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Marc E H Jones - One of the best experts on this subject based on the ideXlab platform.

  • a review of tooth implantation among Rhynchocephalians lepidosauria
    Journal of Herpetology, 2017
    Co-Authors: Kelsey M Jenkins, Marc E H Jones, Tomas Zikmund, Alan Boyde, Juan D. Daza
    Abstract:

    Abstract Acrodont dental implantation is widely considered an important character for referring fossil material to Rhynchocephalia. Under its purest definition, acrodonty involves teeth being attached to the crest of the marginal bones without roots. A similar mode of tooth attachment is known in a variety of other reptile groups including some squamates and procolophonids. There is a lack of consensus on the definition of acrodont, how best to characterize tooth implantation, and the relationship between implantation and tooth replacement. Rhynchocephalians already are known to demonstrate variation in their mode of tooth attachment. Unambiguous acrodonty associated with little or no tooth replacement has been associated with Sphenodon, but it appears to have been the most widespread condition for much of the Mesozoic. A form of pleurodonty, where teeth are attached to the inside of the jaw bone with shallow roots, appears to be the plesiomorphic condition for both Lepidosauria and Rhynchocephalia. Jaws ...

  • Sesamoid bones in tuatara (Sphenodon punctatus) investigated with X-ray microtomography, and implications for sesamoid evolution in Lepidosauria.
    Journal of Morphology, 2016
    Co-Authors: Sophie Regnault, John R. Hutchinson, Marc E H Jones
    Abstract:

    : Sesamoids bones are small intra-tendinous (or ligamentous) ossifications found near joints and are often variable between individuals. Related bones, lunulae, are found within the menisci of certain joints. Several studies have described sesamoids and lunulae in lizards and their close relatives (Squamata) as potentially useful characters in phylogenetic analysis, but their status in the extant outgroup to Squamata, tuatara (Sphenodon), remains unclear. Sphenodon is the only living Rhynchocephalian, but museum specimens are valuable and difficult to replace. Here, we use non-destructive X-ray microtomography to investigate the distribution of sesamoids and lunulae in 19 Sphenodon specimens and trace the evolution of these bones in Lepidosauria (Rhynchocephalia + Squamata). We find adult Sphenodon to possess a sesamoid and lunula complement different from any known squamate, but also some variation within Sphenodon specimens. The penultimate phalangeal sesamoids and tibial lunula appear to mineralize prior to skeletal maturity, followed by mineralization of a sesamoid between metatarsal I and the astragalocalcaneum (MTI-AC), the palmar sesamoids, and tibiofemoral lunulae around attainment of skeletal maturity. The tibial patella, ulnar, and plantar sesamoids mineralize late in maturity or variably. Ancestral state reconstruction indicates that the ulnar patella and tibiofemoral lunulae are synapomophies of Squamata, and the palmar sesamoid, tibial patella, tibial lunula, and MTI-AC may be synapomorphies of Lepidosauria. J. Morphol. 278:62-72, 2017. ©© 2016 Wiley Periodicals,Inc.

  • Anatomy, morphology and evolution of the patella in squamate lizards and tuatara (Sphenodon punctatus)
    Journal of Anatomy, 2016
    Co-Authors: Sophie Regnault, Marc E H Jones, Andrew A. Pitsillides, John R. Hutchinson
    Abstract:

