Finite element and morphological analysis in extant mammals’ claws and quaternary sloths’ ungual phalanges

ABSTRACT

As the ungual phalanges of tetrapods are the first structures that interact with the substrate, studying them is of great importance when wanting to know the locomotor behaviour of different species. In this work, we analyse the ungual phalanges of the third finger from the manus of several Pleistocene sloths: G. robustum, L. armatus, M. jeffersonii, M. americanum, S. leptocephalum; and of a wide range of extant xenarthrans and other mammals. The third finger of the manus was chosen because of its larger size and nearly perfect bilateral symmetry, which enhances the possibility to observe functional differences between taxa. The analysis performed on them were of the inner and external curvature and the finite element method. By comparing the results obtained for the fossils and the extant species we were able to indicate possible habits for these Pleistocene ground sloths. Through these analyses the three mylodontid sloths: G. robustum, L. armatus and S. leptocephalum showed a preference for strenuous activities such as digging. On the contrary, M. jeffersonii and M. americanum, although they showed similar resistant structures, they learned more towards a less specific locomotor habit, such as generalised terrestrial mammals.

KEYWORDS:

• Biomechanics
• pleistocene
• xenarthra
• sloth
• finite elements
• ungual phalanx

Acknowledgments

We would like to thank Amanda Millhouse (National Museum of Natura History, Department of Paleobiology, Smithsonian Institution), Carla Suertegaray Fontana (Coleção de Mamíferos da Pontifícia Universidade Católica do Rio Grande do Sul), Marcelo Reguero (Museo de la Plata), Itatí Olivares (Museo de la Plata), Marcia Maria de Assis Jardim (Coleção de Mamíferos do Museu de Ciências Naturais da Fundação Zoobotânica), Andrés Rinderknecht (Museo Nacional de Historia Natural), Enrique González (Museo Nacional de Historia Natural), Sabrina Riverón and Ernesto Elgue (Colección de Vertebrados de la Facultad de Ciencias) and the workers at the Museo Paleontológico Armando Calcaterra for giving us access to the collections under their care. Also, we want to thank the Agencia Nacional de Investigadores (ANII) and National Geographic for the financial support given through a master’s scholarship.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary Material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Agencia Nacional de Investigación e Innovación [POS_NAC_2014_1_102270] and National Geographic, grant 178431.