Developmental dynamics of catshark cranial neural crest cells provide insights into gnathostome facial evolution.

Cranial neural crest cells (CNCCs) are a vertebrate-specific, multipotent cell population central to facial morphogenesis and a cellular substrate for evolutionary change. Although core CNCC developmental programmes are deeply conserved, changes in their gene expression programmes and cell behaviour underlie both macroevolutionary transitions and microevolutionary adaptations. While CNCC biology has been well characterized in bony vertebrates, comparatively little is known about CNCC properties and the behaviour of their derivatives in cartilaginous fishes (Chondrichthyes). To address this gap, we investigate CNCC development in a representative chondrichthyan: the small-spotted catshark (Scyliorhinus canicula). By integrating high-resolution molecular and morphological analyses, we reveal how conserved developmental programmes are modulated in chondrichthyans to generate divergent facial morphologies. We show that the molecular toolkit of CNCC is largely conserved across jawed vertebrates, and the developmental divergence and lineage-specific differences arise from divergent behaviour of their ectomesenchymal derivatives. These findings establish a high-resolution reference of CNCC biology in Chondrichthyes and uncover the evolutionary origins of both shared and lineage-specific traits, offering key insights into the developmental and evolutionary processes shaping gnathostome facial diversity.