    The patella (kneecap) is the largest and best-known of the sesamoid bones, postulated to confer biomechanical advantages including increasing joint leverage and reinforcing the tendon against compression. It has evolved several times independently in amniotes, but despite apparently widespread occurrence in lizards, the patella remains poorly characterised in this group and is, as yet, completely undescribed in their nearest extant relative Sphenodon (Rhynchocephalia). Through radiography, osteological and fossil studies we examined patellar presence in diverse lizard and lepidosauromorph taxa, and using computed tomography, dissection and histology we investigated in greater depth the anatomy and morphology of the patella in 16 lizard species and 19 Sphenodon specimens. We have found the first unambiguous evidence of a mineralised patella in Sphenodon, which appears similar to the patella of lizards and shares several gross and microscopic anatomical features. Although there may be a common mature morphology, the squamate patella exhibits a great deal of variability in development (whether from a cartilage anlage or not, and in the number of mineralised centres) and composition (bone, mineralised cartilage or fibrotendinous tissue). Unlike in mammals and birds, the patella in certain lizards and Sphenodon appears to be a polymorphic trait. We have also explored the evolution of the patella through ancestral state reconstruction, finding that the patella is ancestral for lizards and possibly Lepidosauria as a whole. Clear evidence of the patella in Rhynchocephalian or stem lepidosaurian fossil taxa would clarify the evolutionary origin(s) of the patella, but due to the small size of this bone and the opportunity for degradation or loss we could not definitively conclude presence or absence in the fossils examined. The pattern of evolution in lepidosaurs is unclear but our data suggest that the emergence of this sesamoid may be related to the evolution of secondary ossification centres and/or changes in knee joint conformation, where enhancement of extensor muscle leverage would be more beneficial.

  • tooth and cranial disparity in the fossil relatives of sphenodon Rhynchocephalia dispute the persistent living fossil label
    Journal of Evolutionary Biology, 2012
    Co-Authors: Carlo Meloro, Marc E H Jones
    Abstract:

    The tuatara (Sphenodon punctatus) is the only living representative of Rhynchocephalia, a group of small vertebrates that originated about 250 million years ago. The tuatara has been referred to as a living fossil; however, the group to which it belongs included a much greater diversity of forms in the Mesozoic. We explore the morphological diversity of Rhynchocephalia and stem lepidosaur relatives (Sphenodon plus 13 fossil relatives) by employing a combination of geometric morphometrics and comparative methods. Geometric morphometrics is used to explore cranium size and shape at interspecific scale, while comparative methods are employed to test association between skull shape and size and tooth number after taking phylogeny into account. Two phylogenetic topologies have been considered to generate a phylomorphospace and quantify the phylogenetic signal in skull shape data, the ancestral state reconstruction as well as morphological disparity using disparity through time plots (DTT). Rhynchocephalia exhibit a significant phylogenetic signal in skull shape that compares well with that computed for other extinct vertebrate groups. A consistent form of allometry has little impact on skull shape evolution while the number of teeth significantly correlates with skull shape also after taking phylogeny into account. The ancestral state reconstruction demonstrates a dramatic shape difference between the skull of Sphenodon and its much larger Cretaceous relative Priosphenodon. Additionally, DTT demonstrates that skull shape disparity is higher between rather than within clades while the opposite applies to skull size and number of teeth. These results were not altered by the use of competing phylogenic hypotheses. Rhynchocephalia evolved as a morphologically diverse group with a dramatic radiation in the Late Triassic and Early Jurassic about 200 million years ago. Differences in size are not marked between species whereas changes in number of teeth are associated with co-ordinated shape changes in the skull to accommodate larger masticatory muscles. These results show that the tuatara is not the product of evolutionary stasis but that it represents the only survivor of a diverse Mesozoic radiation whose subsequent decline remains to be explained.

  • shearing mechanics and the influence of a flexible symphysis during oral food processing in sphenodon lepidosauria Rhynchocephalia
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2012
    Co-Authors: Marc E H Jones, Susan E Evans, Michael J. Fagan, Paul Ohiggins, Neil Curtis
    Abstract:

    The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil Rhynchocephalians suggests that it was once more widespread.

Susan E Evans - One of the best experts on this subject based on the ideXlab platform.

  • The Lepidosaurian Ear: Variations on a Theme
    Evolution of the Vertebrate Ear, 2016
    Co-Authors: Susan E Evans
    Abstract:

