The vertebral column of Chaetophractus villosus (Desmarest, 1804) (Chlamyphoridae, Cingulata, Xenarthra): anatomy and Thoracolumbar variation. Spinal cord relation




Armadillos, Vertebral morphology, Thoracolumbar number


Mammals of the Xenarthra clade show a large number of unusual characters in the skeleton, mainly in the vertebral column. In spite of the importance of the knowledge on the axial skeleton in this group, there are no detailed studies on the morphology of the entire vertebral column. Here we performed a comprehensive study of the vertebral column of Chaetophractus villosus (Desmarest, 1804), a representative of Chlamyphoridae, in order to provide a more reliable comparative framework among armadillos. Morphological description was based on 44 adult postcranial axial skeletons. As a complement to the morphological descriptions of the skeleton we studied the paths followed by blood vessels and nerves in close relationship to the axial skeleton (using 13 fresh adult specimens, six females and seven males, part of the doctoral Thesis of one of the authors). Intraspecific variability in the thoracolumbar number in C. villosus was also evaluated. We identified certain variability in the position of the first vertebral pair that bears a xenarthral facet, ranging from T4-T5 to T6-T7, being T5-T6 and T6-T7 the most frequent positions. The second pair of xenarthrales is set near the thoracolumbar limit, and ranges between T9-T10 and T11-L1 (T10-T11 in most specimens). The variability in the total number of thoracolumbars in C. villosus falls within the range of most mammals and sets controversy about an important morphological feature that groups extant Xenarthra and Afrotheria into the southern placentals (Atlantogenata). In this regard, a more comprehensive study of this character is necessary to elucidate the patterns of distribution of this trait among xenarthrans.


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Aldana-Marcos, J.H. 1996. Estudio experimental sobre dos peculiares estructuras del Armadillo Chaetophractus villosus: El núcleo de Onuf y la glándula de Harder. Doctoral Thesis. Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina. 533 p.

Asher, R.J. & Lehmann, T. 2008. Dental eruption in afrotherian mammlas. BMC Evolutionary Biology, 6: 1-10.

Asher, R.J.; Bennett, N. & Lehmann, T. 2009. The new framework for understanding placental mammal evolution. BioEssays, 31: 853-864.

Asher, R.J.; Lin, K.H.; Kardjilov, N. & Hautier, L. 2011. Variability and constraint in the mammalian vertebral column. Journal of Evolutionary Biology, 24(5): 1080-1090.

Attias, N.; Miranda, F.R.; Sena, L.M.M.; Tomas, W.M. & Mourão, G.M. 2016. Yes, they can! Three-banded armadillos Tolypeutes sp. (Cingulata: Dasypodidae) dig their own burrows. Zoologia, 33(4):1-8, e20160035.

Billet, G.; Hautier, L.; de Muizon, C. & Valentin, X. 2011. Oldest cingulate skulls provide congruence between morphological and molecular scenarios of armadillo evolution. Proceedings of the Royal Society B, 278(1719): 2791-2797.

Buchholtz, E.A. & Stepien, C.C. 2009. Anatomical transformation in mammals: Developmental origin of aberrant cervical anatomy in tree sloths. Evolution and Development, 11(1): 69-79.

Buchholtz, E.A.; Booth, A.C. & Webbink, K.E. 2007. Vertebral anatomy in the Florida Manatee, Trichechus manatus latirostris: A developmental and evolutionary analysis. The Anatomical Record, 290(6): 624-637.

Ciancio, M.R.; Castro, M.C.; Galliari, F.C.; Carlini, A.A. & Asher, R.J. 2012. Evolutionary implications of dental eruption in Dasypus (Xenarthra). Journal of Mammalian Evolution, 19: 1-8.

Delsuc, F.; Gibb, G.C.; Kuch, M.; Billet, G.; Hautier, L.; Southon, J. & Poinar, H.N. 2016. The phylogenetic affinities of the extinct glyptodonts. Current Biology, 26(4): R155-R156.

Engelmann, G. 1985. The phylogeny of the Xenarthra. In: Montgomery, G.G. (Ed.). The ecology and evolution of armadillos, sloths, and vermilinguas. Washington, D.C., Smithsonian Institution Press. p. 51-64.

Flower, W.H. 1885. An introduction to the osteology of the mammalia. London, Macmillan and Co. 383p.

Galliari, F.C. & Carlini, A.A. 2015. Ontogenetic criteria to distinguish vertebral types on the debated Xenarthran Synsacrum. Journal of Morphology, 276: 494-502.

Galliari, F.C.; Carlini, A.A. & Sánchez-Villagra, M.R. 2010. Evolution of the axial skeleton in armadillos (Mammalia, Dasypodidae). Mammalian Biology, 75(4): 326-333.

Gaudin, T.J. 1999. The morphology of xenarthrous vertebrae (Mammalia: Xenarthra). Fieldiana: Geology, New Series, 41: 1-38.

Gaudin, T.J. 2004. Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society, 140(2): 255-305.

