Carved teeth and strange jaws: How glyptodonts masticated

In this paper, the highly peculiar masticatory apparatus of glyptodonts is studied. The general morphology of the skull is analysed using a morphometr ic procedure, the Resistant Fit Theta Rho Analysis, which allows comparison among different biological forms. Here, a large terminal form, the late Pl eistocene genus Glyptodon. is compared with the smaller primitive Miocene g enus Propalaehoplophorus and with the generalised Recent armadillo Chaetoph ractus. The masticatory musculature of glyptodonts is reconstructed. Their tooth form and wear facets, as well as their mandibular symphysis and jaw j oint. are analysed. A model of jaw movement is constructed based on these a nalyses. It is demonstrated that the masticatory apparatus of glyptodonts h ad undergone a telescoping process, which was already underway in the most ancient forms whose skull is known. This process created problems in regard to the way stresses produced by mastication were absorbed by the mandible, and therefore it might be regarded as non-adaptive. Some functional explan atory hypotheses are discussed, such as a requirement of keeping the moment of the weight of the cranium small enough to be counterbalanced by the nec k muscles, or fitting the head into the armour.