Herein, we re-describe the holotype specimen of Youngina capensis using modern medical imaging te... more Herein, we re-describe the holotype specimen of Youngina capensis using modern medical imaging techniques. This area of the skull had never been described from complete specimens for this iconic early reptile. Our work offers the first 3D imaging of the braincase and the balance organs (vestibular system). Not only is this a new leap for Youngina but also among Permian early diapsid reptiles as a whole, for which often the deeper anatomy of the skull has not been well known.
Abstract The mechanical behavior of mammalian mandibles is well-studied, but a comprehensive biom... more Abstract The mechanical behavior of mammalian mandibles is well-studied, but a comprehensive biomechanical analysis (incorporating detailed muscle architecture, accurate material properties, and three-dimensional mechanical behavior) of an extant archosaur mandible has never been carried out. This makes it unclear how closely models of extant and extinct archosaur mandibles reflect reality and prevents comparisons of structure–function relationships in mammalian and archosaur mandibles.
Bone is a dynamic tissue with diverse functions including growth, structural support, pH balance ... more Bone is a dynamic tissue with diverse functions including growth, structural support, pH balance and reproduction. These functions may be compromised in the presence of organopollutants that can alter bone properties.
The cartilago transiliens is a fibrocartilaginous structure within the jaw muscles of crocodylian... more The cartilago transiliens is a fibrocartilaginous structure within the jaw muscles of crocodylians. The cartilago transiliens slides between the pterygoid buttress and coronoid region of the lower jaw and connects two muscles historically identified as m. pseudotemporalis superficialis and m. intramandibularis. However, the position of cartilago transiliens, and its anatomical similarities to tendon organs suggest the structure may be a sesamoid linking a single muscle.
Crocodyliforms were one of the most successful groups of Mesozoic tetrapods, radiating into terre... more Crocodyliforms were one of the most successful groups of Mesozoic tetrapods, radiating into terrestrial, semiaquatic and marine environments, while occupying numerous trophic niches, including carnivorous, insectivorous, herbivorous, and piscivorous species. Among these taxa were the enigmatic, poorly represented flat-headed crocodyliforms from the late Cretaceous of northern Africa. Here we report a new, giant crocodyliform from the early Late Cretaceous (Cenomanian) Kem Kem Formation of Morocco.
Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively simply shaped condylar... more Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively simply shaped condylar regions in their appendicular bones, suggesting potentially large amounts of unpreserved epiphyseal (articular) cartilage. This “lost anatomy” is often underappreciated such that the ends of bones are typically considered to be the joint surfaces, potentially having a major impact on functional interpretation.
SUMMARY Minke whales (Balaenoptera acutorostrata) are the smallest member of balaenopterid whales... more SUMMARY Minke whales (Balaenoptera acutorostrata) are the smallest member of balaenopterid whales and little is known of their kinematics during feeding maneuvers. These whales have narrow and elongated flippers that are small relative to body size compared to related species such as right and gray whales. No experimental studies have addressed the hydrodynamic properties of minke whale flippers and their functional role during feeding maneuvers.
Abstract Cranial kinesis is a widespread feature of gekkotan lizards. Previous studies of kinesis... more Abstract Cranial kinesis is a widespread feature of gekkotan lizards. Previous studies of kinesis in lizards often described the relevant, mobile joints as synovial, thus characterized by the presence of a synovial cavity lined with articular cartilage. To date however, detailed investigations of cranial joint histology are lacking.
Abstract Although the mandibular symphysis is a functionally and evolutionarily important feature... more Abstract Although the mandibular symphysis is a functionally and evolutionarily important feature of the vertebrate skull, little is known about the soft-tissue morphology of the joint in squamate reptiles. Lizards evolved a diversity of skull shapes and feeding behaviors, thus it is expected that the morphology of the symphysis will correspond with functional patterns. Here, we present new histological data illustrating the morphology of the joint in a number of taxa including iguanians, geckos, scincomorphs, lacertoids, and anguimorphs.
