ENAMEL IN DASYPUS (XENARTHRA, CINGULATA): PHYLOGENETIC RELEVANCE

CASTRO, MARIELA C.; CIANCIO, MARTÍN R.; VIEYTES, EMMA C.; CARLINI, ALFREDO A.

Mendoza

Congreso; 4th INTERNATIONALPALAEONTOLOGICALCONGRESS; 2014

Reduction and simplification characterize dentition of Xenarthra, which is usually homodont,hipselodont, and lacks enamel. The presence of this latter was only mentioned for some Dasypodidae armadillos. In Euphractinae, it is exclusively known in Utaetus buccatus (late Eocene,Argentina). Among the Dasypodinae, the presence of enamel was mentioned for an Astegotheriini(Astegotherium; middle Eocene, Argentina) and was described as radial, bearing small prisms andabundant interprismatic matrix. In Dasypus, the occurrence of enamel is recognized in embryosof D. novemcinctus (late Pleistocene?present, America) and in subadults/adults of that species andD. hybridus. The present contribution comparatively describes the enamel microstructure in otherDasypus species. Deciduous and permanent molariforms of the extinct D. punctatus (late Pleistocene?early Holocene, Brazil) and the extant D. sabanicola were examined. The upper portion of their teeth was polished along the transversal and longitudinal axes, briefly treated with hydrochloric acid, and analyzed under Scanning Electron Microscope. As in the previously studied species, a vitreous layer is macroscopically observed in the apex of unworn deciduous molariforms. Under greater magnification, we observed that this tissue is amorphous and only growth lines are distinguished; it is interpreted herein as a thin cap of vestigial enamel deposited over the dentine. In fully formed permanent molariforms previous to its eruption, a continuous cap of enamel was detected around the entire tooth, ranging from 20 to 36 µm in thickness, with enamel tubules and growth lines parallel to the external surface of the tooth. No prisms were observed in D. hybridus, D. sabanicola, and D. punctatus. On the other hand, in D. novemcinctus the enamel has few scattered prisms, 3 to 4 µm in diameter, parallel to each other, either with open or closed sheath. Considering the enamel structure in the above-mentioned Astegotheriini, the ancestral condition of this tissue in Xenarthra could have been more complex, as in other placentals, and suffered a progressive reduction in the lineage of Dasypus. The retention of a thin enamel layer in the genus, in addition to the fact that it is the only living xenarthran with two functional dental generations, agrees with the basal phylogenetic position of Dasypus among the cingulates, as supported by cladistic analyses based both in morphologic and molecular data.