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Cited by 218Paleontology and Evolutionary BiologyEvolution and Paleontology StudiesComparative Animal Anatomy Studies

Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation

Open access
Erickson, Gregory M., Gignac, Paul M., Steppan, Scott J., Lappin, A. Kristopher, Vliet, Kent A., Brueggen, John D., Inouye, Brian D., Kledzik, David +1 more·2012·PLoS ONE
DOI 10.1371/journal.pone.0031781PMC PMC3303775
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Abstract

BACKGROUND: Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known. METHODOLOGY/PRINCIPAL FINDINGS: We measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research. CONCLUSIONS/SIGNIFICANCE: Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination.

AI snapshot

Written from the paper’s full text.

TL;DR

Erickson et al. measured bite forces and tooth pressures across all 23 extant crocodilian species (83 adults) and found that body mass, not rostral shape, explains nearly all bite-force variation. Crocodilians generate the highest bite forces and tooth pressures known among living animals, with tooth pressures exceeding the shear strength of bone and previously reported maxima.

Key findings

  • Molariform bite forces ranged from 900 to 8,983 N (*Paleosuchus palpebrosus* and *Crocodylus porosus*, respectively); one *C. porosus* individual reached 16,414 N, the highest bite force measured in any animal, exceeding the 4,500 N recorded for spotted hyena.
  • Body mass was the primary determinant of bite force (TIPs: R² = 0.92; PIC: R² = 0.87, p < 0.0001), with a scaling coefficient of 0.708 ± 0.111, not statistically different from isometry (0.667). Rostral proportions explained just 19% of remaining size-standardized phylogenetically corrected variance (2.5% of total variance; p = 0.03).
  • Caniniform tooth pressures ranged from 195 to 1,344 MPa; molariform pressures ranged from 203 to 1,388 MPa. All exceeded the 147 MPa reported for *Dunkleosteus*, some by as much as 17-fold, and all exceeded the 65–71 MPa ultimate shear strength of bone.
  • Tooth pressures scaled positively allometric (caniniform: 0.490 ± 0.203; molariform: 0.553 ± 0.180 vs. isometry 0.000) and were uncorrelated with rostral proportions (PIC R² = 0.001 caniniform; 0.094 molariform). *Gavialis gangeticus* was the only statistical low-force outlier; fossil predictions included 27,531–34,424 N for 6.7 m *C. porosus* and a historical range of 628–102,803 N.

Methods

  • 83 sexually mature adult specimens representing all 23 extant crocodilian species were tested from St. Augustine Alligator Farm Zoological Park and Crocodylus Park; size range was 1.24–4.59 m and 7–531 kg, with multiple individuals for 19 species.
  • Bite forces were recorded using sandwich transducers and a portable charge amplification system; 3–5 bites were recorded per animal and the highest used. Forces were measured at the prominent maxillary molariform tooth, and caniniform forces were inferred by moment calculation. Tooth contact areas came from dental putty molds and epoxy casts indented 1 mm into clay, measured with ImageJ; pressures were force divided by contact area.
  • Analyses used OLS and reduced major axis regressions on log-transformed taxon representative data, raw “TIPs” analyses, and phylogenetically independent contrasts (PIC) based on a re-estimated DNA sequence phylogeny from Gatesy et al. data; K statistics and ancestral-state reconstructions were also used, with statistical significance reported for PICs.

Limitations

  • Stated: competing phylogenetic hypotheses exist and some sub-clade relationships are debated; the tree used is the best available estimate, and exploring other hypotheses was beyond scope. The upper-bound bite-force estimate for *Deinosuchus riograndensis* is more tenuous because the largest fossil specimens greatly exceed the neontological size range studied.
  • Stated: caniniform pressure estimation was not possible for taxa with shed or broken caniniform teeth; initial tooth pressures alone are insufficient to single out durophagous species’ biomechanical import, and rostral shape needs further explanation.
  • Evident from the text and tables: sample sizes are highly uneven, with many species represented by N = 1 (e.g., *Crocodylus intermedius*, *C. mindorensis*, *C. moreletii*, *C. palustris*), and all specimens were captive, conservation, or display animals from two facilities, so wild population variation is not directly sampled, although the paper cites prior captive–wild equivalence for *Alligator mississippiensis*.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1371/journal.pone.0031781

Cites

54 of 54 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

3 of 42 cited sources checked · 2 supported · 0 flagged · accuracy not yet measured

  • Findingown data

    Pressures for some individual crocodilians were as much as 17-fold higher than the highest previously reported for Dunkleosteus.