Abstract The functional effects of bone and suture stiffness were considered here using finite el... more Abstract The functional effects of bone and suture stiffness were considered here using finite element models representing three different theoretical phenotypes of an Alligator mississippiensis mandible. The models were loaded using force estimates derived from muscle architecture in dissected specimens, constrained at the 18th and 19th teeth in the upper jaw and 19th tooth of the lower jaw, as well as at the quadrate-articular joint. Stiffness was varied systematically in each theoretical phenotype.
Abstract Sauropod dinosaurs were the largest terrestrial herbivores and pushed at the limits of v... more Abstract Sauropod dinosaurs were the largest terrestrial herbivores and pushed at the limits of vertebrate biomechanics and physiology. Sauropods exhibit high craniodental diversity in ecosystems where numerous species co-existed, leading to the hypothesis that this biodiversity is linked to niche subdivision driven by ecological specialisation. Here, we quantitatively investigate feeding behaviour hypotheses for the iconic sauropod Diplodocus.
A broad survey of crocodyliform archosaurs and their outgroups was conducted to explore the evolu... more A broad survey of crocodyliform archosaurs and their outgroups was conducted to explore the evolutionary and morphological patterns of the orbitotemporal region, which is a highly apomorphic but poorly understood portion of the head. Data were gathered on the topological similarity and phylogenetic congruence of the epipterygoid, laterosphenoid, and temporal region as a whole, including relevant osteological correlates and such inferred soft tissues as the trigeminal nerves and jaw musculature. Despite the complete suturing of the palatocranial junction, the epipterygoid remained a consistent cranial element throughout crocodyliform evolution, only to be replaced by the topologically analogous, but developmentally neomorphic lateral bridge of the laterosphenoid during the early evolution of eusuchians. These changes led to a unique morphology of the region surrounding the exit of the trigeminal nerve. Mesoeucrocodylian taxa exhibit a diversity of epipterygoid morphologies including waisted (e.g., Araripesuchus), overlapping (e.g., Sarcosuchus), and isolated (e.g., Goniopholis, Leidyosuchus) forms. The isolated form, in which the epipterygoid is uncoupled from the pterygoid and does not to cover the cavum epiptericum laterally, represents a key transition to the extant condition of loss of the epipterygoid. Changes in the epipterygoid coincide with the migration of M. pseudotemporalis superficialis onto the laterosphenoid outside of the dorsotemporal fossa and the topological change in the intermuscular path of the maxillary nerve, both of which are apomorphies found in extant crocodylians. These data reflect a diverse and potentially homoplastic distribution of orbitotemporal morphologies among mesoeucrocodylians and indicate that the epipterygoid was only recently eliminated in crocodyliform evolution.
Jaw muscles are key components of the head and critical to testing hypotheses of soft-tissue homo... more Jaw muscles are key components of the head and critical to testing hypotheses of soft-tissue homology, skull function, and evolution. Dinosaurs evolved an extraordinary diversity of cranial forms adapted to a variety of feeding behaviors. However, disparate evolutionary transformations in head shape and function among dinosaurs and their living relatives, birds and crocodylians, impair straightforward reconstructions of muscles, and other important cephalic soft tissues. This study presents the osteological correlates and inferred soft tissue anatomy of the jaw muscles and relevant neurovasculature in the temporal region of the dinosaur head. Hypotheses of jaw muscle homology were tested across a broad range archosaur and sauropsid taxa to more accurately infer muscle attachments in the adductor chambers of nonavian dinosaurs. Many dinosaurs likely possessed m. levator pterygoideus, a trait shared with lepidosaurs but not extant archosaurs. Several major clades of dinosaurs (e.g., Ornithopoda, Ceratopsidae, Sauropoda) eliminated the epipterygoid, thus impacting interpretations of m. pseudotemporalis profundus. M. pseudotemporalis superficialis most likely attached to the caudoventral surface of the laterosphenoid, a trait shared with extant archosaurs. Although mm. adductor mandibulae externus profundus and medialis likely attached to the caudal half of the dorsotemporal fossa and coronoid process, clear osteological correlates separating the individual bellies are rare. Most dinosaur clades possess osteological correlates indicative of a pterygoideus ventralis muscle that attaches to the lateral surface of the mandible, although the muscle may have extended as far as the jugal in some taxa (e.g., hadrosaurs, tyrannosaurs). The cranial and mandibular attachments of mm adductor mandibulae externus superficialis and adductor mandibulae posterior were consistent across all taxa studied. These new data greatly increase the interpretive resolution of head anatomy in dinosaurs and provide the anatomical foundation necessary for future analyses of skull function and evolution in an important vertebrate clade. Anat Rec, 292:1246–1265, 2009. VVC 2009 Wiley-Liss, Inc.
