TOKITA, M; Kyoto Univ.: Morphogenesis of unique jaw muscles in parrots

Parrots have developed novel head structures in their evolutionary history. The appearance of two new muscles for strong jaw adduction is especially fascinating in developmental and evolutionary contexts. However, the jaw muscle development of parrots has not been described, despite its uniqueness. To better understand evolution of unique jaw muscles of parrots, the peculiar skeletal myogenesis in the first visceral arch of cockatiel (Nymphicus hollandicus) was described, mainly focusing on the development of two new jaw muscles. One of the parrot-specific muscles, M. ethmomandibularis, was initially detected at Nymphicus stage 28 (N28) as the rostral budding of M. pterygoideus. After N32, the muscle significantly elongates rostrodorsally toward the interorbital septum, following a course lateral to the palatine bone. Another parrot-specific muscle, M. pseudomasseter, was first recognized at N36. The muscle branches off from the posteromedial M. adductor mandibulae externus and grows in a dorsolateral direction, almost covering the lateral surface of the jugal bar. In addition, unique patterning of the cephalic neural crest cell migration and the trigeminal nerve branches in parrot embryos was described with immunostaining.