    “Values for all taxa exceeded the highest reported previously (147 MPa [21,321 psi]) for the giant extinct placoderm fish Dunkleosteus [22]), and pressures for some individuals were as much as 17-fold higher (Table 2).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [22] PS Anderson, 2006, Feeding mechanics and bite force modelling of the skull of <italic>Dunkleosteus terrelli</italic>, an ancient apex predator., Biol Lett source
  • Interpretationcitation

    The biomechanical capacity was also certainly vital to the occupation of near-shore habitats by crocodilians over millennia.

    “It was also certainly vital to the occupation of near-shore habitats by crocodilians over millennia – although prey types changed, the materials of which they were composed did not (e.g. [30]).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [30] GM Erickson, 2002, Evolution of the biomechanical material properties of the femur., Anat Rec source

      The Discussion (page unavailable) examines the evolutionary stability of femoral material properties and briefly reports measurements for crocodilians. It does not address whether biomechanical capacity enabled crocodilians to occupy near-shore habitats, or whether changing prey types retained the same material composition. Searches for near-shore habitats, crocodilian occupation, and prey materials found no passage supporting those points. (LLM, conf=0.72)

      Experimental — accuracy not yet measured
  • Findingown data

    Values for all taxa exceeded the highest reported previously (147 MPa) for the giant extinct placoderm fish Dunkleosteus.

    “Values for all taxa exceeded the highest reported previously (147 MPa [21,321 psi]) for the giant extinct placoderm fish Dunkleosteus [22]), and pressures for some individuals were as much as 17-fold higher (Table 2).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [22] PS Anderson, 2006, Feeding mechanics and bite force modelling of the skull of <italic>Dunkleosteus terrelli</italic>, an ancient apex predator., Biol Lett source
  • Findingown data

    Only in Gavialis gangeticus is there evidence of significant departure in bite-force performance.

    “Only in the extremely slender-snouted Gavialis gangeticus, arguably the only truly piscivorous species, is there evidence of significant departure in performance, and this is reflected in their anatomy.”
    Quote in the paperSubstantial claim
  • Findingown data

    Only the forces for Gavialis gangeticus in the TIPS analysis are significantly atypical (lower) than those of extant Crocodylia as a whole.

    “Only the forces for Gavialis gangeticus in the TIPS analysis are significantly atypical (lower) than those of extant Crocodylia as a whole (Figure 3A).”
    Quote in the paperNot a substantial claim
  • May combine two claims. 29
  • Classified as probably not a substantial claim. 16

  • May combine two claims.

    Findingreasoning

    The crocodilian musculo-cranial design allows for the generation of prodigious bite forces across a broad range of sizes, with Gavialis gangeticus as an exception.

    “The crocodilian musculo-cranial design allows for the generation of prodigious bite forces across a broad range of sizes (Gavialis gangeticus is the exception; see above).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The RMA scaling coefficient for log-transformed taxon representative caniniform tooth pressure regressed against log-transformed body mass is 0.490±0.203 (95% CI), greater than isometry (0.000), and did not support the hypothesis.

    “The RMA scaling coefficient for log-transformed taxon representative caniniform tooth pressure regressed against log-transformed body mass was 0.490±0.203 (95% CI), which is greater (i.e. positively allometric) than isometry (scaling coefficient = 0.000), and so did not support our hypothesis.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Caniniform tooth pressures trend positively with increasing body mass, but are highly variable (TIPs R2 = 0.20; PIC R2 = 0.19, p = 0.09).

    “These values also trend positively with increasing body mass, but are highly variable (TIPs: R2 = 0.20; PIC: R2 = 0.19, p = 0.09).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Body size accounts for nearly all interspecific variance in adult crocodilian bite-force capacity, and these forces scale isometrically to body mass.

    “Body size actually accounts for nearly all interspecific variance in adult crocodilian bite-force capacity, and these forces scale isometrically to body mass.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Size-standardized caniniform tooth pressures changed independently on multiple lineages and were uncorrelated with rostral proportions (PIC R2 = 0.001).

