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The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae)

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The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae). / Cox, Philip Graham.

In: PeerJ, Vol. 5, No. 8, 3741, 30.08.2017, p. e3741.

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Harvard

Cox, PG 2017, 'The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae)', PeerJ, vol. 5, no. 8, 3741, pp. e3741. https://doi.org/10.7717/peerj.3741

APA

Cox, P. G. (2017). The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae). PeerJ, 5(8), e3741. [3741]. https://doi.org/10.7717/peerj.3741

Vancouver

Cox PG. The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae). PeerJ. 2017 Aug 30;5(8):e3741. 3741. https://doi.org/10.7717/peerj.3741

Author

Cox, Philip Graham. / The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae). In: PeerJ. 2017 ; Vol. 5, No. 8. pp. e3741.

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@article{e9038e26368f43f2bbb93eedf52b0721,
title = "The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae)",
abstract = "The mammalian jaw is often modelled as a third-class lever for the purposes of biomechanical analyses, owing to the position of the resultant muscle force between the jaw joint and the teeth. However, it has been proposed that in some rodents the jaws operate as a second-class lever during distal molar bites, owing to the rostral position of the masticatory musculature. In particular, the infraorbital portion of the zygomatico-mandibularis (IOZM) has been suggested to be of major importance in converting the masticatory system from a third-class to a second-class lever. The presence of the IOZM is diagnostic of the hystricomorph rodents, and is particularly well-developed in Pedetes capensis, the South African springhare. In this study, finite element analysis (FEA) was used to assess the lever mechanics of the springhare masticatory system, and to determine the function of the IOZM. An FE model of the skull of P. capensis was constructed and loaded with all masticatory muscles, and then solved for biting at each tooth in turn. Further load cases were created in which each masticatory muscle was removed in turn. The analyses showed that the mechanical advantage of the springhare jaws was above one at all molar bites and very close to one during the premolar bite. Removing the IOZM or masseter caused a drop in mechanical advantage at all bites, but affected strain patterns and cranial deformation very little. Removing the ZM had only a small effect on mechanical advantage, but produced a substantial reduction in strain and deformation across the skull. It was concluded that the masticatory system of P. capensis acts as a second class lever during bites along almost the entire cheek tooth row. The IOZM is clearly a major contributor to this effect, but the masseter also has a part to play. The benefit of the IOZM is that it adds force without substantially contributing to strain or deformation of the skull. This may help explain why the hystricomorphous morphology has evolved multiple times independently within Rodentia.",
keywords = "Biomechanics, Finite element analysis, Hystricomorphy, Masticatory muscles, Pedetes capensis, Rodentia, Skull",
author = "Cox, {Philip Graham}",
note = "{\textcopyright} Philip Cox, 2017",
year = "2017",
month = aug,
day = "30",
doi = "10.7717/peerj.3741",
language = "English",
volume = "5",
pages = "e3741",
journal = "PeerJ",
issn = "2167-8359",
publisher = "PeerJ",
number = "8",

}

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TY - JOUR

T1 - The jaw is a second-class lever in Pedetes capensis (Rodentia: Pedetidae)

AU - Cox, Philip Graham

N1 - © Philip Cox, 2017

PY - 2017/8/30

Y1 - 2017/8/30

N2 - The mammalian jaw is often modelled as a third-class lever for the purposes of biomechanical analyses, owing to the position of the resultant muscle force between the jaw joint and the teeth. However, it has been proposed that in some rodents the jaws operate as a second-class lever during distal molar bites, owing to the rostral position of the masticatory musculature. In particular, the infraorbital portion of the zygomatico-mandibularis (IOZM) has been suggested to be of major importance in converting the masticatory system from a third-class to a second-class lever. The presence of the IOZM is diagnostic of the hystricomorph rodents, and is particularly well-developed in Pedetes capensis, the South African springhare. In this study, finite element analysis (FEA) was used to assess the lever mechanics of the springhare masticatory system, and to determine the function of the IOZM. An FE model of the skull of P. capensis was constructed and loaded with all masticatory muscles, and then solved for biting at each tooth in turn. Further load cases were created in which each masticatory muscle was removed in turn. The analyses showed that the mechanical advantage of the springhare jaws was above one at all molar bites and very close to one during the premolar bite. Removing the IOZM or masseter caused a drop in mechanical advantage at all bites, but affected strain patterns and cranial deformation very little. Removing the ZM had only a small effect on mechanical advantage, but produced a substantial reduction in strain and deformation across the skull. It was concluded that the masticatory system of P. capensis acts as a second class lever during bites along almost the entire cheek tooth row. The IOZM is clearly a major contributor to this effect, but the masseter also has a part to play. The benefit of the IOZM is that it adds force without substantially contributing to strain or deformation of the skull. This may help explain why the hystricomorphous morphology has evolved multiple times independently within Rodentia.

AB - The mammalian jaw is often modelled as a third-class lever for the purposes of biomechanical analyses, owing to the position of the resultant muscle force between the jaw joint and the teeth. However, it has been proposed that in some rodents the jaws operate as a second-class lever during distal molar bites, owing to the rostral position of the masticatory musculature. In particular, the infraorbital portion of the zygomatico-mandibularis (IOZM) has been suggested to be of major importance in converting the masticatory system from a third-class to a second-class lever. The presence of the IOZM is diagnostic of the hystricomorph rodents, and is particularly well-developed in Pedetes capensis, the South African springhare. In this study, finite element analysis (FEA) was used to assess the lever mechanics of the springhare masticatory system, and to determine the function of the IOZM. An FE model of the skull of P. capensis was constructed and loaded with all masticatory muscles, and then solved for biting at each tooth in turn. Further load cases were created in which each masticatory muscle was removed in turn. The analyses showed that the mechanical advantage of the springhare jaws was above one at all molar bites and very close to one during the premolar bite. Removing the IOZM or masseter caused a drop in mechanical advantage at all bites, but affected strain patterns and cranial deformation very little. Removing the ZM had only a small effect on mechanical advantage, but produced a substantial reduction in strain and deformation across the skull. It was concluded that the masticatory system of P. capensis acts as a second class lever during bites along almost the entire cheek tooth row. The IOZM is clearly a major contributor to this effect, but the masseter also has a part to play. The benefit of the IOZM is that it adds force without substantially contributing to strain or deformation of the skull. This may help explain why the hystricomorphous morphology has evolved multiple times independently within Rodentia.

KW - Biomechanics

KW - Finite element analysis

KW - Hystricomorphy

KW - Masticatory muscles

KW - Pedetes capensis

KW - Rodentia

KW - Skull

UR - http://www.scopus.com/inward/record.url?scp=85028524999&partnerID=8YFLogxK

U2 - 10.7717/peerj.3741

DO - 10.7717/peerj.3741

M3 - Article

VL - 5

SP - e3741

JO - PeerJ

JF - PeerJ

SN - 2167-8359

IS - 8

M1 - 3741

ER -