New ontogenetic evidence on the septomaxilla ofTamandua andCholoepus (Mammalia, Xenarthra), with a reevaluation of the homology of the mammalian septomaxilla

• DOI: 10.1007/bf01027598
• Publication Date: 2005-01-20T11:42:38Z
• Authors: U. Zeller; J. R. Wible; M. Elsner
• Keywords: Xenarthra; Intramembranous ossification; Evolution of mammals

An intramembranous ossification at the anterior end of the cartilaginous nasal capsule is described for the first time in prenatal specimens of the anteaterTamandua and the slothCholoepus and redescribed in prenatal specimens of the armadillosDasypus andZaedyus. From comparisons of this bone with the septomaxilla of monotremes and various Mesozoic mammals, it is concluded that (1) the bone inTamandua andCholoepus is homologous with the central part (processus ascendens) of the bone inDasypus, Zaedyus, and other armadillos and (2) the xenarthran processus ascendens, in turn, is homologous with the central part of the septomaxilla of monotremes and various Mesozoic mammals. Therefore, the bone in question in xenarthrans is a true septomaxilla. It is further concluded that the armadillo septomaxilla has two neomorphic components: a lamina palatina beneath the cartilaginous nasal floor and a processus intrafenestralis extending rostrally into the nasal fossa.