    “Size-standardized caniniform tooth pressures changed independently on multiple lineages (Figure 4B) and were uncorrelated with rostral proportions (PIC R2 = 0.001; Figure 5A).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    All other crocodilian ecomorphs (molluscivores, terrestrial foragers, broad-snouted generalists, and slender-snouted generalists such as Tomistoma schlegelii and Crocodylus acutus) show similar caniniform pressure values to each other that are relatively lower.

    “All other crocodilian ecomorphs (molluscivores, terrestrial foragers, broad-snouted generalists, and the slender-snouted generalists – such as Tomistoma schlegelii and the American crocodile – Crocodylus acutus [1], [7]) show similar values to each other that are relatively lower.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [1] G Webb, 1989, Crocodiles of Australia

      Not checked in the free run.

    • cites [7] AC Pooley, 1989, Food and feeding habits.

      Not checked in the free run.

  • May combine two claims.

    Findingown data

    Size-standardized molariform tooth pressures changed repeatedly in the phylogeny and were not significantly correlated with rostral proportions (PIC R2 = 0.094).

    “Size-standardized molariform tooth pressures changed repeatedly in the phylogeny (Figure 6B) and were not significantly correlated with rostral proportions (PIC R2 = 0.094; Figure 5B).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    No molariform tooth-pressure values are statistical outliers, and no definitive ecomorphological groupings exist.

    “No values are statistical outliers, and no definitive ecomorphological groupings exist.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The RMA scaling coefficient for log-transformed taxon representative bite force regressed against log-transformed body mass is 0.708±0.111 (95% CI), not statistically different from isometry (0.667).

    “The reduced major axis (RMA) scaling coefficient for log-transformed taxon representative bite force regressed against log-transformed body mass was 0.708±0.111 (95% CI), which is not statistically different from isometry (scaling coefficient = 0.667).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The RMA scaling coefficient for log-transformed taxon representative molariform tooth pressures regressed against log-transformed body mass is 0.553±0.180 (95% CI), greater than isometry (0.000), and did not support the hypothesis.

    “The RMA scaling coefficient for log-transformed taxon representative molariform tooth pressures regressed against log-transformed body mass was 0.553±0.180 (95% CI), which is greater (i.e. positively allometric) than isometry (scaling coefficient = 0.000), and therefore did not support our hypothesis.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingnone given

    Caniniform pressure values for Crocodylus johnsoni are moderately high.

    “The values for Crocodylus johnsoni are moderately high.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    One Crocodylus porosus individual measured 16,414 N, representing the highest bite force measured in any animal.

    “(Our datum for one Crocodylus porosus individual, 16,414 N [3,689 lbs] represents the highest bite force measured in any animal.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Molariform pressures for Crocodylus johnsoni and Crocodylus intermedius are relatively high, and those for Crocodylus palustris and Crocodylus moreletii are relatively low.

    “Nevertheless, those for the slender-snouted Crocodylus johnsoni and Crocodylus intermedius are relatively high, and those for the broader-snouted generalists, the mugger (Crocodylus palustris), and Morelet's crocodile (Crocodylus moreletii) are relatively low.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingnone given

    None of the molariform pressure values are statistical outliers.

    “None of the molariform pressure values are statistical outliers.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Body mass is the primary determinant of crocodilian force generation in both raw data analysis (TIPs R2 = 0.92) and phylogenetically corrected analysis (PIC R2 = 0.87, p<0.0001).

    “Body mass is the primary determinant of crocodilian force generation in both the raw data analysis (TIPs: R2 = 0.92) and phylogenetically corrected analysis (PIC: R2 = 0.87, p<0.0001).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The prominent molariform tooth position is at a comparable relative distance from the fulcrum across taxa, with a scaling coefficient of 0.342±0.029 (95% CI) that is not different from isometry at 0.333.

    “Fortuitously the prominent molariform tooth position is at a comparable relative distance from the fulcrum across taxa, as an RMA plot of log-transformed fulcrum to molariform distance regressed against log-transformed body mass showed a scaling coefficient of 0.342±0.029 (95% CI), which is not different than isometry at 0.333.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Findingown data

    All searches found the same single tree, congruent with the slightly less resolved tree in Gatesy et al. and identical to Gatesy and Amato except for resolving one trichotomy near the tip in Crocodylus.