    Today, Lepidosauria encompasses more than 9,000 species of lizards, snakes, and amphisbaenians (Squamata), as well as the New Zealand Tuatara, Sphenodon (Rhynchocephalia). In many lizards, an efficient tympanic middle ear and an effective inner-ear compensatory mechanism permit acute hearing across a range of frequencies. Sphenodon lacks a tympanic membrane, but this is the result of secondary loss. Fossils of stem lepidosaurs and early Rhynchocephalians indicate that the ancestral lepidosaurian middle ear was tympanic, although the compensatory mechanism was probably rudimentary. Derived Rhynchocephalians like Sphenodon lost the tympanic ear, possibly in association with feeding specializations, whereas squamates improved it by developing a more efficient compensatory window. However, the timing of this change is uncertain as the earliest lizard fossils are uninformative in this respect. Lizards from the Early Cretaceous onward show the derived condition. Squamates are morphologically and ecologically diverse, and some specialized lifestyles have affected ear anatomy. Among extant squamates, the only obligate marine swimmers are sea snakes, but in the Cretaceous, mosasaurs dominated the marine niche. These aquatic lizards show a middle ear morphology analogous to that of extant marine turtles (bulla-like quadrate, expanded extrastapes, loss of the tympanum?). Loss of the tympanum also occurs in squamate burrowers but in conjunction with the possession of a robust stapes with an enlarged footplate and, frequently, reduction or modification of the compensatory mechanism. Ears of this type are found in the enigmatic Cretaceous Sineoamphisbaena and in amphisbaenians from the Eocene to the present day. Where known, the ears of early snakes more closely resemble those of burrowers than swimmers.

  • shearing mechanics and the influence of a flexible symphysis during oral food processing in sphenodon lepidosauria Rhynchocephalia
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2012
    Co-Authors: Marc E H Jones, Susan E Evans, Michael J. Fagan, Paul Ohiggins, N. Curtis
    Abstract:

    The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil Rhynchocephalians suggests that it was once more widespread. Anat Rec, 2012. © 2012 Wiley-Periodicals, Inc.

  • shearing mechanics and the influence of a flexible symphysis during oral food processing in sphenodon lepidosauria Rhynchocephalia
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2012
    Co-Authors: Marc E H Jones, Susan E Evans, Michael J. Fagan, Paul Ohiggins, Neil Curtis
    Abstract:

    The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil Rhynchocephalians suggests that it was once more widespread.

  • hard tissue anatomy of the cranial joints in sphenodon Rhynchocephalia sutures kinesis and skull mechanics
    Palaeontologia Electronica, 2011
    Co-Authors: Marc E H Jones, N. Curtis, Michael J. Fagan, Paul Ohiggins, Susan E Evans
    Abstract:

    The anatomy of the extant lepidosaur Sphenodon (New Zealand tuatara) has been extensively examined by palaeontologists and comparative anatomists because of its phylogenetic status as the only living member of the Rhynchocephalia. It is also of interest because of its sophisticated feeding apparatus and a prooral (anteriorly directed) mode of shearing used to rip food apart. However, despite several detailed descriptions of the skull, the three-dimensional relationship between individual bones of the skull has generally been ignored. Here we provide the first joint by joint description of the hard tissue anatomy for almost every cranial suture in the skull of Sphenodon. This survey shows that most joints involve either abutments (e.g., along the midline) or extensive overlaps (e.g., more peripheral areas) but there are others that are heavily interlocked (e.g., postorbital-postfrontal) or involve a notable amount of soft tissue (e.g., vomer-premaxilla). There is variation in facet surface texture (e.g., smooth, ridged, pitted) but extensive interdigitation is uncommon and generally restricted to one plane. The joints do not appear suited to promote the marked intracranial movement reported in lizards such as geckos. However, it is possible that the base of the premaxillae would have been able to pivot slightly when loaded or impacted by the lower jaw during shearing. The extensive overlapping joints probably serve to maximise the surface area available for soft tissues that can dissipate and redistribute stress while maintaining the rigidity of the skull. These joints are larger in adults which bite more forcefully and may feed on harder prey.

