Ray-finned fishes (Actinopterygii) are the dominant vertebrate group today (+30 000 species, predominantly teleosts), with great morphological diversity, including their dentitions. How dental morphological variation evolved is best addressed by considering a range of taxa across actinopterygian phylogeny; here we examine the dentition of
Polyodon spathula
(American paddlefish), assigned to the basal group Acipenseriformes. Although teeth are present and functional in young individuals of
Polyodon
, they are completely absent in adults. Our current understanding of developmental genes operating in the dentition is primarily restricted to teleosts; we show that
shh
and
bmp4
, as highly conserved epithelial and mesenchymal genes for gnathostome tooth development, are similarly expressed at
Polyodon
tooth loci, thus extending this conserved developmental pattern within the Actinopterygii. These genes map spatio-temporal tooth initiation in
Polyodon
larvae and provide new data in both oral and pharyngeal tooth sites. Variation in cellular intensity of
shh
maps timing of tooth morphogenesis, revealing a second odontogenic wave as alternate sites within tooth rows, a dental pattern also present in more derived actinopterygians. Developmental timing for each tooth field in
Polyodon
follows a gradient, from rostral to caudal and ventral to dorsal, repeated during subsequent loss of teeth. The transitory
Polyodon
dentition is modified by cessation of tooth addition and loss. As such,
Polyodon
represents a basal actinopterygian model for the evolution of developmental novelty: initial conservation, followed by tooth loss, accommodating the adult trophic modification to filter-feeding.
Making teeth to order: conserved genes reveal an ancient molecular pattern in paddlefish (Actinopterygii)