    “All searches found the same single tree (Figure 1), congruent with the slightly less resolved tree in Gatesy et al. [2], and identical to that in the more recent Gatesy and Amato [45] analysis with the exception of our tree resolving one trichotomy near the tip in Crocodylus.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [2] J Gatesy, 2004, Inconsistencies in arguments for the supertree approach: supermatrices versus supertrees of Crocodylia., Sys Bio source
    • cites [45] J Gatesy, 2008, The rapid accumulation of consistent molecular support for intergeneric crocodilian relationships., Molec Phylog Evol source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Findingown data

    A smoothing parameter value of 3.2 minimized deviations and was used in the final analysis.

    “A smoothing parameter value of 3.2 was found to minimize deviations and was the value used in the final analysis.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Bite force was strongly correlated with body mass for both raw data (R2=0.92) and phylogenetically corrected log-transformed data (R2=0.87).

    “Since bite force was strongly correlated with body mass for both raw data (R2 = 0.92) and phylogenetically corrected log-transformed data (R2 = 0.87), we first created size-standardized variables.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Adult body sizes and cranio-dental anatomy are conspicuously variable among crocodilian species.

    “Conversely adult body sizes and cranio-dental anatomy are conspicuously variable [3], [6] (Figure 1).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [3] CA Brochu, 2001, Crocodylian snouts in space and time: phylogenetic approaches toward adaptive radiation., Amer Zool source
    • cites [6] CA Brochu, 2003, Phylogenetic approaches toward crocodylian history., Ann Rev Ear Plan Sci source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    Multiple individuals were studied for 19 species.

    “Multiple individuals were studied for 19 species (Table 1).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable).

    Interpretationown data

    The data and methods from this study provide the quantitative biomechanical foundation for further exploration of the evolutionary success of crocodilians.

    “Collectively, the data and methods from this study provide the quantitative biomechanical foundation for further exploration (particularly in fossil taxa) of the remarkable evolutionary success of these long-term predatory denizens of the water-land interface.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    Catastrophic failure of prey tissues is induced either by driving cracks at the point of tooth engagement or by causing structural failure away from the point(s) of tooth engagement due to bite force alone.

    “Catastrophic failure of the prey's tissues is subsequently induced either by driving cracks [21] at the point of tooth engagement (the damage being more expansive in the stoutest-toothed forms), or by causing structural failure away from the point(s) of tooth engagement due to bite force alone.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [21] PW Lucas, 2004, Dental Functional Morphology: How Teeth Work source

  • May combine two claims.

    Interpretationnone given

    Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces.

    “Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    The reason for similar peak pressures in caniniform and molariform teeth is that both tooth types are composed of the same dental constituents (enamel and von Ebner's dentine) and must be able to damage, and yet sustain impacts with the same tissue types when feeding.

    “We suspect the reason for the similarity is that both tooth types are composed of the same dental constituents (enamel and von Ebner's dentine) and must be able to damage, and yet sustain impacts with the same tissue types when feeding.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductcitation

    The study accessed 83 adult sexually mature specimens representing all 23 extant crocodilian species recognized by the IUCN-SSC Crocodile Specialist Group, with a size range of 1.24-4.59 m and 7-531 kg.

    “In total 83 adult (sexually mature) specimens representing all 23 extant crocodilian species currently recognized by the IUCN-SSC (Species Survival Commission of the International Union for Conservation) Crocodile Specialist Group ([23]; size range 1.24–4.59 m, 7–531 kg) were accessed.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [23] FW King, 1989, Crocodilian, Tuatara and Turtle Species of the World: A Taxonomic Reference

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    No animals were injured during the execution of the research.

    “No animals were injured during the execution of this research.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Spurious correlations were avoided by examining the effects of phylogenetic relationships using independent contrasts.

    “Spurious correlations were avoided by examining the effects of phylogenic relationships using independent contrasts.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Enhanced jaw-closing performance in Gavialis gangeticus was likely afforded at the cost of diminished bite-force capacity, consistent with empirical findings for molariform and estimated caniniform bite forces.

    “This enhanced jaw-closing performance was likely afforded at the cost of diminished bite-force capacity, which is consistent with our empirical findings for both molariform and estimated caniniform bite forces in Gavialis gangeticus.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Gavialis gangeticus independently evolved extremely hypertrophied, low-mechanical advantage adductor mandibulae muscles, and small, fusiform-fibered posterior pterygoid muscles that presumably accentuate rapid jaw closure.

