Book contents
- Frontmatter
- Contents
- List of contributors
- Foreword
- 1 Rodentia: a model order?
- 2 A synopsis of rodent molecular phylogenetics, systematics and biogeography
- 3 Emerging perspectives on some Paleogene sciurognath rodents in Laurasia: the fossil record and its interpretation
- 4 Phylogeny and evolutionary history of hystricognathous rodents from the Old World during the Tertiary: new insights into the emergence of modern “phiomorph” families
- 5 The history of South American octodontoid rodents and its contribution to evolutionary generalisations
- 6 History, taxonomy and palaeobiology of giant fossil rodents (Hystricognathi, Dinomyidae)
- 7 Advances in integrative taxonomy and evolution of African murid rodents: how morphological trees hide the molecular forest
- 8 Themes and variation in sciurid evolution
- 9 Marmot evolution and global change in the past 10 million years
- 10 Grades and clades among rodents: the promise of geometric morphometrics
- 11 Biogeographic variations in wood mice: testing for the role of morphological variation as a line of least resistance to evolution
- 12 The oral apparatus of rodents: variations on the theme of a gnawing machine
- 13 The muscles of mastication in rodents and the function of the medial pterygoid
- 14 Functional morphology of rodent middle ears
- 15 Variations and anomalies in rodent teeth and their importance for testing computational models of development
- 16 The great variety of dental structures and dynamics in rodents: new insights into their ecological diversity
- 17 Convergent evolution of molar topography in Muroidea (Rodentia, Mammalia): connections between chewing movements and crown morphology
- 18 Developmental mechanisms in the evolution of phenotypic traits in rodent teeth
- 19 Diversity and evolution of femoral variation in Ctenohystrica
- 20 Morphological disparity of the postcranial skeleton in rodents and its implications for palaeobiological inferences: the case of the extinct Theridomyidae (Rodentia, Mammalia)
- Index
- References
13 - The muscles of mastication in rodents and the function of the medial pterygoid
Published online by Cambridge University Press: 05 August 2015
Book contents
- Frontmatter
- Contents
- List of contributors
- Foreword
- 1 Rodentia: a model order?
- 2 A synopsis of rodent molecular phylogenetics, systematics and biogeography
- 3 Emerging perspectives on some Paleogene sciurognath rodents in Laurasia: the fossil record and its interpretation
- 4 Phylogeny and evolutionary history of hystricognathous rodents from the Old World during the Tertiary: new insights into the emergence of modern “phiomorph” families
- 5 The history of South American octodontoid rodents and its contribution to evolutionary generalisations
- 6 History, taxonomy and palaeobiology of giant fossil rodents (Hystricognathi, Dinomyidae)
- 7 Advances in integrative taxonomy and evolution of African murid rodents: how morphological trees hide the molecular forest
- 8 Themes and variation in sciurid evolution
- 9 Marmot evolution and global change in the past 10 million years
- 10 Grades and clades among rodents: the promise of geometric morphometrics
- 11 Biogeographic variations in wood mice: testing for the role of morphological variation as a line of least resistance to evolution
- 12 The oral apparatus of rodents: variations on the theme of a gnawing machine
- 13 The muscles of mastication in rodents and the function of the medial pterygoid
- 14 Functional morphology of rodent middle ears
- 15 Variations and anomalies in rodent teeth and their importance for testing computational models of development
- 16 The great variety of dental structures and dynamics in rodents: new insights into their ecological diversity
- 17 Convergent evolution of molar topography in Muroidea (Rodentia, Mammalia): connections between chewing movements and crown morphology
- 18 Developmental mechanisms in the evolution of phenotypic traits in rodent teeth
- 19 Diversity and evolution of femoral variation in Ctenohystrica
- 20 Morphological disparity of the postcranial skeleton in rodents and its implications for palaeobiological inferences: the case of the extinct Theridomyidae (Rodentia, Mammalia)
- Index
- References
Summary
Introduction
Mastication is a fundamental activity undertaken by mammals and the extent of oral food processing distinguishes them from other vertebrate groups. In order to break down food effectively, the mammals have evolved a complex set of masticatory muscles (Turnbull, 1970). Mammalian jaw-closing musculature comprises three distinct muscle groups: the temporalis, running from the temporal region of the skull posterior to the orbit to the coronoid process of the mandible; the masseter, which originates on the zygomatic arch and inserts on the ventrolateral surface of the mandibular ramus; and the pterygoid muscles, which run between the pterygoid region ventral to the orbit and the ventromedial surface of the mandible (Becht, 1953). The relative proportions of these muscles vary amongst mammals in a manner related to their diet and mode of feeding. Carnivores show an arrangement in which the temporalis is considerably larger than the masseter and pterygoids (Maynard Smith and Savage, 1959). Because the temporalis has a posterodorsal line of action and the squamosal is folded over the condyle to form a robust hinge, carnivores are able to produce powerful bite force at the teeth, whilst resisting the forward pull of struggling prey and thus maintaining the structural integrity of the jaw joint. In addition, the small, aborally positioned masseter muscle allows for a large gape and the ingestion of large food items (Becht, 1953). Conversely, herbivores display a configuration of enlarged masseter and pterygoid muscles and a reduced temporalis (Turnbull, 1970). The masseter extends further forward in herbivores and can thus work as a second-order lever and exert considerable masticatory pressure at the molar teeth (a clear advantage for grinding plant material). Furthermore, the complex, layered nature of the masseter and the open morphology of the temporo-mandibular joint allow mediolateral and anteroposterior movements of the mandible (Maynard Smith and Savage, 1959).
The masticatory musculature of rodents represents an extreme version of the herbivore configuration described above. In many rodents, the temporalis has reduced in size and the masseter has become the overwhelmingly dominant muscle, comprising around 70% of the entire masticatory muscle mass (Turnbull, 1970; Cox and Jeffery, 2011).
- Type
- Chapter
- Information
- Evolution of the RodentsAdvances in Phylogeny, Functional Morphology and Development, pp. 350 - 372Publisher: Cambridge University PressPrint publication year: 2015
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