Dental development in the tropical gar (Atractosteus tropicus) and the evolution of vertebrate dentitions

Dentitions have diversified enormously during vertebrate evolution, involving reductions, modifications, or allocations to prey seizing and processing regions. A combination of ancient and novel features related to dental and oropharyngeal apparatuses is found in extant lineages of non-teleost fishes, such as the gars. While relevant to evolutionary-developmental studies, gars have largely been overlooked regarding how their dentition arises, thus leaving our comprehension of the evolutionary history of vertebrate dentitions incomplete.

Here, we complement this knowledge gap by studying dental development in the tropical gar, Atractosteus tropicus. We follow ontogenetic changes from the initiation, tooth germ addition to the establishment of the larval replacing dentition. We pay attention to the progressive appearance of tooth fields, the emergence of dental patterns, the development of folded dentin morphology, and features related to tooth resorption and replacement. Furthermore, we identify snout elongation as the critical period when the general dentition layout becomes established.

Our study depicts the gar oropharyngeal apparatus as a system that is established based on patterned initiation, differential growth, replacement, and complex shaping of teeth. These features form a reference standpoint for the likely developmental processes employed in dentitions of fossil stem and crown bony vertebrates, including ray-finned fishes and tetrapods.