus with known dietary categories (browser, grazer, and mixed feeder) of model and extinct Bison species as follows: high and sharp cusps were assigned a 0 score, high and rounded a 1, low and sharp or low and rounded a 2, and blunt cusps were assigned a 3 score (Rivals et al., 2007b). Additionally, we performed Pearson’s chi- squared tests (α=0.05) to compare the mesowear patterns of the 0− 3 univariate scale (Fortelius and Solounias, 2000; Rivals et al., 2007b) and the mesowear III (Solounias et al., 2014) with our samples, to determine the similarities in the wear patterns with the model dietary groups (i.e., browser, grazer, or mixed feeder).
Although we recognize that relief and cusp shape can be
affected by the creep of phylogenetic signal (Fortelius and Solounias, 2000), independent data suggest that when a phyloge- netic control is introduced, the correct classification of a samples improves by only one percent (Fraser and Theodor, 2011), and thus, we did not consider use of any phylogenetic control. Finally, to predict the dietary guild with more accuracy, we
combined the data of extended mesowear (0−3 univariate scale) and mesowear III (scores of the mesial, distal, and j-junction) to perform a discriminant analysis (see Supplemental data set 2 for raw data). This combination of analyses can better predict the diet of a fossil sample than just a single variable because they encompass different parts of the chewing cycle (Janis, 1990; Danowitz et al., 2016).Mesowear univariate datawas transformed from those of Fortelius and Solounias (2000), mesowear III data were taken fromDanowitz et al. (2016), and for theMexican data, an average per samplewas employed.Originally, the combination of extended mesowear and mesowear III (Danowitz et al., 2016) employed the 0−6 univariate mesowear scale developed by Mihlbachler et al. (2011). This scale was developed for Equoidea, but because horses have unique traits in their wear patterns, and given that the 0−3 univariate mesowear scale (Rivals et al., 2007a) was developed for its use in bison, and encompassesmost of the possible cusp relief and shape combinations described in nature, we employed the 0−3 scale, transforming the dataset of Danowitz et al. (2016) to this scale. The selected discriminant methodwas linear and common covariance, because our extended mesowear and mesowear III data came from the same order of magnitude (i.e., scales) andwere in covariance (i.e., the same teeth were scored both in the lingual and labial part of the ectoloph). Dietary category (browser, grazer, or mixed feeder) was the grouping variable (Danowitz et al., 2016). Finally, to test statistic differences among the multivariate centroids of the dietary categories, we performed a Wilks’ lambda test (α=0.05). The cluster analysis was performed with Statistica 10 software
1133
(Statsoft, 2011), whereas the discriminant analysis, chi-square, and Wilks’ lambda tests were carried out with JMP 8.0 (SAS Institute, Inc.,
https://www.jmp.com).
Repositories and institutional abbreviations.—The fossil specimens from La Piedad-Santa Ana and La Cinta-Portalitos are housed at the Colección del Laboratorio de Paleontología, Uni- versidad Michoacana de San Nicolás de Hidalgo (UM, CPOEI, PMB) located at the Faculty of Biology in Morelia, Michoacán, Mexico. Specimens from Viko Vijin are housed at the Colección Científica del Laboratorio de Paleobiología, campus Puerto Escondido, Universidad delMar (UMPE), Oaxaca,Mexico.
Results
The analyses showed that the mesowear patterns in the Mexican samples of Bison antiquus were similar to those of nonstrict grazers and mixed feeders. A summary of these mesowear pat- terns is shown in Table 1 (see Supplemental dataset 1 for raw mesowear values). Extended mesowear signatures in both La Cinta-Portalitos and La Piedad-Santa Ana showed a majority of low cusps (66.6% and 54.5 %, respectively), whereas the opposite was found in Viko Vijin, where the total sample dis- played high cusps. Rounded cusps were predominant among the samples. On the other hand, mesowear III signatures showed a large proportion of abrasiveness, with indices>2.8, and in some cases, the maximum wear index was reached (see Viko Vijin’s j-junction score, Table 1). The cluster analysis (Fig. 4.1) grouped the three Mexican
samples within the nonstrict grazers. Samples from La Cinta- Portalitos and La Piedad-Santa Ana formed one cluster close to the one of Connochaetes taurinus (Burchell, 1824) and Alce- laphus buselaphus (Pallas, 1766). Meanwhile, the Viko Vijin sample formed a cluster with Kobus ellipsiprymnus (Ogilby, 1833). The univariate mesowear analysis (Fig. 4.2) showed the highest values for La Cinta-Portalitos sample (1.66), followed by La Piedad-Santa Ana sample (1.54), and ending with the Viko Vijin sample (0.93). There were no statistically significant differences between
the mesowear univariate scores (0 −3) of La Cinta-Portalitos and La Piedad-Santa Ana with the grazer guild (p=0.32, 0.1, respectively), but there were statistically significant differences with the mixed feeder (p=0.0002, 0.0003, respectively) and browser guilds (p<0.0001, in both cases). On the other hand, the Viko Vijin scores showed no statistically significant differ- ences with the mixed feeder guild (p=0.29), but statistically significant differences with the grazer (p<0.0001) and browser (p=0.005) guilds.
Table 1. Summary of mean mesowear patterns of the fossil Bison antiquus of this study. %high=percentage of high cusps; %low=percentage of low cusps; %sharp=percentage of sharp cusps; %round=percentage of rounded cusps; mesial=mesial enamel band score; distal=distal enamel band score; j-junction=score of the intersection of mesial and distal enamel bands.
% Fossil sample
La Piedad-Santa Ana
Viko Vijin high % low % sharp %
La Cinta Portalitos 33.3 66.6 0 100 45.5 54.5 0 100
round mesial distal 3.8 3.7
3.9 3.7 j-
junction 3.3
3.7 100 0 6.2 93.75 2.8 2.8 4
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