Hyoid apparatus of Panochthus sp. (xenarthra; Glyptodontidae) from the late pleistocene of the Pampean Region (Argentina). Comparativ description and muscle reconstruction

Abstract

The main function of the hyoid apparatus in mammals is to control the entry and exit of air in the body, provide support to the tongue, hold it in position and give it movement. In some species, it also participates in the modulation of sounds produced by vocal cords. Its preservation as fossil is exceptional and very little known. It allows proposing hypotheses about how the mentioned functions would be carried out. The finding and study of two new specimens assigned to the glyptodontid Panochthus sp., from Lujanian sediments (Late Pleistocene) of the Pampean Region, permitted: 1) to study the anatomy and propose a new organization of the hyoid apparatus in glyptodontids, 2) to describe in detail its elements (even the thyroid cartilage), 3) to compare it with materials already published of Glyptodon cf. G. clavipes, and 4) to analyze and compare the muscles' actions. In adult mammals, this apparatus is formed generally by ten bony elements, (1) stylohyals (paired), (2) epihyals (paired), (3) ceratohyals (paired), (4) thyrohyals (paired) and (5) basihyal (unpaired); and 2 paired cartilaginous elements, (a) tympanohyals and (b) chondrohyals. In glyptodonts, the elements (1), (2), (3) form the sigmohyals (paired), and (4) and (5) the V-bone (unpaired). The bony elements of Panochthus sp. are more gracile and long than those of Glyptodon cf. G. clavipes, and in the former, the musculature is more developed. The study of the new specimens suggests that Panochthus sp. could have more freedom of tongue movement than Glyptodon cf. G. clavipes, which possibly implied a different use of food resources.