The Glyptodontidae (Mammalia, Xenarthra) are one of the most common paleofaunistic elements in the South American megafauna. In this context, of the six genera most frequently recorded in the South American Pleistocene (Glyptodon, Neosclerocalyptus, Hoplophorus, Neuryurus, Panochthus and Doedicurus), at least four (Hoplophorus, Neuryurus, Panochthus and Doedicurus) present structures in their caudal armor that could have had defensive/offensive functions, in addition to a solid dorsal carapace and cephalic shield. In this article, we provide the first record and description of a series of highly modified osteoderms, located at the anterolateral region and over the cephalic notch of the dorsal carapace. These "spine"-like osteoderms were found in two of the largest Pleistocene glyptodonts: Glyptodon munizi (early-middle Pleistocene) and, G. reticulatus (late Pleistocene-early Holocene). We propose that they are structures for protection of the neck and abdomen, the most vulnerable body regions of these large armored animals, since they are not covered by the cephalic shield, carapace or caudal armor. Noteworthy, structures like those described herein are not known in glyptodonts recorded before the Great American Biotic Interchange (GABI), so it could be a reaction to the arrival of Smilodon and Arctotherium (Carnivora, Mammalia) the largest terrestrial carnivores that ever lived in South America.Facultad de Ciencias Naturales y Muse
