The diversity of deep sea anglerfishes (suborder: Ceratioidei): describing trends in cranial and tooth morphologies

Deep sea anglerfishes (suborder: Ceratioidei) are an enigmatic clade of bathypelagic fishes known for their extreme sexual dimorphism, bioluminescent lures, and nightmarish appearance. Because ceratioids are difficult to observe in situ, little is known about their ecology. Food is scarce in the bathypelagic zone, yet deep sea anglers exhibit immense diversity in their trophic morphologies that suggest variable feeding modes. To shed light on our understanding of ceratioid trophic ecology and feeding strategies, we used micro-CT scans to measure functional feeding traits, such as tooth height, tooth spacing, and lower jaw shape for 20 species. Our primary goal was to use the ceratoid feeding morphology to generate hypotheses for how these creatures feed. With a hierarchical clustering analysis, we identified four distinct morphotypes that we coined "grabbers", "cagers", "hybrids", and "extreme cagers" based on the functional characteristics of the dentitions. For example, many "grabbers" have several stout, tightly packed teeth that enable the fish to grab prey with their jaws. By contrast, "cagers" possess a few long but narrow fangs that are poorly built for grabbing or puncturing. We posit "cagers" use their dentitions like a barrier to prevent prey captured via suction feeding from escaping. Furthermore, all large ceratioid fangs are depressible and can fold into the mouth but may not extend outward, thereby facilitating the unidirectional movement of large prey into the mouth and increasing prey retention.