Carroll, A.M.*; Wainwright, P.C.: Functional morphology of prey capture in the pallid sturgeon (Scaphirhynchus albus).

We examined the anatomical and kinematic basis of prey capture in sturgeon. Sturgeon (Acipenseridae) are a basal actinopterygians with a highly derived cranial morphology. Despite their anatomical singularity and phylogenetic significance, no functional study of the kinematics of sturgeon feeding has been published. Feeding pallid sturgeon (Scaphirhynchus albus) were filmed in lateral and ventral views at 250 frames per second. Feeding events were characterized by jaw opening, jaw protrusion, caudal-ventral retraction of the hyoid, ventral expansion of the branchial basket, and adduction followed by abduction of the opercular margin. Prey items were drawn into open jaws which were closed after prey entry, indicating that sturgeon feed by suction rather than biting. Evidence from muscle stimulation and anatomy support previously published hypotheses about the muscular basis of feeding kinematics. The sturgeon’s jaws are not directly connected to its neurocranium, but are suspended from the hyoid arch and may be protruded ventrally. Protrusion is powered by the protractor hyomandibularis muscle which rotates the hyomandibula rostrally at its articulation to the neurocranium. This rostral rotation is transmitted to the jaws, which are deflected ventrally by the ventrally sloping underside of the neurocranium. This mechanism of jaw protrusion is unique to the order Acipenseriformes. The robust sternohyoideus drives hyoid retraction, jaw opening, and branchial basket expansion. Jaw opening by the sternohyoideus is the hypothesized ancestral jaw opening mechanism for actinopterygians. Despite the morphological differences between sturgeon and other lineages the kinematics of sturgeon feeding are essentially similar to other aquatic-feeding gnathostomes.