Dental enamel structure in long-nosed armadillos (Xenarthra: Dasypus) and its evolutionary implications

CIANCIO, M.R.; VIEYTES, E. C.; CASTRO, MC; CARLINI A.A.

ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2020 vol. 2020 p. 1 - 16

0024-4082

Most xenarthrans have a reduced and simplified dentition that lacks enamel. However, the presenceof prismatic enamel has been recorded in the Eocene armadillos Utaetus buccatus (Euphractinae)and Astegotherium dichotomus (Astegotheriini). Among extant xenathrans, the occurrence of enamelhas been recognized only in the long-nosed armadillo, Dasypus novemcinctus (Dasypodinae), but itsmicrostructure has never been described. In this contribution, we analyze the enamel microstructurein deciduous and permanent teeth of four Dasypus species. In deciduous molariform teeth of somespecies, we identified an apical cap of vestigial enamel (without crystalline structure), interpreted asan amorphous ameloblastic secretion. In permanent teeth, a thin layer of true enamel is found in theapical portion of unworn molariforms. The enamel is prismatic in D. novemcinctus, but in D.hybridus, D. sabanicola, and D. punctatus it is prismless. Taking into account the Eocene species ofarmadillos, the ancestral condition of enamel in cingulates could have been more complex (as inother placentals) and undergone progressive reduction, as shown in the Dasypus lineage. In light ofprevious genetic and developmental studies, we review and briefly discuss the processes that canaccount for the enamel reduction/loss in extant and extinct armadillos. The retention of enamel, andthe fact that this genus is the only living xenarthran with two functional generations of teeth,supports the early divergence of Dasypus lineage among living cingulates, in agreement withmorphological and molecular analyses.