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Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation.

Erickson GM, Gignac PM, Steppan SJ, Lappin AK, Vliet KA, Brueggen JD, Inouye BD, Kledzik D, Webb GJ - PLoS ONE (2012)

Bottom Line: Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture.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.The biomechanical and ecological ramifications of such changes need further examination.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America. gerickson@bio.fsu.edu

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.

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Molariform pressure values for extant Crocodylia, their phylogenetic distribution, and inferred ancestral character states.(A) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the relationship between body size and molariform pressure. Note that the range of values shows similar interspecific correspondence to the caniniform pressure data shown in Figure 4A. The arrow indicates the typical ultimate shear strength of bone. (B) Ancestral-state reconstruction using squared-change parsimony of size-standardized molariform pressures. Pressures are color coded to MPa. Vertical scale is in relative time, with the outgroup/ingroup root arbitrarily set to 1.0. The notable similarities between unrelated taxa and differences between related taxa illustrate the large amount of convergence for this trait among crocodilians.
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pone-0031781-g006: Molariform pressure values for extant Crocodylia, their phylogenetic distribution, and inferred ancestral character states.(A) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the relationship between body size and molariform pressure. Note that the range of values shows similar interspecific correspondence to the caniniform pressure data shown in Figure 4A. The arrow indicates the typical ultimate shear strength of bone. (B) Ancestral-state reconstruction using squared-change parsimony of size-standardized molariform pressures. Pressures are color coded to MPa. Vertical scale is in relative time, with the outgroup/ingroup root arbitrarily set to 1.0. The notable similarities between unrelated taxa and differences between related taxa illustrate the large amount of convergence for this trait among crocodilians.

Mentions: Taxon representative molariform tooth-pressure values ranged from 203 to 1,388 MPa (29,443 to 201,312 psi) (Dwarf crocodile – Osteolaemus tetraspis, and Crocodylus intermedius, respectively; Table 2, Figure 6A). These are more strongly correlated with body mass than the caniniform data (TIPs: R2 = 0.54; PIC: R2 = 0.293, p = 0.008). 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. None of the molariform pressure values are statistical outliers. 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. Pressures for all other ecomorphs, including Gavialis gangeticus, are comparable. 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).


Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation.

Erickson GM, Gignac PM, Steppan SJ, Lappin AK, Vliet KA, Brueggen JD, Inouye BD, Kledzik D, Webb GJ - PLoS ONE (2012)

Molariform pressure values for extant Crocodylia, their phylogenetic distribution, and inferred ancestral character states.(A) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the relationship between body size and molariform pressure. Note that the range of values shows similar interspecific correspondence to the caniniform pressure data shown in Figure 4A. The arrow indicates the typical ultimate shear strength of bone. (B) Ancestral-state reconstruction using squared-change parsimony of size-standardized molariform pressures. Pressures are color coded to MPa. Vertical scale is in relative time, with the outgroup/ingroup root arbitrarily set to 1.0. The notable similarities between unrelated taxa and differences between related taxa illustrate the large amount of convergence for this trait among crocodilians.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3303775&req=5

pone-0031781-g006: Molariform pressure values for extant Crocodylia, their phylogenetic distribution, and inferred ancestral character states.(A) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the relationship between body size and molariform pressure. Note that the range of values shows similar interspecific correspondence to the caniniform pressure data shown in Figure 4A. The arrow indicates the typical ultimate shear strength of bone. (B) Ancestral-state reconstruction using squared-change parsimony of size-standardized molariform pressures. Pressures are color coded to MPa. Vertical scale is in relative time, with the outgroup/ingroup root arbitrarily set to 1.0. The notable similarities between unrelated taxa and differences between related taxa illustrate the large amount of convergence for this trait among crocodilians.
Mentions: Taxon representative molariform tooth-pressure values ranged from 203 to 1,388 MPa (29,443 to 201,312 psi) (Dwarf crocodile – Osteolaemus tetraspis, and Crocodylus intermedius, respectively; Table 2, Figure 6A). These are more strongly correlated with body mass than the caniniform data (TIPs: R2 = 0.54; PIC: R2 = 0.293, p = 0.008). 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. None of the molariform pressure values are statistical outliers. 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. Pressures for all other ecomorphs, including Gavialis gangeticus, are comparable. 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).

Bottom Line: Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture.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.The biomechanical and ecological ramifications of such changes need further examination.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America. gerickson@bio.fsu.edu

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.

Show MeSH
Related in: MedlinePlus