  • The Origin, Early History and Diversification of Lepidosauromorph Reptiles
    New Aspects of Mesozoic Biodiversity, 2010
    Co-Authors: Susan E Evans, Marc E H Jones
    Abstract:

    The reptilian group Lepidosauria diversified through the Mesozoic, survived the end-Cretaceous extinction relatively unscathed, and has more than 7,000 living species. Although originally constituted as a “waste-bin” for non-archosaurian diapsids, modern definitions limit Lepidosauria to its two constituent groups, Rhynchocephalia and Squamata, and their most recent common ancestor. To date, the earliest known lepidosaurs are from the Late Triassic (Carnian) of Europe and India, but their derived morphology provides indirect evidence of a longer, unrecorded, history. Rhynchocephalians and squamates probably diverged in the Early-Middle Triassic, and new material from the Early Triassic of Poland sheds some light on their common ancestor. The roots of Lepidosauria may extend into the Palaeozoic, but there are critical gaps in the fossil record.

Hans-dieter Sues - One of the best experts on this subject based on the ideXlab platform.

  • a new species of clevosaurus lepidosauria Rhynchocephalia from the upper triassic of rio grande do sul brazil
    Palaeontology, 2006
    Co-Authors: Jose F Bonaparte, Hans-dieter Sues
    Abstract:

    Abstract: Well-preserved cranial remains of a small sphen-odontian lepidosaur from the Upper Triassic Caturrita For-mation of Rio Grande do Sul, Brazil, are the first record ofthe genus Clevosaurus Swinton, 1939 from South America.They represent a new species, Clevosaurus brasiliensis, whichis distinguished by a very short antorbital region of the skull(corresponding to about 20 per cent of skull length) and thepresence of teeth in addition to two longitudinal rows on thepterygoid. C. brasiliensis most closely resembles C. bairdifrom the Lower Jurassic of Nova Scotia (Canada) andC. mcgilli from the Lower Jurassic of Yunnan (China). Thediscovery of Clevosaurus in the Upper Triassic of southernBrazil provides a significant range extension of this widelydistributed sphenodontian genus. Along with other recentfinds, it also suggests that there may have been less bioticprovincialism among terrestrial vertebrates during the LateTriassic than has previously been assumed. Key words: Sphenodontia, Clevosaurus, Brazil, Triassic,Caturrita Formation, palaeobiogeography.

  • Lepidosaurian remains from the Lower Cretaceous Kirkwood Formation of South Africa
    Journal of Vertebrate Paleontology, 1999
    Co-Authors: Callum F. Ross, Hans-dieter Sues, William J. De Klerk
    Abstract:

    ABSTRACT New lepidosaurian material is reported from the Lower Cretaceous (middle to upper Valanginian) Kirk-wood Formation, South Africa. The material includes fragmentary jaws of a new sphenodontian and a well-preserved squamate braincase. The braincase is attributable to Squamata based on its possession of a complete abducens canal, a vidian canal that is fully enclosed posterodorsally, a divided metotic fissure, laterally directed basisphenoid processes, and distally expanded paroccipital processes. The prominent anterodorsally directed alar process is a similarity shared with Scleroglossa and some Iguanidae, and the presence of an open fenestra “rotunda” excludes the specimen from the Chameleontidae. The long posterior process of the dentary behind the coronoid process and enlargement of the palatine toothrow support reference of the jaws to the Rhynchocephalia. The open Meckelian groove, the addition of teeth at the back of the jaw, and the possession of at least some degree of acrodonty confirm the...

  • first record of the early mesozoic sphenodontian clevosaurus lepidosauria Rhynchocephalia from the southern hemisphere
    Journal of Paleontology, 1995
    Co-Authors: Hans-dieter Sues, Robert R Reisz
    Abstract:

    An incomplete skull of a small sphenodontian lepidosaur from the upper part of the Stormberg Group of southern Africa is referable to Clevosaurus Swinton, 1939. It is most closely related to C. bairdi from the McCoy Brook Formation (Lower Jurassic) of Nova Scotia (Canada) and C. mcgilli from the Dark Red Beds of the Lower Lufeng Formation (Lower Jurassic) of Yunnan (China). The new specimen is important because it represents the first record of Clevosaurus from the Southern Hemisphere. Like many other taxa of Early Jurassic continental tetrapods (crocodylomorph archosaurs, dinosaurs, synapsids), Clevosaurus had an apparently Pangaean distribution.

