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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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Regressions of canine bite force against skull width and basal skull length in carnivorous mammals.(A) Regressions of log10-transformed canine bite forces against log10 skull width and (B) regressions of log10-transformed canine bite forces against log10 basal skull length, in carnivorous mammals. Canine bite force values are compiled from Wroe et al. (2005), and listed in Table 3. Isometric specific tension is 30 N/cm2. Basilosaurus isis (blue diamond) has a slightly greater FEA-estimated bite force at the caniniform I2 (at the same anterior position as the canine in most carnivorous mammals) than expected from the skull width equation (A), but lower force than expected from its skull length (B). Note that these values fall well within 95% confidence intervals for the entire sample, suggesting that B. isis did not have exceptionally high or low bite force compared with that expected of a mammal with its skull dimensions.
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pone.0118380.g004: Regressions of canine bite force against skull width and basal skull length in carnivorous mammals.(A) Regressions of log10-transformed canine bite forces against log10 skull width and (B) regressions of log10-transformed canine bite forces against log10 basal skull length, in carnivorous mammals. Canine bite force values are compiled from Wroe et al. (2005), and listed in Table 3. Isometric specific tension is 30 N/cm2. Basilosaurus isis (blue diamond) has a slightly greater FEA-estimated bite force at the caniniform I2 (at the same anterior position as the canine in most carnivorous mammals) than expected from the skull width equation (A), but lower force than expected from its skull length (B). Note that these values fall well within 95% confidence intervals for the entire sample, suggesting that B. isis did not have exceptionally high or low bite force compared with that expected of a mammal with its skull dimensions.

Mentions: Fig. 4 shows regressions for mammalian terrestrial carnivores from data in Table 4, and Table 5 compares regression estimates of Basilosaurus bite force with results of FE analyses. FE-estimated forces for B. isis are close to those expected from its skull width at both the caniniform I2 and at its more posterior, actual canine (9.6% and 15.7% greater, respectively, than the expected 9,614 N). However, B. isis’s FEA-estimated canine-position force is 32.5% lower than expected for its skull length and its canine force is 28.8% lower. The FEA-derived forces for B. isis are within the 95% (and even 85%) confidence intervals of the regression (Fig. 4), whereas residuals for many mammals in the initial regressions fall outside these bounds. The simulated forces for B. isis thus are not exceptionally high or low compared with predicted values. The skull width/bite force regression is tighter (R2 = 0.938) than the regression for length/force (R2 = 0.808).


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)

Regressions of canine bite force against skull width and basal skull length in carnivorous mammals.(A) Regressions of log10-transformed canine bite forces against log10 skull width and (B) regressions of log10-transformed canine bite forces against log10 basal skull length, in carnivorous mammals. Canine bite force values are compiled from Wroe et al. (2005), and listed in Table 3. Isometric specific tension is 30 N/cm2. Basilosaurus isis (blue diamond) has a slightly greater FEA-estimated bite force at the caniniform I2 (at the same anterior position as the canine in most carnivorous mammals) than expected from the skull width equation (A), but lower force than expected from its skull length (B). Note that these values fall well within 95% confidence intervals for the entire sample, suggesting that B. isis did not have exceptionally high or low bite force compared with that expected of a mammal with its skull dimensions.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0118380.g004: Regressions of canine bite force against skull width and basal skull length in carnivorous mammals.(A) Regressions of log10-transformed canine bite forces against log10 skull width and (B) regressions of log10-transformed canine bite forces against log10 basal skull length, in carnivorous mammals. Canine bite force values are compiled from Wroe et al. (2005), and listed in Table 3. Isometric specific tension is 30 N/cm2. Basilosaurus isis (blue diamond) has a slightly greater FEA-estimated bite force at the caniniform I2 (at the same anterior position as the canine in most carnivorous mammals) than expected from the skull width equation (A), but lower force than expected from its skull length (B). Note that these values fall well within 95% confidence intervals for the entire sample, suggesting that B. isis did not have exceptionally high or low bite force compared with that expected of a mammal with its skull dimensions.
Mentions: Fig. 4 shows regressions for mammalian terrestrial carnivores from data in Table 4, and Table 5 compares regression estimates of Basilosaurus bite force with results of FE analyses. FE-estimated forces for B. isis are close to those expected from its skull width at both the caniniform I2 and at its more posterior, actual canine (9.6% and 15.7% greater, respectively, than the expected 9,614 N). However, B. isis’s FEA-estimated canine-position force is 32.5% lower than expected for its skull length and its canine force is 28.8% lower. The FEA-derived forces for B. isis are within the 95% (and even 85%) confidence intervals of the regression (Fig. 4), whereas residuals for many mammals in the initial regressions fall outside these bounds. The simulated forces for B. isis thus are not exceptionally high or low compared with predicted values. The skull width/bite force regression is tighter (R2 = 0.938) than the regression for length/force (R2 = 0.808).

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