A Comparative Analysis Of The Structure Of The Dentinoenamel Junction In Mammals.

Studies of the gross morphology and microstructure of teeth have provided a great deal of information about the function and evolution of mammals. Among the structural features studied, the dentinoenamel junction has received relatively little attention. In the present work, we used ground sections to perform a comparative analysis of the structure of the dentinoenamel junction (DEJ) among diverse mammalian species. Among the species studied, only two (human and Miguelsoria parayirunhor) presented a scalloped DEJ. In the other 14 species analyzed, the DEJ surface was formed by tiny spikes and depressions, corresponding to the impression of enamel prisms. Our results show that the topography of the DEJ in the analyzed taxa apparently does not relate to dietary, functional or structural features.43427728

Osteoderm histology of Late Pleistocene cingulates from the intertropical region of Brazil

During the Late Pleistocene, several possibly endemic cingulate species, known mostly from isolated osteoderms, carapace fragments, and caudal tubes, coexisted in the Brazilian Intertropical Region. Here, we describe the osteoderm microstructure of Pachyarmatherium brasiliense, as well as the glyptodonts Panochthus greslebini, Panochthus jaguaribensis and Glyptotherium sp., in order to provide additional species-diagnostic characters and shed light on their evolutionary relationships. Pachyarmatherium brasiliense lacks several derived features shared by glyptodonts and pampatheres, such as extensive bone remodeling, fibers arranged in large bundles, and relatively poorly developed layers of compact bone, thus supporting its exclusion from glyptodonts as suggested by a recent cladistic study. The osteoderm histology of P. greslebini resembles that of other species of Panochthus (e.g., Panochthus frenzelianus). By contrast, the presence of relatively thick layers of compact bone, the configuration and size of resorption areas, the absence of randomly oriented lateral fiber bundles, and the absence of an intermediary region between the compact and trabecular bone potentially support the exclusion of Panochthus jaguaribensis from the genus. Finally, osteoderms of the Brazilian specimens of Glyptodontinae share histological features with Glyptotherium floridanus, rather than Glyptodon, thus reinforcing their assignment to Glyptotherium. These results highlight the relevance of histological osteoderm characters in cingulate systematics, ands call for further and more comprehensive studies