Abstract
The morphological characteristics of the mandible of adult Chaetophractus vellerosus (Gray, 1865) and Zaedyus pichiy (Desmarest, 1804) were studied to establish its generalized design and to identify inter- and intra- (sexual) specific differences. Morphological descriptions were complemented with the application of univariate and multivariate (analysis of correlation matrices, PCA, discriminant analysis) techniques. The mandible of both species is very similar, and is characterized by elevated condyle, well developed angular process, distinct coronoid process, tooth row which extends to the rear end of the angle between body and ramus, and unfused but firm symphysis. Although both armadillos are omnivorous, a more slender configuration of the jaw in Z. pichiy could be indicative of a better adaptation of its masticatory apparatus to insectivory. The PCA showed an almost total segregation of both species on PC1 (47.7% of the total variance), with C. vellerosus being associated to mandibles taller and with wider body and ramus. Zaedyus pichiy was characterized by heavy loadings of length parameters on PC2 (22.6% of the variance). A small degree of sexual dimorphism was found, with size-based differences in C. vellerosus (larger mandibles in females) and shape-based differences in Z. pichiy (taller mandibles in males, longer ones in females). Correlations between variables were higher in males of both species, indicating a more stable shape of the mandible than in females. The selected parameters to discriminate sexes were the body length of the mandible in C. vellerosus (correct classification: ca. 86% in males, 81% in females), and the height of the mandible at the level of the last tooth in Z. pichiy (near 85% of right assignment in both sexes). The inclusion of a new variable (body length) in the latter species improved the classification of the females to 100%. Teeth are typically 10 in C. vellerosus and 9 in Z. pichiy, but aberrancies in this basic number, such as unilateral or bilateral extra or fewer teeth, are common.
Highlights
Measurements were performed with digital callipers (0.01 mm) over lineal projections on the graph paper (Fig. 1) to record four lengths and four heights: total length (TL); body length (BL); length of the dental series (LDS); ramus width (RW); total height (TH); condylar height (CH); and height at the level of the first tooth (HFT) and at the last tooth (HLT)
The number and exact position of these foramina can vary between individuals of each species, but they are generally four and locate between the level of the second and the fifth alveoli in the screaming hairy armadillo (Figs 2-5), and between the first and fourth alveoli in the pichi (Figs 6-9)
In particular, have different food preferences, ranging from herbivores to insectivores and carnivores, but they generally act as opportunistic omnivores that usually consume a wide variety of food items –insects and other invertebrates, plant material, small vertebrates, carrion, depending probably on the relative abundance thereof (Redford, 1985)
Summary
Caracterización morfológica y diferencias sexuales en la mandíbula de los armadillos Chaetophractus vellerosus y Zaedyus pichiy (Xenarthra: Dasypodidae), con consideración de aspectos dietarios. The screaming hairy armadillo Chaetophractus vellerosus (Gray, 1865) and the pichi Zaedyus pichiy (Desmarest, 1804) belong to the most widespread and diverse xenarthran group, the family Dasypodidae (Order Cingulata). Both species have a large distribution in South America, from where they are native, and are abundant in Argentina and Chile (Redford & Eisenberg, 1992; Wetzel et al, 2007), coexisting in some areas of their distributional range (Abba & Vizcaíno, 2011). Sidorkewicj & Casanave the dietary diversity of each species, it may be difficult to predict accurately behaviour or diet on the basis of morphology, even after comparison with other species with analogous morphological adaptations. Wible & Gaudin (2004) performed an exhaustive morphological characterization of the mandible of E. sexcinctus as part of a bone-by-bone description of the skull, and they made comparisons with other xenarthrans and nonxenarthrans taxa in order to place the cranial osteology of this species in a phylogenetic context. Squarcia et al (2006) performed a morphological description of the mandible of Chaetophractus villosus; subsequent work demonstrated the existence of sexual dimorphism in the mandible of this species, being females the larger sex (Squarcia et al, 2009)
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