    “These low-force biters independently evolved extremely hypertrophied, low-mechanical advantage adductor mandibulae muscles, and small, fusiform-fibered posterior pterygoid muscles that presumably accentuate rapid jaw closure [17], [19].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [17] NN Iordansky, 1964, The jaw muscles of the crocodiles and some relating structures of the crocodilian skull., Anat Anz
    • cites [19] H Endo, 2002, Comparative functional morphology of the masticatory apparatus in the long-snouted crocodiles., Anat Histol Embr source

  • May combine two claims.

    Interpretationreasoning

    Molariform teeth are well suited for enduring higher resistance forces while generating pressures initially sufficient to damage hard constituents in prey.

    “Because the molariform teeth are stouter, they are well suited for enduring higher resistance forces while at the same time generating pressures that, like the caniniform teeth, are initially sufficient to damage the hard constituents in their prey.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    The study was carried out in accordance with the NIH Guide for the Care and Use of Laboratory Animals and was approved by the Florida State University Animal Care and Use Committee (Permit Number 0011).

    “This study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The research protocol was approved by the Animal Care and Use Committee of The Florida State University (Permit Number: 0011).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationcitation

    The conceptual model leaves rostral shape to be explained more fully by its relevance to the positioning and numbers of teeth, jaw hydrodynamics, and resistance to torsion or bending during prey capture and processing.

    “Our conceptual model leaves rostral shape, which is obviously very important with regard to the crocodilian diversification, to be explained more fully by its relevance to the positioning and numbers of teeth, jaw hydrodynamics, and resistance to torsion or bending during prey capture and processing [11].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [11] SE Pierce, 2008, Patterns of morphospace occupation and mechanical performance in extant crocodilian skulls: a combined geometric morphometric and finite element modeling approach., J Morph source

  • May combine two claims.

    Interpretationreasoning

    More slender-snouted crocodilian forms will experience higher stresses to their jaws because they have lower area moments of inertia with which to resist bending.

    “A consequence of this is that more slender-snouted forms will at the same time experience higher stresses to their jaws since they have lower area moments of inertia with which to resist bending.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The hypothesis that crocodilian rostral proportions positively correlate with bite-force capacity, while statistically significant (p = 0.03), is not supported as a major predictor of force even after correcting for size.

    “Thus, the hypothesis that crocodilian rostal proportions positively correlate with bite-force capacity, while statistically significant (p = 0.03), is not supported as a major predictor of force even after correcting for size.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Slender-snouted crocodilian species sustain bite forces typical of more robust-snouted crocodilians by targeting small prey relative to their size whose low inertia contributes little to resistance forces.

    “We suspect the answer lies primarily in their prey selection. They target small prey relative to their size (e.g. fish and crustaceans, and/or birds and small mammals by the larger species) whose low inertia contributes little to resistance forces.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    No sequence data were available for Caiman yacare, so it was excluded from the phylogeny and subsequent phylogenetic independent contrasts but included in raw TIPs analyses.

    “No sequence data were available for Caiman yacare, and so it was not included in the phylogeny, nor in subsequent phylogenetic independent contrasts (PIC). (Note: it was, however, included in analyses of the raw [TIPs] data.)”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    For the same four taxa with intraspecific body-size ranges greater than 70% of the largest individual's size, scaling effects on contact area were accounted for using power-law modeling.

    “For the same four taxa in which the range of intraspecific body size was greater than 70% of the largest individual's size (see above), we accounted for scaling effects on contact area using power-law modeling.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Shearing is the primary means of failure for hard materials in biological systems.

    “shearing is the primary means of failure for hard materials in biological systems [29].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [29] DR Carter, 2001, Skeletal Function and Form: Mechanobiology of Skeletal Development, Aging, and Regeneration

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    The effective bite force applied during sub-aquatic or terrestrial clenching bites would be unaffected by drag.

    “The effective bite force applied during sub-aquatic or terrestrial clenching bites [i.e. where the bite-force transducer or prey has already been seized and a new bite initiated] would be unaffected by drag.”
    Quote in the paperNot a substantial claim
40 of 40

  • The paper relies on this without support.

    Extinct crocodilians followed the same body-mass-to-bite-force scaling relationship as extant species, so regression equations from extant taxa can predict fossil bite forces.

    “Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research.”
    “Crocodilian bite-force retention can be used to predict forces in other specimens and species, including taxa known only from fossils (see Materials and Methods).”

  • The paper relies on this without support.

