“…Acipenser baerii and A. gueldenstaedtii are reared and raised in hatcheries in Europe for caviar and food production (Bronzi, Rosenthal, Arlati, & Williot, ; Williot et al, ). This has augmented interest in several aspects of their natural history, not only related to hatchery and rearing questions (Gisbert & Ruban, ; Psenicka et al, ; Zelazowska, ) but also regarding their development (Gisbert, ; Rodríguez & Gisbert, ; Song & Song, ), including staging tables and descriptions of embryonic and larval stages (Leprévost, Azaïs, Trichet & Sire, ; Ginsburg & Dettlaff, ; Park, Lee Sang, Kim, & Kwon, ; Schmalhausen, ). As a contribution to the study of the vertebrate skull and to provide information that will help to solve the evolutionary relationships among the species, we document the skeletal development of the skull and the pectoral girdle of A. baerii and A. gueldenstaedtii , and provide an overview of the developmental timing of the differentiation of skeletal elements.…”