Comparative multivariate analysis of 3-D reconstructed encephalon in extant and fossil Folivora (Pilosa) and other representative Xenarthra

ABSTRACT

The Magnorder Xenarthra includes recent and fossil forms of Cingulata, Vermilingua, and Folivora. Folivora consist of extant and extinct sloths, presenting a great diversification in terms of size and habits. To analyse endocranial morphological variation in sloths, we measured digital endocrania of representatives of both fossil and extant Xenarthrans, and compiled measurements from the literature for a variety of mammals representing different orders, sizes, and habits. A Principal Component Analysis combining both datasets revealed a conservative covariance structure among mammalian orders, with the arrangement of scores along the first principal component summarising nearly 93% of morphometric variation, related in an almost isometric trend. A second analysis held only for endocranial measurements from Xenarthran endocrania, produced second and third principal components scores showing a variation trend among sloths related to relative dimensions of the olfactory bulb and the hypophysis. Interpolation of these scores also revealed an overlapping between Folivora and Vermilingua representatives and the separation of Cingulata, related to the dimensions of the olfactory bulbs. These results suggest that the endocranial structures exhibit a conservative pattern, varying according to the overall size of the encephalon, but also point to some convergence related to fossorial and arboreal habitat uses.

KEYWORDS:

• Xenarthra
• Folivora
• multivariate analysis
• paleoneurology
• PCA

Acknowledgments

A previous version of this study was presented by R.V.A. as a MSc thesis to the Graduate Program in Biodiversity and Evolutionary Biology (PPGBBE) at Universidade Federal do Rio de Janeiro. The authors thank committee members I.S. Carvalho, L.S. Avilla and L. M. Pessôa for suggestions and corrections that greatly improved the original manuscript. We also thank D. Henriques (MN/UFRJ), M. Weksler (MN/UFRJ) S. M. Vaz (MN/UFRJ), for granting access to the specimens used in this research and for U. G. Cabral (MN/UFRJ) for sharing her thesis data. R. Costa (DNPM) and D. Bustamente kindly allowed access to the specimens of their own research. To “Centro de Diagnóstico por Imagem” (CDPI) through I. R. Kuroki and I. C. Kuroki, by conducting part of CT Scan exams. To Pedro Ernesto Hospital (HUPE) of Universidade do Estado do Rio de Janeiro (UERJ) through R. Mogami for the partnership in the realization of most of the CT scan exams, as well as the staff for the aid during CT scan exams. We also thank, R. T. Lopes and technician A. Machado, from “Laboratório de Instrumentação Nuclear, COPPE/UFRJ,” as well as M. H. P. Maurício and H. Alves from Image and Digital Microscopy Analysis group of the Chemical and Materials Engineering Department of Pontifícia Universidade Católica do Rio de Janeiro (DEQM/PUC-Rio), for the partnership in conducting the exams in the microtomography. To J. R. L. dos Santos (Instituto Nacional de Tecnologia/Ministério da Ciência e Tecnologia - INT/MCT) and Núcleo de Experimentação Tridimensional da Pontifícia Universidade Católica do Rio de Janeiro- NEXT/PUC-Rio), for the partnership that allowed the use of Materialise Mimics 10.01 software, without which this research could not be accomplished. To S. A. K. de Azevedo, for the partnership with “Laboratório de Imagem Digital” (LAPID – Museu Nacional) which permited the use of the laboratory for this research. We are also grateful to two anonymous referees for the comments and corrections that greatly improved the original manuscript. This study was partially supported by a graduate fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) to R.V.A and by a research fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) to J.A.O.

Authors’ contributions

RVA - Conceptualization, design, digital reconstructions, data assembly, multivariate analysis, synthesis, and paper writing; JAO - Conceptualization; data review; multivariate analysis, synthesis and paper writing; LC - Conceptualization, design, digital reconstructions, data review, paper writing.

Disclosure statement

The authors declare no competing interests.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior [Scholarship].