The biomechanical role of the chondrocranium and sutures in a lizard cranium

Jones, Marc E. H.; Gröning, Flora; Dutel, Hugo; Sharp, Alana C.; Fagan, Michael J.; Evans, SE

doi:10.1098/rsif.2017.0637

Cited by 29 publications

(44 citation statements)

References 77 publications

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“…The ossification of this region of the chondrocranium is highly variable between species and appears to have evolved several times independently. The variability in the ossification of this region may correlate with the distribution of bite force across the chondrocranium (Evans, 2008;Jones et al 2017). The internarial element is unique to Champsosaurus and is a diagnostic feature of the genus (Gao & Fox, 1998;Matsumoto et al 2013).…”

Section: Conservation Of the Braincase Among Amniotes And Its Implicamentioning

confidence: 99%

Computed tomography analysis of the cranium of Champsosaurus lindoei and implications for the choristoderan neomorphic ossification

et al. 2020

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Choristoderes are extinct neodiapsid reptiles that are well known for their unusual cranial anatomy, possessing an elongated snout and expanded temporal arches. Although choristodere skulls are well described externally, their internal anatomy remains unknown. An internal description was needed to shed light on peculiarities of the choristodere skull, such as paired gaps on the ventral surface of the skull that may pertain to the fenestra ovalis, and a putative neomorphic ossification in the lateral wall of the braincase. Our goals were: (i) to describe the cranial elements of Champsosaurus lindoei in three dimensions; (ii) to describe paired gaps on the ventral surface of the skull to determine if these are indeed the fenestrae ovales; (iii) to illustrate the morphology of the putative neomorphic bone; and (iv) to consider the possible developmental and functional origins of the neomorph. We examined the cranial anatomy of the choristodere Champsosaurus lindoei (CMN 8920) using high‐resolution micro‐computed tomography scanning. We found that the paired gaps on the ventral surface of the skull do pertain to the fenestrae ovales, an unusual arrangement that may be convergent with some plesiosaurs, some aistopods, and some urodeles. The implications of this morphology in Champsosaurus are unknown and will be the subject of future work. We found that the neomorphic bone is a distinct ossification, but is not part of the wall of the brain cavity or the auditory capsule. Variation in the developmental pathways of cranial bones in living amniotes was surveyed to determine how the neomorphic bone may have developed. We found that the chondrocranium and splanchnocranium show little to no variation across amniotes, and the neomorphic bone is therefore most likely to have developed from the dermatocranium; however, the stapes is a pre‐existing cranial element that is undescribed in choristoderes and may be homologous with the neomorphic bone. If the neomorphic bone is not homologous with the stapes, the neomorph likely developed from the dermatocranium through incomplete fusion of ossification centres from a pre‐existing bone, most likely the parietal. Based on the apparent morphology of the neomorph in Coeruleodraco, the neomorph was probably too small to play a significant structural role in the skull of early choristoderes and it may have arisen through non‐adaptive means. In neochoristoderes, such as Champsosaurus, the neomorph was likely recruited to support the expanded temporal arches.

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Section: Conservation Of the Braincase Among Amniotes And Its Implicamentioning

confidence: 99%

Computed tomography analysis of the cranium of Champsosaurus lindoei and implications for the choristoderan neomorphic ossification

et al. 2020

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“…In this context, it is worth noting that we do not have a clear understanding of the functional morphology of the chondrocranium, at least in amniotes, although recent advances have been made (Jones et al, 2017). The original function of the cartilaginous skull in vertebrates might have lain in the physical protection of the sensory organs and the brain during early development or also in adult stages (Kaucka & Adameyko, 2019;Kaucka et al, 2018;Kawasaki & Richtsmeier, 2017).…”

Section: Functional Morphologymentioning

confidence: 99%

Character definition and tempus optimum in comparative chondrocranial research

Werneburg

Yaryhin

2018

Acta Zoologica

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Here, we define a research program using primordial skull characters for broad scale phylogenetic comparisons, particularly for amniotes. There are many chondrocranium descriptions in the literature, encompassing many clades of vertebrates. The definition of a comparable “tempus optimum” for fully formed chondrocrania, as developed herein, will enable discrete character definition in the sense of phylogenetic systematics. The “tempus optimum” is a time period in which the nose region shows full chondrification and the basicranium has not yet changed in its anatomy by ossification processes. For studies on heterochrony, changes in the developmental timing through evolution, the available data in the literature are insufficient. Anatomical standardizations, traceable methodological approaches and clear definitions of comparable developmental stages are needed. Moreover, for profound homology assertions of chondrocranial structures, ontogeny needs to be traced from early mesenchymal condensation, through several stages of cartilage development, up to postnatal stages, in which ossifications are already present. A holistic observation, including hard and soft tissue anatomy, is of paramount importance to generate hypotheses of homology with much explanatory power and to derive conclusions on functional morphology. For that, traditional histological methodology is needed. We exemplify the suggested approach in two case studies on the disputed laterosphenoid in turtles and crocodiles and on the homology of pila antotica in a pleurodire turtle, and, using here defined criteria, we formulate hypotheses on their homology.

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“…Soons et al, 2010;Santana and Dumont, 2011;McCurry et al, 2015), and the effects of soft tissue on non-mobile cranial joints (e.g. Curtis et al, 2013;Jones et al, 2017), and to create artificial morphologies (e.g. Moazen et al, 2009) and joint tissues to test different loading conditions.…”

Section: Introductionmentioning

confidence: 99%

The roles of joint tissues and jaw muscles in palatal biomechanics of the Savannah monitor (Varanus exanthematicus) and their significance for cranial kinesis

Wilken

Middleton

Sellers

et al. 2019

Journal of Experimental Biology

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Numerous vertebrates exhibit cranial kinesis, or movement between bones of the skull and mandible other than at the jaw joint. Many kinetic species possess a particular suite of features to accomplish this movement, including flexible cranial joints and protractor musculature. Whereas the musculoskeletal anatomy of these kinetic systems is well understood, how these joints are biomechanically loaded, how different soft tissues affect joint loading and kinetic capacity, and how the protractor musculature loads the skull remain poorly understood. Here, we present a finite element model of the savannah monitor, Varanus exanthematicus, a modestly kinetic lizard, to better elucidate the roles of soft tissue in mobile joints and protractor musculature in cranial loading. We describe the 3D resultants of jaw muscles and the histology of palatobasal, otic and jaw joints. We tested the effects of joint tissue type, bite point and muscle load to evaluate the biomechanical role of muscles on the palate and braincase. We found that the jaw muscles have significant mediolateral components that can impart stability across palatocranial joints. Articular tissues affect the magnitude of strains experienced around the palatobasal and otic joints. Without protractor muscle loading, the palate, quadrate and braincase experience higher strains, suggesting this muscle helps insulate the braincase and palatoquadrate from high loads. We found that the cross-sectional properties of the bones of V. exanthematicus are well suited for performing under torsional loads. These findings suggest that torsional loading regimes may have played a more important role in the evolution of cranial kinesis in lepidosaurs than previously appreciated.

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The biomechanical role of the chondrocranium and sutures in a lizard cranium

Cited by 29 publications

References 77 publications

Computed tomography analysis of the cranium of Champsosaurus lindoei and implications for the choristoderan neomorphic ossification

Computed tomography analysis of the cranium of Champsosaurus lindoei and implications for the choristoderan neomorphic ossification

Character definition and tempus optimum in comparative chondrocranial research

The roles of joint tissues and jaw muscles in palatal biomechanics of the Savannah monitor (Varanus exanthematicus) and their significance for cranial kinesis

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