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Epaxial Musculature in Armadillos, Sloths, and Opossums: Functional Significance and Implications for the Evolution of Back Muscles in the Xenarthra
Ist Teil von
Journal of mammalian evolution, 2018-12, Vol.25 (4), p.565-572
Ort / Verlag
New York: Springer US
Erscheinungsjahr
2018
Quelle
SpringerLink
Beschreibungen/Notizen
To investigate the evolution of xenarthran epaxial muscles, fresh specimens of the North American Common long-nosed armadillo
Dasypus novemcinctus
and of a marsupial, the Virginia opossum
Didelphis virginiana
, were dissected. Data from one fixed specimen of a two-toed sloth
Choloepus didactylus
were also used for comparison, because it is a xenarthran exhibiting a highly derived locomotor mode. The opossum was used to represent a more generalized mammalian condition. Each of the three mammalian epaxial muscle groups, the iliocostalis, longissimus dorsi, and transversospinalis, was removed and its mass was determined. All data were corrected for body mass and length. Unpaired, one-tailed t-tests showed the average mass of the iliocostalis and transversospinalis of
Dasypus
to be significantly larger than the mass of the same muscles in
Didelphis
, whereas the average mass of the longissimus dorsi was not statistically different between the two species. In agreement with pronounced lateral bending and de-emphasized dorso-ventral flexion and extension,
Choloepus
also had a relatively large iliocostalis and small longissimus. Our limited data suggest that this condition was inherited from non-arboreal and probably digging early xenarthrans. We believe the relatively larger iliocostalis and transversospinalis muscles in
Dasypus
can be attributed to the need to provide vertical stabilization of the trunk and resist lateral reaction forces generated by digging. Thus, for Xenarthra it represents a synapomorphy linked to adaptations for fossoriality.