Gaudin, T.J. & Biewener, A.A. 1992. The functional morphology of xenarthrous vertebrae in the armadillo Dasypus novemcinctus (Mammalia, Xenarthra). Journal of Morphology, 214: 63-81.

Gaudin, T.J. & Wible, J.R. 2006. Chapter 6: The phylogeny of living and extinct armadillos (Mammalia, Xenarthra, Cingulata): a craniodental analysis. In: Carrano, M.T.; Gaudin, T.J.; Blob, R.W. & Wible, J.R. (Eds.). Amniote paleobiology: perspectives on the evolution of mammals, birds and reptiles. Chicago, University of Chicago Press, 153-198p.

Grassé, P.P. 1955. Traité de Zoologie: anatomie, systématique, biologie. mammifères. Paris, Masson et Cie.

Gray, H. 1977. Osteology – The skeleton. In: Pick, T.P. & Howden, R. (Eds.). Anatomy, descriptive and surgical. New York, Gramercy Books. p. 33-216.

Hautier, L.; Bennett, N.C.; Viljoen, H.; Howard, L.; Milinkovitch, M.C.; Tzika, A.C.; Goswami, A. & Asher, R.J. 2013. Patterns of ossification in southern versus northern placental mammals. Evolution, 67(7): 1994-2010.

Hildebrand, M. 1985. Digging of quadrupeds. In: Hildebrand, M.; Bramble, D.M.; Liem, K.F. & Wake, D.B. (Eds.). Functional vertebrate morphology. Cambridge, Belknap Press. p. 89-109.

Hoffstetter, R. 1958. Xenarthra. In: Piveteau, J. (Ed.). Traité de paleontologie: Mammifères. París, Masson. v. 6, p. 535-636.

Howell, A.B. 1930. Aquatic mammals: their adaptations to life in the water. Springfield, Charles C. Thomas, 341 pp.

Jenkins, F.A. 1970. Anatomy and function of expanded ribs in certain edentates and primates. Journal of Mammalogy, 51(2): 288-301.

Lessertisseur, J. & Saban, R. 1967. Squelette Axial. In: Grasse, P.P. (Ed.). Traité de Zoologie. Mammifères, teguments, squelette. Paris, Masson. v. 16, fasc. 1. p. 584-708.

Luaces, J.P.; Rossi, L.F.; Aldana-Marcos, H.J. & Merani, M.S. 2011. The rete mirabile of the tail, an effective site for sampling sterile blood from armadillos (Dasypodidae, Xenarthra). Italian Journal of Zoology, 78(1): 63-69.

McDonald, H.G. 2003. Xenarthran skeletal anatomy: primitive or derived? (Mammalia, Xenarthra). Senckenbergiana biologica, 83(1): 5-17.

Narita, Y. & Kuratani, S. 2005. Evolution of the vertebral formulae in mammals: A perspective on developmental constraints. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 304(2): 91-106.

Oliver, J.D.; Jones, K.E.; Hautier, L.; Loughry, W.J. & Pierce, S.E. 2016. Vertebral bending mechanics and xenarthrous morphology in the nine-banded armadillo (Dasypus novemcinctus). The Journal of Experimental Biology, 219(19): 2991-3002.

Owen, R. 1868. On the anatomy of vertebrates. V.3, mammals. London, Longmans, Green, and Co. 612p.

Prasad, A.B.; Allard, M.W.; NISC Comparative Sequencing Program & Green, E.D. 2008. Molecular Biology and Evolution, 25(9): 1795-1808.

Ray, C.E. 1958. Fusion of cervical vertebrae in the Erethizontidae and Dinomyidae. Breviora, 97:1-11.

Rose, K.D. & Emry, R.J. 1983. Extraordinary fossorial adaptations in the oligocene palaeanodonts Epoicotherium and Xenocranium (Mammalia). Journal of Morphology, 175(1): 33-56.

Rose, K.D.; Krishtalka, L. & Stucky, R.K. 1991. Revision of the Wind River faunas, early Eocene of central Wyoming. Part 11. Palaeanodonta (Mammalia). Annals of the Carnegie Museum, 60: 63-82.

Sánchez-Villagra, M.R.; Narita, Y. & Kuratani, S. 2007. Thoracolumbar vertebral number: the first skeletal synapomorphy for afrotherian mammals. Systematic Biodiversity, 5: 1-7.

Scott, W. 1903-1905. Volume V: Mammalia of the Santa Cruz Beds: I. Edentata. In: Hatcher, J.B. (Ed.). Reports of the Princeton University Expeditions to Patagonia, 1896-1899. New Jersey, The University of Princeton. 364 p., 63 figs.






Original Article

How to Cite

Galliari, F. C., Rossi, L. F., & Aldana-Marcos, H. J. (2022). The vertebral column of Chaetophractus villosus (Desmarest, 1804) (Chlamyphoridae, Cingulata, Xenarthra): anatomy and Thoracolumbar variation. Spinal cord relation. Papéis Avulsos De Zoologia, 62, e202262032.