Dasypodidae—Armadillos // Glyptodontidae—Glyptodonts
A major group of South American origin has a history of name changes. Two names well entrenched in the literature for the group consisting of the armadillo-like animals plus the sloths are Order Edentata and Order Xenarthra. The Edentata was based on some members ("anteaters") having no teeth; other, toothed forms, have teeth without enamel; that is, consisting of dentine only. The name xenarthra refers to a unique extra articulation between the lumbar vertebrae (Fig. 1). Kurtén and Anderson (1980:128) characterize the edentates in general as not only having xenarthrous vertebrae, but also with "a varying number of cervical vertebrae (six to nine instead of the usual seven), ossified ribs that reach the sternum, an elongated sacrum, loss of enamel on the teeth, a small brain with a low level of organization, and low body temperature with poor thermoregulation."
Mammalian vertebrae join by the centra (the more or less cylindrical ventral portion) plus, except for the xenarthrans, by only anterior and posterior zygapophyses (prezygapophysis and postzygapophysis) coming off of the neural arch. The Cingulata and the Pilosa (sloths and myrmecophagid anteaters) are still grouped together at a higher rank (Magnorder Xenarthra).
Fig. 1. Anteater (Tamandua tetradactyla) vertebrae showing the extra articulation seen in xenarthrans. A = articular surface for the postzygapophysis; B = articulation surfaces for xenarthrous process. Anterior view on left, posterior on right. The strange look of the centrum is due to the loss of the epiphysis in this young individual.
Pleistocene regional cingulates belong to two families, the armadillos and the glyptodonts. These do not show up in North America until after the formation of the Central American land bridge in the Pliocene.
Literature. Kurtén and Anderson 1980.
Last Update: 21 Nov 2008