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First published online September 9, 2005
Journal of Experimental Biology 208, 3553-3571 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01816

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Analysis of the bite force and mechanical design of the feeding mechanism of the durophagous horn shark Heterodontus francisci

Daniel R. Huber^1,*, Thomas G. Eason², Robert E. Hueter³ and Philip J. Motta¹

¹ Department of Biology, University of South Florida, 4202 E. Fowler Avenue, SCA 110, Tampa, FL 33620, USA
² Department of Mechanical Engineering, University of South Florida, 4202 E. Fowler Avenue, ENB 118, Tampa, FL 33620, USA
³ Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA

View larger version (25K): [in a new window]   Fig. 1. Left lateral views of representative elasmobranch jaw suspensions. (A) Heterodontus, Heterodontiformes (hyostyly); (B) Heptranchias, Hexanchiformes (amphistyly); (C) Rhinobatos, Batoidea (euhyostyly). Articulation points are marked with arrows. C, ceratohyal; E, ethmoidal; H, hyomandibula; L, lower jaw; O, orbital; P, postorbital; U, upper jaw. Reproduced from Wilga (2002) with permission from Blackwell Publishing.

View larger version (37K): [in a new window]   Fig. 2. Right lateral (A) and ventral (B) views of the cranial and branchial musculature of a 63 cm male H. francisci. CC, coracoarcualis; CH, coracohyoideus; CHD, dorsal hyoid constrictor; CHV, ventral hyoid constrictor; CM, coracomandibularis; CO, coracoid bar; HM, hyomandibulo-mandibularis; IMD, intermandibularis; LH, levator hyomandibularis; LJ, lower jaw; LP, levator palatoquadrati; QM-PO complex, quadratomandibularis-preorbitalis complex; QM-, quadratomandibularis-; PO-, preorbitalis-; UJ, upper jaw; VSBC, ventral superficial branchial constrictor. The IMD has been partially removed to reveal the ventral musculature. The coracobranchiales (not shown) are located deep to the CC.

View larger version (39K): [in a new window]   Fig. 3. (A) Coordinate system for three-dimensional vector analysis of the forces generated by the cranial musculature of H. francisci. Directionality is defined with respect to the head of H. francisci using the `right-hand rule'. (B) Schematic diagram of the jaws of H. francisci indicating variables for mechanical lever-ratio analysis. A-B, resolved in-lever for jaw adduction; A-C, out-lever; B-D, resolved adductive muscle force vector; P0, maximum tetanic tension. CT-scan image used with permission of A. Summers.

View larger version (85K): [in a new window]   Fig. 4. Forces involved in the static equilibrium calculations of the lower and upper jaws of H. francisci. FB, bite reaction force; FE, reaction force at the ethmoidal articulation; FH, reaction force at the hyomandibular articulation; FJR, jaw joint reaction force; FPO-, force generated by the preorbitalis-; FQM-PO, force generated by the quadratomandibularis-preorbitalis complex; FQM-, force generated by the quadratomandibularis-; FR, resultant adductive force; , angle of incidence of FE relative to the articular surface of the upper jaw at the ethmoidal articulation. Arrow size does not indicate force magnitude, and angles of force vectors are approximate. CT-scan image used with permission of A. Summers.

View larger version (99K): [in a new window]   Fig. 5. Theoretical maximum bite force (N) of five male H. francisci (N=5, TL=55-68 cm) from three-dimensional vector analysis of the jaw adducting musculature measured at 0, 25, 50, 75 and 100% of the length of the functional tooth row of the lower jaw from posterior to anterior. CT-scan image used with permission of A. Summers.

View larger version (18K): [in a new window]   Fig. 6. Bite force waveforms from bite performance trials of three male H. francisci (TL=66-70 cm), illustrating in situ voluntary bites with single (black) and double (light gray) force peaks and a bite from a restrained individual (dark gray).

View larger version (14K): [in a new window]   Fig. 7. Maximum in situ bite force (N) from five male H. francisci (TL=63-74 cm) plotted against (A) impulse (kg m s-1) and (B) force duration (ms) on logarithmic axes.

View larger version (20K): [in a new window]   Fig. 8. (A) Bite forces (N) of various vertebrates plotted against mass (g). (B) Residuals from regression analysis of log10 bite force versus log10 mass plotted against log10 mass (g). Broken lines indicate ± 1 standard deviation about the residual mean.

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