  • a new sphenodontian lepidosauria Rhynchocephalia from the mccoy brook formation lower jurassic of nova scotia canada
    Journal of Vertebrate Paleontology, 1994
    Co-Authors: Hans-dieter Sues, Neil H Shubin, Paul E Olsen
    Abstract:

    ABSTRACT A new sphenodontian lepidosaur referable to Clevosaurus Swinton, 1939, C. bairdi, is described from the McCoy Brook Formation (Lower Jurassic: Hettangian) of Nova Scotia, Canada. It is most closely related to C. mcgilli Wu, 1994 from the Dark Red Beds of the Lower Lufeng Formation (Lower Jurassic) of Yunnan, China, and differs from the latter mainly in the absence of the hourglass-shaped constriction of the parietals, the shape of the suborbital fenestra, and in features of the marginal dentition. The new taxon is of considerable interest because it represents the first record of Clevosaurus from North America. Like many other early Mesozoic continental tetrapods, Clevosaurus had an apparently Pangaean geographic distribution.

Michael J. Fagan - One of the best experts on this subject based on the ideXlab platform.

  • shearing mechanics and the influence of a flexible symphysis during oral food processing in sphenodon lepidosauria Rhynchocephalia
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2012
    Co-Authors: Marc E H Jones, Susan E Evans, Michael J. Fagan, Paul Ohiggins, Neil Curtis
    Abstract:

    The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil Rhynchocephalians suggests that it was once more widespread.

  • shearing mechanics and the influence of a flexible symphysis during oral food processing in sphenodon lepidosauria Rhynchocephalia
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2012
    Co-Authors: Marc E H Jones, Susan E Evans, Michael J. Fagan, Paul Ohiggins, N. Curtis
    Abstract:

    The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil Rhynchocephalians suggests that it was once more widespread. Anat Rec, 2012. © 2012 Wiley-Periodicals, Inc.

  • hard tissue anatomy of the cranial joints in sphenodon Rhynchocephalia sutures kinesis and skull mechanics
    Palaeontologia Electronica, 2011
    Co-Authors: Marc E H Jones, N. Curtis, Michael J. Fagan, Paul Ohiggins, Susan E Evans
    Abstract:

    The anatomy of the extant lepidosaur Sphenodon (New Zealand tuatara) has been extensively examined by palaeontologists and comparative anatomists because of its phylogenetic status as the only living member of the Rhynchocephalia. It is also of interest because of its sophisticated feeding apparatus and a prooral (anteriorly directed) mode of shearing used to rip food apart. However, despite several detailed descriptions of the skull, the three-dimensional relationship between individual bones of the skull has generally been ignored. Here we provide the first joint by joint description of the hard tissue anatomy for almost every cranial suture in the skull of Sphenodon. This survey shows that most joints involve either abutments (e.g., along the midline) or extensive overlaps (e.g., more peripheral areas) but there are others that are heavily interlocked (e.g., postorbital-postfrontal) or involve a notable amount of soft tissue (e.g., vomer-premaxilla). There is variation in facet surface texture (e.g., smooth, ridged, pitted) but extensive interdigitation is uncommon and generally restricted to one plane. The joints do not appear suited to promote the marked intracranial movement reported in lizards such as geckos. However, it is possible that the base of the premaxillae would have been able to pivot slightly when loaded or impacted by the lower jaw during shearing. The extensive overlapping joints probably serve to maximise the surface area available for soft tissues that can dissipate and redistribute stress while maintaining the rigidity of the skull. These joints are larger in adults which bite more forcefully and may feed on harder prey.

  • predicting muscle activation patterns from motion and anatomy modelling the skull of sphenodon diapsida Rhynchocephalia
    Journal of the Royal Society Interface, 2010
    Co-Authors: N. Curtis, Marc E H Jones, Susan E Evans, Paul Ohiggins, Michael J. Fagan
    Abstract:

