Meeting Abstract
Durophagy has evolved several times within the elasmobranchs. The stingray family Myliobatidae is composed almost entirely of durophagous taxa, except for the planktivorous manta and devil rays. These durophagous rays use rigid jaws, pavement-like dentition, and hypertrophied jaw muscles to crush and consume mollusks and crustaceans. The curvature of the upper and lower tooth plates vary considerably from one another, as well as between related taxa. We hypothesize that this difference in curvature will affects feeding performance and, therefore, patterns of ecological niche partitioning. For this study, we focused on the genera that represent the two morphological extremes: Aetomylaeus where a moderately curved top tooth plate occludes with a relatively flat lower tooth plate, and Rhinoptera which have highly curved both upper and lower tooth plates. We hypothesize that: (1) greater disparity between the curvature of the upper and lower jaws will decrease the load necessary to initiate prey fracture (yield load) and (2) occluding a curved tooth surface against a more planar surface is optimal for crushing large prey. Using aluminum stingray jaw replicas fixed to a mechanical loading frame, we measured the forces necessary to fracture uniformly manufactured ceramic tubes as well as two size series, live gastropods (Nucella sp.) and, 3D-printed shell replicas. There was no difference between the two ray species for most of the prey items, but (A) Aetomylaeus performed better when forcing smaller, printed shells to fracture; (B) intermediate shell sizes (printed) required the least amount of force to fracture, followed by smaller shells and then larger ones; (C) Finally, both printed and live shells failed consistently in the same region, at the base of the spire, while ceramic tubes showed greater variation in location of fracture.
