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American Zoologist 2001 41(6):1248-1257; doi:10.1093/icb/41.6.1248
© 2001 by The Society for Integrative and Comparative Biology
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Evolution of Upper Jaw Protrusion Mechanisms in Elasmobranchs1

Cheryl D. Wilga2,1, Robert E. Hueter2, Peter C. Wainwright3 and Philip J. Motta4
1 Department of Biological Sciences, University of Rhode Island, 100 Flagg Rd., Kingston, Rhode Island 02881
2 Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, Florida 34236
3 Section of Evolution and Ecology, University of California, One Shields Ave., Davis, California 95616
4 Department of Biology, University of South Florida, Tampa, Florida 33620

Upper jaw protrusion is a prominent component of the feeding mechanism in most elasmobranchs and has received considerable attention over the years. In this paper, we review what is known of muscle activity during prey capture in elasmobranchs, particularly that of upper jaw protrusion, and evaluate the extent to which functional modifications have evolved through changes in anatomy or patterns of muscle activity. To date, motor activity during feeding has been documented in only four species of elasmobranchs, although they represent the three major elasmobranch groups: Galea (typical sharks); Squalea (dogfish sharks); and Batoidea (skates and rays). Our efforts show that while muscles involved in cranial elevation and lower jaw depression and elevation show a conserved pattern of motor activity and function across species, other muscles show a more variable history. Our observations of elasmobranch upper jaw protrusion mechanisms suggest a mosaic of character changes over the course of evolution that involve anatomical changes in all cases and modifications of muscle activation patterns in some cases. During the evolution of feeding mechanisms of elasmobranchs, there have been two structural changes incorporating a pre-existing motor pattern to yield an unmodified kinematic profile, the original preorbitalis and the descendent preorbitalis. One additional instance of structural modification is accompanied by an alteration in the motor pattern leading to a change in movement pattern, the levator palatoquadrati.


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