Enamel in dasypus (xenarthra, cingulata): phylogenetic interpretations relevance.

CASTRO, MC; CIANCIO MR; VIEYTES, E; CARLINI A.A:

Mendoza

Congreso; 4º International Plaeontological Congress,; 2014

IADIZA

Reduction and simplification characterize dentition of Xenarthra, which is usually homodont,hipselodont, and lacks enamel. The presence of this latter was only mentioned for someDasypodidae 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 teethwas 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 vitreouslayer is macroscopically observed in the apex of unworn deciduous molariforms. Under greatermagnification, 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 formedpermanent molariforms previous to its eruption, a continuous cap of enamel was detected aroundthe entire tooth, ranging from 20 to 36 μm in thickness, with enamel tubules and growth linesparallel 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 4μm in diameter, parallel to each other, either with open or closed sheath. Considering the enamelstructure in the above-mentioned Astegotheriini, the ancestral condition of this tissue in Xenarthracould have been more complex, as in other placentals, and suffered a progressive reduction inthe lineage of Dasypus. The retention of a thin enamel layer in the genus, in addition to the factthat it is the only living xenarthran with two functional dental generations, agrees with the basalphylogenetic position of Dasypus among the cingulates, as supported by cladistic analyses basedboth in morphologic and molecular data.