Tooth reorientation affects tooth function during prey processing and tooth ontogeny in the lesser electric ray, Narcine brasiliensis.

The dental anatomy of elasmobranch fishes (sharks, rays and relatives) creates a functional system that is more dynamic than that of mammalian dentition. Continuous dental replacement (where new teeth are moved rostrally to replace older ones) and indirect fibrous attachment of the dentition to the jaw allow teeth to reorient relative to the jaw over both long- and short-term scales, respectively. In this study, we examine the processing behavior and dental anatomy of the lesser electric ray Narcine brasiliensis (Olfers, 1831) to illustrate that the freedom of movement of elasmobranch dentition allows a functional flexibility that can be important for complex prey processing behaviors. From static manipulations of dissected jaws and observations of feeding events in live animals, we show that the teeth rotate during jaw protrusion, resulting in a secondary grasping mechanism that likely serves to hold prey while the buccal cavity is flushed free of sediment. The function of teeth is not always readily apparent from morphology; in addition to short-term reorientation, the long-term dental reorientation during replacement allows a given tooth to serve multiple functions during tooth ontogeny. Unlike teeth inside the mouth, the cusps of external teeth (on the portion of the tooth pad that extends past the occlusal plane) lay flat, such that the labial faces act as a functional battering surface, protecting the jaws during prey excavation.

Batoid wing skeletal structure: novel morphologies, mechanical implications, and phylogenetic patterns.

The skeleton of the "wings" of skates and rays consists of a series of radially oriented cartilaginous fin rays emanating from a modified pectoral girdle. Each fin ray consists of small, laterally oriented skeletal elements, radials, traditionally represented as simple cylindrical building blocks. High-resolution radiography reveals the pattern of calcification in batoid wing elements, and their organization within the fin ray, to be considerably more complex and phylogenetically variable than previously thought. Calcification patterns of radials varied between families, as well as within individual pectoral fins. Oscillatory swimmers show structural interconnections between fin rays in central areas of the wing. Morphological variation was strongly predictive of locomotor strategy, which we attribute to oscillatory swimmers needing different areas of the wing stiffened than do undulatory swimmers. Contributions of various forms of calcification to radial stiffness were calculated theoretically. Results indicate that radials completely covered by mineralized tissue ("crustal calcification") were stiffer than those that were calcified in chain-like patterns ("catenated calcification"). Mapping this functionally important variation onto a phylogeny reveals a more complicated pattern than the literature suggests for the evolution of locomotor mode. Therefore, further investigation into the phylogenetic distribution of swimming mode is warranted.