Supercontracting Muscle Properties Among Hyoid Musculature in Chameleons

Scientists have uncovered a second supercontracting muscle responsible for chameleons' extraordinary tongue projection. Previously, only the hyoglossus muscle was known to have this ability, but the study identified the sternohyoid superficialis muscle as another key player.

Researchers examined 15 Veiled chameleons (Chamaeleo calyptratus), measuring muscle contraction and structure. They found that supercontracting muscles can shorten beyond half their resting length due to perforated Z-discs in the muscle's sarcomeres. Interestingly, the sternohyoid profundus muscle lacked perforated Z-discs but still showed a similar tension profile, likely compensated by a broad attachment to the hyoid bone.

Immunohistochemical analysis confirmed that these two supercontracting muscles develop from separate origins, creating a unique muscular unit that extends to the sternum—a mechanism never observed in other vertebrates. This discovery deepens our understanding of chameleon biomechanics and their specialized tongue-shooting adaptations. 

Schneider NG, Henchal NA, Diaz Jr RE, Anderson CV. 2025 Feats of supercontractile strength: functional convergence of supercontracting muscle properties among hyoid musculature in chameleons. Proc. R. Soc. B 292: 20250078. https://doi.org/10.1098/rspb.2025.0078