The present study describes in detail for the first time the skeleto-muscular system of the jaw and hyoid apparatus (i.e. feeding apparatus) of seedsnipes (Thinocoridae), a small (two genera, four species) South-American bird family the biology and particularly the diet of which are still barely known. Morpho-functional analyses interpreted in the light of presently available behavioural and diet data show a strongly developed adaptation to the removal of attached plant items based on the acquisition of the separate control of jaws. In order to acquire this mechanism and because they are separated in two very different size-classes, large Attagis and small Thinocorus species did not modify the same osteo-muscular structures. Attagis species expanded m. pseudotemporalis superficialis of which they increased the intricacy of the internal aponeurotic system. Thinocorus species evolved a specific orbito-zygomatic process (mainly by expansion and fusion of postorbital and zygomatic processes by ossification of aponeuroses), expanded the medial portion of the external adductor of the mandible and increased the complexity of the aponeuroses of this medial portion. Seedsnipes appear to be well specialized in the continuous removal of small plant fragments thanks to a tongue raising mechanism joint to enlarged salivary glands and crenate areas in the buccal cavity. Thinocoridae seem to have followed a morpho-functional evolutionary pathway similar to that followed by sandgrouse (Pteroclididae) in the course of the adaptation of their bill and hyoid apparatus to a vegetarian diet essentially based on the removal of small attached plant fragments in rather similar habitat conditions.
Aves, Charadriiformes, Thinocoridae, Thinocorus, Attagis, functional morphology, feeding adaptations, jaw and hyoid apparatus, birds, seedsnipes, sandgrouse.