    Crocodilians typically bite unilaterally, so the crowns of the prominent caniniform teeth initiate contact with prey during biting.

    “Because of their greater length relative to the adjacent teeth, and the propensity of crocodilians to bite unilaterally, the crowns of these teeth typically initiate contact with prey during biting.”

  • The paper relies on this without support.

    The caniniform and molariform teeth of crocodilians are composed of the same dental constituents, enamel and von Ebner's dentine.

    “We suspect the reason for the similarity is that both tooth types are composed of the same dental constituents (enamel and von Ebner's dentine) and must be able to damage, and yet sustain impacts with the same tissue types when feeding.”

  • The paper relies on this without support.

    The prominent molariform tooth position is where crocodilians primarily crush prey.

    “This is an ecologically relevant location since it is where these animals primarily crush prey.”

  • The paper relies on this without support.

    Crocodilians stereotypically seize prey contacted by the teeth and jaws as the head is swiped to the side.

    “Crocodilians stereotypically seize prey contacted by the teeth and jaws as the head is swiped to the side.”

  • The paper relies on this without support.

    Crocodilians process food on one side of the jaw.

    “They also process food on one side of the jaw.”

  • The paper relies on this without support.

    Unilateral crushing of prey at the molariform teeth commonly occurs with the head out of water in all species.

    “Additionally, unilateral crushing of prey at the molariform teeth commonly occurs with the head out of water in all species.”

  • The paper relies on this without support.

    Seizing of prey using the caniniform teeth often occurs with the head out of water.

    “Similarly, the seizing of prey using the caniniform teeth often occurs with the head out of water.”
8 of 8

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Large saltwater-crocodile bite-force estimate conflicts with the stated regression

    Major

    The stated interspecific equation gives 29.632 × 1,308 + 569.35 = 39,328 N for the stated mass. That exceeds the reported upper estimate of 34,424 N, even though the paper says this regression was used to establish the range.

  • Tomistoma representative contact area exceeds its reported range

    Minor

    Table 2 gives a representative caniniform contact area of 2.99 mm2, but its reported range is only 1.72-1.84 mm2.

  • Melanosuchus mean length conflicts with its length-range entry

    Minor

    Table 1 reports a mean total length of 246 cm but gives 304 cm as the range-of-total-lengths entry. A range containing only 304 cm cannot encompass a mean of 246 cm.

3 of 3

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Authors
Erickson, G. M., Gignac, P. M., Steppan, S. J., Lappin, A. K., Vliet, K. A., Brueggen, J. D., Inouye, B. D., Kledzik, D., & Webb, G. J. W.
Affiliations
  • Florida State University (US)
  • California State Polytechnic University (US)
  • University of Florida (US)
  • Charles Darwin University (AU)
Corresponding author
Erickson, Gregory M.
ORCID
Venue
PLoS ONE
Publisher
Public Library of Science (PLoS)
Published
2012-03-14
Volume
7
Issue
3
Pages
e31781
ISSN
1932-6203 (ISSN-L)
DOI
10.1371/journal.pone.0031781
PMC
PMC3303775
OpenAlex
W2048410549
Semantic Scholar
6c10b5a18592760e865f3efdb6382f3e8f89d3a4
Cited by
218
References
52
Citations by year
2026: 13 · 2025: 10 · 2024: 16 · 2023: 8 · 2022: 16 · 2021: 27 · 2020: 16 · 2019: 28 · 2018: 10 · 2017: 17 · 2016: 14 · 2015: 15 · 2014: 13 · 2013: 11 · 2012: 4
FWCI
10.25
Type
journal article
Language
en
Open access
Licence
Locations
  • PLoS ONE (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • CDU eSpace Institutional Repository (Charles Darwin University) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Science Foundation (0841447, 0959029, 0623791)
  • National Geographic Society
Topics
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Evolutionary Biology
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
  • Health Sciences › Medicine › Urology › Comparative Animal Anatomy Studies
Keywords
crocodilians, bite force, feeding mechanics, jaw morphology, body size, feeding evolution, fossil crocodilians, phylogenetic analysis, evolutionary success
MeSH terms
Alligators and Crocodiles, Animals, Biomechanical Phenomena, Bite Force, Body Weight, Biological Evolution, Jaw, Molar, Phylogeny, Predatory Behavior, Pressure, Skull, Tooth, Linear Models, Extinction, Biological, Ecological and Environmental Phenomena

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-28.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-28.

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