    The relationship between skull shape and the forces generated during feeding is currently under widespread scrutiny and increasingly involves the use of computer simulations such as finite element analysis. The computer models used to represent skulls are often based on computed tomography data and thus are structurally accurate; however, correctly representing muscular loading during food reduction remains a major problem. Here, we present a novel approach for predicting the forces and activation patterns of muscles and muscle groups based on their known anatomical orientation (line of action). The work was carried out for the lizard-like reptile Sphenodon (Rhynchocephalia) using a sophisticated computer-based model and multi-body dynamics analysis. The model suggests that specific muscle groups control specific motions, and that during certain times in the bite cycle some muscles are highly active whereas others are inactive. The predictions of muscle activity closely correspond to data previously recorded from live Sphenodon using electromyography. Apparent exceptions can be explained by variations in food resistance, food size, food position and lower jaw motions. This approach shows considerable promise in advancing detailed functional models of food acquisition and reduction, and for use in other musculoskeletal systems where no experimental determination of muscle activity is possible, such as in rare, endangered or extinct species.

  • VISUALISING MUSCLE ANATOMY USING THREE-DIMENSIONAL COMPUTER MODELS - AN EXAMPLE USING THE HEAD AND NECK MUSCLES OF SPHENODON
    2009
    Co-Authors: N. Curtis, Marc E H Jones, Susan E Evans, Paul O'higgins, Michael J. Fagan
    Abstract:

    We demonstrate how the computer-based technique of multi-body dynamics analysis (MDA) can be used to create schematic, but informative three-dimensional (3D) representations of complex muscle anatomy. As an example we provide an overview of the head and neck muscles present in Sphenodon (Diapsida: Lepidosauria: Rhynchocephalia). First a computer model based on micro-computed tomography datasets provides a detailed and anatomically correct three-dimensional (3D) framework to work from. Secondly, muscles are represented by groups of cylinders that can be colour coded as desired. This allows muscle positions, attachment areas, and 3D orientation to be visualised clearly. This method has advantages over imaging techniques such as two-dimensional drawings and permits the form and function of the muscles to be understood in a way that is not always possible with more classical visualisation techniques. Copyright: Palaeontological Association December 2009.

N. Curtis - One of the best experts on this subject based on the ideXlab platform.

  • shearing mechanics and the influence of a flexible symphysis during oral food processing in sphenodon lepidosauria Rhynchocephalia
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2012
    Co-Authors: Marc E H Jones, Susan E Evans, Michael J. Fagan, Paul Ohiggins, N. Curtis
    Abstract:

    The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil Rhynchocephalians suggests that it was once more widespread. Anat Rec, 2012. © 2012 Wiley-Periodicals, Inc.

  • hard tissue anatomy of the cranial joints in sphenodon Rhynchocephalia sutures kinesis and skull mechanics
    Palaeontologia Electronica, 2011
    Co-Authors: Marc E H Jones, N. Curtis, Michael J. Fagan, Paul Ohiggins, Susan E Evans
    Abstract:

    The anatomy of the extant lepidosaur Sphenodon (New Zealand tuatara) has been extensively examined by palaeontologists and comparative anatomists because of its phylogenetic status as the only living member of the Rhynchocephalia. It is also of interest because of its sophisticated feeding apparatus and a prooral (anteriorly directed) mode of shearing used to rip food apart. However, despite several detailed descriptions of the skull, the three-dimensional relationship between individual bones of the skull has generally been ignored. Here we provide the first joint by joint description of the hard tissue anatomy for almost every cranial suture in the skull of Sphenodon. This survey shows that most joints involve either abutments (e.g., along the midline) or extensive overlaps (e.g., more peripheral areas) but there are others that are heavily interlocked (e.g., postorbital-postfrontal) or involve a notable amount of soft tissue (e.g., vomer-premaxilla). There is variation in facet surface texture (e.g., smooth, ridged, pitted) but extensive interdigitation is uncommon and generally restricted to one plane. The joints do not appear suited to promote the marked intracranial movement reported in lizards such as geckos. However, it is possible that the base of the premaxillae would have been able to pivot slightly when loaded or impacted by the lower jaw during shearing. The extensive overlapping joints probably serve to maximise the surface area available for soft tissues that can dissipate and redistribute stress while maintaining the rigidity of the skull. These joints are larger in adults which bite more forcefully and may feed on harder prey.

