Morphology, evolution and function of feeding in the giant anteater (Myrmecophaga tridactyla)

The edentulous giant anteater (Myrmecophaga tridactyla) ingests food using a slender, elongated sticky tongue which can project to a distance greater than the cranial length. A large and elongated hyoid apparatus, including a long stylohyal, epihyal, reduced ceratohyal and fused basihyal-thyrohyal f used to a partially ossified thyroid cartilage, supports the tongue. The fu sion pattern and relative hyoid element sizes in adult Myrmecophaga differ from those in other xenarthran anteaters, tree and ground sloths, and armad illos. The hyoid bones have synovial joints with articular surfaces permitt ing great freedom of movement. A unique hyoid muscle arrangement enables My rmecophaga to project the tongue with great speed and precise positional co ntrol. This muscle arrangement combined with an elongated secondary palate, accommodates the retracted tongue within the oropharynx without compromisi ng the animal's ability to breathe. Maximum gape is reached at a few degree s of mandibular depression, but the oral opening is increased to 2 cm by th e extreme length of the anterior facial region. Gape is further increased b y medial rotation and depression of the unfused mandibular rami at the ment al symphysis. This movement, even without mandibular depression, permits pr otraction and retraction of the elongated tongue. Mandibular rotation in li eu of depression and elevation simplifies jaw movements made by a smaller u niquely modified muscle mass over shorter distances, therefore increasing t he speed with which anteaters can ingest food, and complements the extremel y rapid tongue protrusion-retraction cycle.