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Bone-breaking bite force of Basilosaurus isis (Mammalia, Cetacea) from the late Eocene of Egypt estimated by finite element analysis.

Snively E, Fahlke JM, Welsh RC - PLoS ONE (2015)

Bottom Line: The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion.Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs.Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, Wisconsin, United States of America.

ABSTRACT
Bite marks suggest that the late Eocence archaeocete whale Basilosaurus isis (Birket Qarun Formation, Egypt) fed upon juveniles of the contemporary basilosaurid Dorudon atrox. Finite element analysis (FEA) of a nearly complete adult cranium of B. isis enables estimates of its bite force and tests the animal's capabilities for crushing bone. Two loadcases reflect different biting scenarios: 1) an intitial closing phase, with all adductors active and a full condylar reaction force; and 2) a shearing phase, with the posterior temporalis active and minimized condylar force. The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion. Reaction forces with all muscles active indicate that B. isis maintained relatively greater bite force anteriorly than seen in large crocodilians, and exerted a maximum bite force of at least 16,400 N at its upper P3. Under the shearing scenario with minimized condylar forces, tooth reaction forces could exceed 20,000 N despite lower magnitudes of muscle force. These bite forces at the teeth are consistent with bone indentations on Dorudon crania, reatract-and-shear hypotheses of Basilosaurus bite function, and seizure of prey by anterior teeth as proposed for other archaeocetes. The whale's bite forces match those estimated for pliosaurus when skull lengths are equalized, suggesting similar tradeoffs of bite function and hydrodynamics. Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs. However, comparison of force estimates from FEA and regression data indicate that B. isis exerted the largest bite forces yet estimated for any mammal, and greater force than expected from its skull width. Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation.

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Jaw muscles of Basilosaurus isis and constraints for FEA.A. Jaw muscles of B. isis and muscle vector and moment arms for leverage-based force calculation. B. Adductors (red arrows) mapped onto a CT-based finite element model of the cranium of Basilosaurus isis WH-74, including the dentaries. C. Constraints for finite element analyses. In the all-muscles active analysis, the cranium was fully constrained at the left and right temporomandibular joints (TMJ), and tooth constraints were applied in respective bite analyses. In the posterior shear analysis, the only active muscles are the posterior temporalis, and only P3 is constrained.
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pone.0118380.g001: Jaw muscles of Basilosaurus isis and constraints for FEA.A. Jaw muscles of B. isis and muscle vector and moment arms for leverage-based force calculation. B. Adductors (red arrows) mapped onto a CT-based finite element model of the cranium of Basilosaurus isis WH-74, including the dentaries. C. Constraints for finite element analyses. In the all-muscles active analysis, the cranium was fully constrained at the left and right temporomandibular joints (TMJ), and tooth constraints were applied in respective bite analyses. In the posterior shear analysis, the only active muscles are the posterior temporalis, and only P3 is constrained.

Mentions: With its enormous skull and body size, Basilosaurus is an outlier among carnivorous mammals for which bite force data are available. Thus, we compare our modeled bite force with estimates for other mammals [26], [29] to test whether B. isis had a particularly forceful bite for a mammal with its skull dimensions. Previous bite force estimates are based on diverse methods, including the dry skull method [25] and FEA, and comparisons among these modeled estimates warrant caution. Notably, dry skull mammal studies present a comprehensive and rigorous database of bite force estimates, and these estimates are only slightly lower than FEA results, which have muscle forces distributed across attachments 27], [36], [37] rather than between estimated centers of pull [25], [26], [29]. The current study’s bite force comparisons between B. isis and other mammals will therefore be worthwhile and testable by applying FEA [28], [30], [31] to more carnivorous mammals in Wroe and colleagues’ original results [26]. We construct a simple lever model of B. isis (Fig. 1) to check correspondence between simplified dry skull and 3D FEA approaches.


Bone-breaking bite force of Basilosaurus isis (Mammalia, Cetacea) from the late Eocene of Egypt estimated by finite element analysis.

Snively E, Fahlke JM, Welsh RC - PLoS ONE (2015)

Jaw muscles of Basilosaurus isis and constraints for FEA.A. Jaw muscles of B. isis and muscle vector and moment arms for leverage-based force calculation. B. Adductors (red arrows) mapped onto a CT-based finite element model of the cranium of Basilosaurus isis WH-74, including the dentaries. C. Constraints for finite element analyses. In the all-muscles active analysis, the cranium was fully constrained at the left and right temporomandibular joints (TMJ), and tooth constraints were applied in respective bite analyses. In the posterior shear analysis, the only active muscles are the posterior temporalis, and only P3 is constrained.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340796&req=5

pone.0118380.g001: Jaw muscles of Basilosaurus isis and constraints for FEA.A. Jaw muscles of B. isis and muscle vector and moment arms for leverage-based force calculation. B. Adductors (red arrows) mapped onto a CT-based finite element model of the cranium of Basilosaurus isis WH-74, including the dentaries. C. Constraints for finite element analyses. In the all-muscles active analysis, the cranium was fully constrained at the left and right temporomandibular joints (TMJ), and tooth constraints were applied in respective bite analyses. In the posterior shear analysis, the only active muscles are the posterior temporalis, and only P3 is constrained.
Mentions: With its enormous skull and body size, Basilosaurus is an outlier among carnivorous mammals for which bite force data are available. Thus, we compare our modeled bite force with estimates for other mammals [26], [29] to test whether B. isis had a particularly forceful bite for a mammal with its skull dimensions. Previous bite force estimates are based on diverse methods, including the dry skull method [25] and FEA, and comparisons among these modeled estimates warrant caution. Notably, dry skull mammal studies present a comprehensive and rigorous database of bite force estimates, and these estimates are only slightly lower than FEA results, which have muscle forces distributed across attachments 27], [36], [37] rather than between estimated centers of pull [25], [26], [29]. The current study’s bite force comparisons between B. isis and other mammals will therefore be worthwhile and testable by applying FEA [28], [30], [31] to more carnivorous mammals in Wroe and colleagues’ original results [26]. We construct a simple lever model of B. isis (Fig. 1) to check correspondence between simplified dry skull and 3D FEA approaches.

Bottom Line: The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion.Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs.Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, Wisconsin, United States of America.

ABSTRACT
Bite marks suggest that the late Eocence archaeocete whale Basilosaurus isis (Birket Qarun Formation, Egypt) fed upon juveniles of the contemporary basilosaurid Dorudon atrox. Finite element analysis (FEA) of a nearly complete adult cranium of B. isis enables estimates of its bite force and tests the animal's capabilities for crushing bone. Two loadcases reflect different biting scenarios: 1) an intitial closing phase, with all adductors active and a full condylar reaction force; and 2) a shearing phase, with the posterior temporalis active and minimized condylar force. The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion. Reaction forces with all muscles active indicate that B. isis maintained relatively greater bite force anteriorly than seen in large crocodilians, and exerted a maximum bite force of at least 16,400 N at its upper P3. Under the shearing scenario with minimized condylar forces, tooth reaction forces could exceed 20,000 N despite lower magnitudes of muscle force. These bite forces at the teeth are consistent with bone indentations on Dorudon crania, reatract-and-shear hypotheses of Basilosaurus bite function, and seizure of prey by anterior teeth as proposed for other archaeocetes. The whale's bite forces match those estimated for pliosaurus when skull lengths are equalized, suggesting similar tradeoffs of bite function and hydrodynamics. Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs. However, comparison of force estimates from FEA and regression data indicate that B. isis exerted the largest bite forces yet estimated for any mammal, and greater force than expected from its skull width. Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation.

Show MeSH
Related in: MedlinePlus