Accessory protection structures in Glyptodon Owen (Xenarthra, Cingulata, Glyptodontidae)

Abstract

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 * Corresponding author. RésuméLes Glyptodontidae (Mammalia, Xenarthra) sont l'un des éléments paléofaunistiques les plus communs de la mégafaune en Amérique du Sud. Dans ce contexte, des six genres le plus souvent enregistrés dans le Pléistocène (Glyptodon, Neosclerocalyptus, Hoplophorus, Neuryurus, Panochthus et Doedicurus), au moins quatre (Hoplophorus, Neuryurus, Panochthus et Doedicurus) présentent dans leur armure caudale des structures qui auraient pu avoir des fonctions défensives/offensives, en plus d'une carapace dorsale solide et un bouclier céphalique. Dans cet article, nous proposons le premier enregistrement et la description d'une série d'ostéodermes très modifiés, situés dans la région antérolatérale et au-dessus de l'encoche céphalique de la carapace dorsale. Ces structures se rencontrent chez deux espèces du genre Glyptodon, l'une des plus grandes formes de Glyptodontidae du Pléistocène, G. munizi (Pléistocène inférieur et moyen), et G. reticulatus (Pléis-tocène supérieur -Holocène inférieur). D'un point de vue morphologique, ces ostéodermes montrent une forme caractéristique en « épine ». Les ostéodermes décrits ici sont interprétés comme des structures de protection et de défense du cou et du ventre, régions les plus vulnérables de ces grands animaux à armure, car elles ne sont pas recouvertes par le bouclier céphalique, la carapace ou l'armure caudale. Enfin, il est intéressant de noter que ces types de structure ne sont pas enregistrés dans la paléofaune de Glyptodontidae qui vivaient avant le Great American Biotic Interchange (GABI), un processus migratoire qui marque l'arrivée de certains des plus grands prédateurs (Carnivora), ayant jamais vécu en Amérique du Sud (par exemple Smilodon, Arctotherium).

Ancient DNA from the extinct South American giant glyptodont Doedicurus sp. (Xenarthra: Glyptodontidae) reveals that glyptodonts evolved from Eocene armadillos

“…; Zurita et al . ). They were one of the most abundant, diverse and conspicuous elements of the isolated South American mammal fauna throughout much of the late Cenozoic (Rose ; Soibelzon et al .…”

Late Pliocene Glyptodontinae (Xenarthra, Cingulata, Glyptodontidae) of South and North America: Morphology and paleobiogeographical implications in the GABI

“…In sum, the shared characters between the northern South American and the southern North American taxa may be listed as follows: a) all the osteoderms present a great development of the central figure, which is much larger than the peripheral ones, representing a primitive condition seen in Boreostemma; in P. uquiensis and the basal species of Glyptodon (G. munizi) the central figures become larger toward the posterior, anterior and lateral regions of the dorsal carapace, while in the central area this central figure seems to be as large as the peripheral ones; b) the annular and radial sulci that delimit the central and peripheral figures are much narrower and shallower than in P. uquiensis and Glyptodon munizi; this particular morphology is preserved in derived species of Glyptotheriun (G. arizonae, G. cylindricum, G. mexicanum and G. floridanum) (see, among others, Osborn, 1903;Simpson, 1929;Gillette and Ray, 1981); on the contrary, in derived species of Glyptodon (e.g., Glyptodon reticulatus) the annular and radial sulcus become deeper and more pronounced (Duarte, 1997;Zurita et al, 2010); c) in P. uquiensis the preserved osteoderms seem to be smaller, but thicker than those of G. texanum. In fact, the relationship between the maximum diameter and the thickness of the osteoderms of the lateral-dorsal and dorsal regions of the carapace is approximately 4.4e5.4 in Boreostemma?…”

“…3(B)). c) One highly modified conical osteoderm corresponds to the ventro-lateral margin of the carapace, and represents a synapomorphy for the subfamily Glyptodontinae (see Ameghino, 1889;Duarte, 1997;Zurita et al, 2010). It measures 63 mm by 61 mm in diameter and 19 mm thick (Fig.…”

“…In addition, the ventral border of the carapace presents a row of highly modified conical osteoderms, which could have had defensive functions (see Zurita et al, 2010).…”

The GABI in Southern South America

“…Changes in behaviour of prey related with increasing predation risk may cause, i.e., modifications in diet, temporal changes in feeding patterns, spatial changes in habitat use, or changes in patch selection (Lima and Dill 1990). Zurita et al (2010) suggested that some glyptodonts developed a series of highly modified "spine"-like osteoderms (located at the anterolateral region and over the cephalic notch of the dorsal carapace) as a protection structures for the neck and abdomen. These are the most vulnerable body regions of these large armored animals, since they are not covered by the cephalic shield or carapace.…”