Meeting Abstract
Durophagous predators consume hard-shelled prey items such as bivalves, gastropods and large crustaceans. Most of them mechanically crush heavily mineralized prey. This is expensive both from the point of view of the bite forces involved and the stresses inflicted on the predator’s skeleton. It is quite common for durophagous taxa to shift from softer prey to hard prey at some point in ontogeny, implying that it is relatively harder for small animals to crush their way into prey. Batoid fishes (rays, skates, sawfishes and guitarfishes) have independently evolved durophagy multiple times, despite the challenges associated with crushing prey harder than their own cartilaginous skeleton. Potamotrygon leopoldi is a durophagous freshwater ray endemic to the Xingu River Basin in Brazil, with a jaw morphology superficially similar to that of distant relatives, like eagle rays (Aetomylaeus). We examined how the resistance to bending and mineralization of the jaws changed over ontogeny in P. leopoldi (n = 5, 14-45 cm disc width), using computed tomography (CT) scanning to calculate the 2nd moment of area of the jaws. P. leopoldi has lower jaw stiffness relative to other durophagous elasmobranchs and the skeleton nearest the jaw joints is stiffer than that beneath the dentition. While jaw stiffness has similar material distribution over ontogeny, mineralization under the teeth increases. Neonate rays have low jaw stiffness and poor mineralization, suggesting that P. leopoldi may not feed on hard prey early in life. These differences in the shape, stiffness and mineralization of the jaws of P. leopoldi compared to its distant durophagous relatives suggest there are many solutions for crushing hard prey with a soft skeleton.