  • predicting muscle activation patterns from motion and anatomy modelling the skull of sphenodon diapsida Rhynchocephalia
    Journal of the Royal Society Interface, 2010
    Co-Authors: N. Curtis, Marc E H Jones, Susan E Evans, Paul Ohiggins, Michael J. Fagan
    Abstract:

    The relationship between skull shape and the forces generated during feeding is currently under widespread scrutiny and increasingly involves the use of computer simulations such as finite element analysis. The computer models used to represent skulls are often based on computed tomography data and thus are structurally accurate; however, correctly representing muscular loading during food reduction remains a major problem. Here, we present a novel approach for predicting the forces and activation patterns of muscles and muscle groups based on their known anatomical orientation (line of action). The work was carried out for the lizard-like reptile Sphenodon (Rhynchocephalia) using a sophisticated computer-based model and multi-body dynamics analysis. The model suggests that specific muscle groups control specific motions, and that during certain times in the bite cycle some muscles are highly active whereas others are inactive. The predictions of muscle activity closely correspond to data previously recorded from live Sphenodon using electromyography. Apparent exceptions can be explained by variations in food resistance, food size, food position and lower jaw motions. This approach shows considerable promise in advancing detailed functional models of food acquisition and reduction, and for use in other musculoskeletal systems where no experimental determination of muscle activity is possible, such as in rare, endangered or extinct species.

  • VISUALISING MUSCLE ANATOMY USING THREE-DIMENSIONAL COMPUTER MODELS - AN EXAMPLE USING THE HEAD AND NECK MUSCLES OF SPHENODON
    2009
    Co-Authors: N. Curtis, Marc E H Jones, Susan E Evans, Paul O'higgins, Michael J. Fagan
    Abstract:

    We demonstrate how the computer-based technique of multi-body dynamics analysis (MDA) can be used to create schematic, but informative three-dimensional (3D) representations of complex muscle anatomy. As an example we provide an overview of the head and neck muscles present in Sphenodon (Diapsida: Lepidosauria: Rhynchocephalia). First a computer model based on micro-computed tomography datasets provides a detailed and anatomically correct three-dimensional (3D) framework to work from. Secondly, muscles are represented by groups of cylinders that can be colour coded as desired. This allows muscle positions, attachment areas, and 3D orientation to be visualised clearly. This method has advantages over imaging techniques such as two-dimensional drawings and permits the form and function of the muscles to be understood in a way that is not always possible with more classical visualisation techniques. Copyright: Palaeontological Association December 2009.

  • the head and neck muscles associated with feeding in sphenodon reptilia lepidosauria Rhynchocephalia
    Palaeontologia Electronica 12 (2) Article 12.2.7A. (2009), 2009
    Co-Authors: Marc E H Jones, N. Curtis, Michael J. Fagan, Paul Ohiggins, Susan E Evans
    Abstract:

    Feeding in Sphenodon, the tuatara of New Zealand, is of interest for several rea-sons. First, the modern animal is threatened by extinction, and some populations are in competition for food with Pacific rats. Second, Sphenodon demonstrates a feeding apparatus that is unique to living amniotes: an enlarged palatine tooth row, acrodont dentition, enlarged incisor-like teeth on the premaxilla, a posterior extension of the dentary and an elongate articular surtace that permits prooral shearing. Third, Spheno-don has a skull with two complete lateral temporal bars and is therefore structurally analogous to the configuration hypothesised for the ancestral diapsid reptile. Further-more, the fossil relatives of Sphenodon demonstrate considerable variation in terms of feeding apparatus and skull shape. Lastly, as Sphenodon is the only extant rhyn-chocephalian it represents a potentially useful reference taxon for both muscle recon-struction in extinct reptile taxa and determination of muscle homology in extant taxa. Here we provide an up-to-date consensus view of osteology and musculature in Sphenodon that is relevant to feeding. Discrepancies within previous descriptions are evaluated and synthesised with new observations. This paper displays the complex muscle arrangement using a range of different imaging techniques and a variety of different angles. This includes photographs, illustrations, schematic diagrams, and microcomputed tomography (micro-CT) slice images. © Palaeontological Association August 2009.