The evolution of specialized dentition in the deep-sea lanternfishes (Myctophiformes).

The evolution of heterodonty, the possession of varied tooth morphologies on the jaws of animals, has been relatively unexplored in ray-finned fishes compared to terrestrial vertebrates, and to an even lesser degree in deep-sea fish lineages. Lanternfishes (Myctophiformes) are an abundant and species-rich group endemic to deep-sea pelagic habitats. In this study, we document the presence of heterodonty on the oral jaws of lanternfishes, identifying differing anatomical and positional variations of dentition. We survey the anatomical variation in tooth morphology on the oral jaws of 114 lanternfish species across 37 genera and integrate our findings with a hypothesis of evolutionary relationships of lanternfishes to infer the number of times heterodonty evolved in this lineage. Our results indicate that heterodonty evolved at least six separate times on the oral jaws of lanternfishes, occurring as variable tooth morphologies in combination with villiform teeth. These combinations of tooth types include villiform plus hooked teeth, villiform plus hooked and recurved teeth, villiform plus spade, tricuspid, and hooked teeth, and villiform plus caniniform teeth. The reoccurring evolution of hooked teeth on the premaxilla and dentary in lanternfishes suggests heterodonty may serve an important functional role in their pelagic deep-sea environment. Hooked teeth could aid in securing and retaining prey in the oral cavity and allow for species to specialize on differing food resources, vital attributes for organisms living in open-ocean habitats.