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Allometric and Group Differences in the Xenarthran Femur

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Abstract

The aim of this study is to analyze shape variation in the xenarthran femur to gain insights into their behavior and locomotion. Specimens of both Cingulata (armadillos and glyptodonts) and Pilosa (anteaters and sloths) were studied and within each group body mass varies by several orders of magnitude. The main focus of the analysis was allometric variation in femoral shape in the three groups studied, armadillos, glyptodonts, and pilosans. Three dimensional coordinates were recorded for 40 homologous landmarks on each of 51 xenarthran femurs. The data were analyzed by geometric morphometric methods, and form space analysis was used to identify the allometric variation in each of the three groups. Across all groups, larger specimens tended to have larger articular surfaces, more robust femora generally, and the shape of the femoral condyles was more suited to extended postures. In addition, in larger specimens the medial condyle was much larger than the lateral condyle and the third trochanter was located more distally. The larger armadillo femora had a greater trochanter located considerably proximal to the femoral head and this is thought to improve femoral extension, but in glyptodonts and pilosans the larger specimens had a greater trochanter that was far lateral to the femoral head and this is interpreted as enhancing femoral rotation.

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Acknowledgements

The authors acknowledge M. Reguero, L. Pomi, and I. Olivares (Museo de La Plata), A. Kramarz (Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires), and A. Tauber (Museo Regional Provincial Padre Molina) for access to collections. This is a contribution to the projects PIP-CONICET 1054, PICT 0143 and UNLP N 674.

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Authors and Affiliations

  1. School of Anatomy and Human Biology, University of Western Australia, Crawley, 6009, Australia

    Nick Milne

  2. División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina

    Nestor Toledo & Sergio F. Vizcaíno

  3. CONICET, Buenos Aires, Argentina

    Nestor Toledo & Sergio F. Vizcaíno

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  1. Nick Milne
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  2. Nestor Toledo
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  3. Sergio F. Vizcaíno
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Correspondence to Nick Milne.

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Table 2 Specimens included in the analysis
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Milne, N., Toledo, N. & Vizcaíno, S.F. Allometric and Group Differences in the Xenarthran Femur. J Mammal Evol 19, 199–208 (2012). https://doi.org/10.1007/s10914-011-9171-0

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