Morphology and function of the hyoid apparatus of fossil xenarthrans (mammalia)

Abstract

The analysis of the hyoid apparatus of fossil xenarthrans provides insight on the form of the tongue and its function in food intake and intraoral processing. The hyoid apparatus of xenarthrans is notable for fusion among its elements. The presence of a V-bone, a complex consisting of fused basihyal and thyrohyal bones, is a consistent and probably synapomorphic feature of xenarthrans. Fusion of other elements is variable in fossil xenarthrans. Most fossil sloths retain independent elements, as in living dasypodids and mammals generally. Among nothrotheriids, the elements are slender and their articular surfaces indicate considerable mobility, and the relatively long and horizontal orientation of the geniohyoid muscle suggests considerable tongue protrusion. Among mylodontines, such as Paramylodon and Glossotherium, the elements indicate relatively mobile articulations, except between the stylo- and epihyals. The relatively posterior placement of the apparatus and the length and alignment of the geniohyoid muscle indicate considerable capacity for tongue protrusion. Scelidotherium, however, had rigidly articulated stylohyal and epihyal, and the apparatus lies farther anteriorly, which together with the elongated, steeply inclined mandibular symphysis, indicates a relatively shorter geniohyoid muscle and thus more limited capacity for tongue protrusion. A similar situation is indicated for Megatherium, casting doubt on the classical reconstruction of this sloth as having a long prehensile tongue. Among cingulates Prozaedyus resembles living dasypodids, indicating considerable tongue protrusion important in food acquisition and intake. More extensive fusion of hyoid elements occurs in the cingulates Glyptodon and Proeutatus, in which the stylohyal and epihyal at least, are fused into a single element termed the sigmohyal. The presence of this element supports recent proposals of a sister-group relationship between glyptodonts and eutatines. The rigidity of the apparatus suggests limited tongue protrusion, but the tongue, in glyptodonts at least, was a powerful structure important for intraoral manipulation of food.

Perspectivas arqueológicas para Patagonia Septentrional: Sitio Cueva Huenul 1 (Provincia del Neuquén, Argentina)

“…7A,C) y tiene forma de "U" en vista dorsal, similar a Glossotherium y Paramylodon (Pérez et al 2010). En Scelidotherium, el hueso tiene forma de "V" (Fig.…”

“…Dicha condición se ha mencionado para los Xenarthra y, entre éstos, el de CH1 se asemeja a los Pilosa en los que no hay un proceso lingual (Pérez et al 2010). El tamaño del ejemplar de CH1 resulta similar a algunos especímenes asignados a Scelidotherium (Pérez et al 2010), sin embargo, la mayoría de los basi-tirohiales de los perezosos descriptos del Cuaternario son de talla algo mayor.El basi-tirohial de CH1 es parabólico (el ancho es mayor que la longitud; Fig. 7A,C) y tiene forma de "U" en vista dorsal, similar a Glossotherium y Paramylodon (Pérez et al 2010).…”

“…El tamaño del ejemplar de CH1 resulta similar a algunos especímenes asignados a Scelidotherium (Pérez et al 2010), sin embargo, la mayoría de los basi-tirohiales de los perezosos descriptos del Cuaternario son de talla algo mayor.…”

“…Esta es pequeña, oval y con el eje mayor orientado horizontalmente. En los milodóntidos conocidos, las facetas del ceratohial están mejor definidas que en CH1; aunque tanto CH1 como los otros milodóntidos difieren claramente de Megatherium por presentar este último facetas prominentes y proyecciones anteriores del hueso (Pérez et al 2010). Las astas mayores están levemente comprimidas lateralmente.…”

Anatomy description of cervical region and hyoid apparatus in living giant anteaters Myrmecophaga tridactyla Linnaeus, 1758

“…In his description of giant anteaters, Naples (1999) states that these animals have a feeding system adapted to their peculiar cranial anatomy, with a long slender tongue that can be projected to a distance greater than the length of the skull to rapidly capture and transfer food to its oral cavity, which is supported by a large, elongated hyoid apparatus. The functions of the hyoid apparatus are to control the airways and to support and maintain the position of the tongue during feeding; it also participates indirectly in the production of sounds (Pérez et al 2010). Pérez et al (2010) formulated hypotheses about the bony elements of the hyoid apparatus in various fossil species of the superorder Xenarthra, seeking answers about the mechanism of tongue movement and the food intake pattern.…”