Dasyatis americana, the southern stingray

The guitarfish, Rhinobatos lentiginosus

The Evolution of Cephalic Lobes in Batoids
Samantha Mulvany

Five genera of derived rays (Aetobus, Aetomylaeus, Rhinoptera, Mobula, and Manta) possess cephalic lobes, which are modified anterior portions of the pectoral fin, supported by the pectoral girdle and sometimes rostral cartilage.  Many batoids utilize their pectoral fins to help capture and manipulate prey toward their mouth.  Maruska and Tracias (1998) found that D. sabina uses its pectoral fins to not only to pin prey to the substrate, but also to excavate prey from the substrate via swift undulation to displace the sand.  The more derived batoids can also utilize their cephalic lobe(s) to detect prey via electrosensory pores, pin prey to the substrate, and manipulate prey toward their mouth (see the cownose photo above).  While feeding, the eagle ray utilizes its cephalic lobe and modified tooth plates to dig for food in the substrate and pin down prey items to prevent their escape (McCoy et al. 2005). ).  For cownose rays, the cephalic lobes play an integral role in prey detection via electrosensory receptors, excavation, and in feeding behavior, by enclosing the prey to prevent escape (Sasko et al. 2006).   The cephalic lobes are held in a horizontal position during prey detection and are fully depressed during excavation and feeding.

My study aims to compare and contrast the anterior pectoral fin and cephalic lobe morphology and use of a functionally diverse group of batoids using anatomical dissections, radiography, histology, and kinematic studies with high speed videography.  Chosen characters will be mapped onto the existing phylogeny of batoids to investigate the evolutionary patterns of the cephalic lobes.  The species examined include: Rhinoptera bonasus (cownose ray), Aetobatus narinari (spotted eagle ray), Urobatis jamaicensis (yellow stingray) and Dasyatis sabina (Atlantic stingray). The guitarfish Rhinobatos lentiginosus will be used as a representative skate.   While suction feeding, the guitarfish depresses its anterior pectoral fins against the substrate, encapsulating the prey and preventing escape (Wilga and Motta 1998).