Different forms of intracranial mobility, including streptostyly, pleurokinesis, and prokinesis, ... more Different forms of intracranial mobility, including streptostyly, pleurokinesis, and prokinesis, have been postulated for many dinosaurs. The basis for inferring kinesis typically has included the presence of presumably synovial intracranial joints (otic and basal joints) and various ad hoc ‘sliding joints’ (many without modern parallels), whereas the protractor musculature that would have powered movement at these joints has received little attention. No study has reviewed the evidence underlying these inferences, and the functional mechanisms and evolution of kinesis among dinosaurs have remained unclear. We analyzed the relevant musculoskeletal structures in extant diapsids and extinct dinosaurs to evaluate in general the morphological support for inferences of cranial kinesis in dinosaurs. Four criteria (synovial otic joints, synovial basal joints, protractor muscles, and permissive kinematic linkages) were considered necessary but individually insufficient for the inference of kinesis. Assessing these criteria across dinosaurs reveals that synovial otic and basal joints are almost universally present (even in widely acknowledged akinetic taxa), and most taxa retained protractor musculature. However, unlike fully kinetic extant birds and squamates, almost all dinosaurs lacked the kinematic linkages that would have permitted movement (reduced palatal and temporal articulations, additional flexion zones). Thus, synovial basal and otic joints and protractor musculature are diapsid plesiomorphies, and, in the absence of permissive kinematic linkages, most formulations of nonavian dinosaur kinesis are currently problematic. Alternatively, persistent synovial joints may simply be cartilaginous sites that facilitate cranial growth during ontogeny.
Here we describe a 3-D animated model of the craniodental system of a hadrosaur, developed for te... more Here we describe a 3-D animated model of the craniodental system of a hadrosaur, developed for testing hypotheses of feeding kinematics. The model was created from scanned cranial elements of an Edmontosaurus regalis paratype (CMN 2289). Movements within the model were created in animation software using inverse kinematics and a wiring system composed of cranial elements. The model was used toreproduce the pleurokinetic hypothesis of hadrosaur chewing. The pleurokinetic hypothesis, formally developed in the 1980s, proposed that hadrosaurs employed transverse chewing movements via cranial kinesis. Specifically during the powerstroke the maxillae were abducted. This is the first model to allow investigation into secondary intracranial movements that must have occurred in order for the skull to accommodate the primary, pleurokinetic movements. This study found secondary movements to be extensive among the joints of the palate and face. Further refinement and developmentof the model, including the integration of soft-tissue structures, will allow for a morein-depth examination of the pleurokinetic hypothesis and comparison with alternative feeding hypotheses.
The homologies of jaw muscles among archosaurs and other sauropsids have been unclear, confoundin... more The homologies of jaw muscles among archosaurs and other sauropsids have been unclear, confounding interpretation of adductor chamber morphology and evolution. Relevant topological patterns of muscles, nerves, and blood vessels were compared across a large sample of extant archosaurs (birds and crocodylians) and outgroups (e.g., lepidosaurs and turtles) to test the utility of positional criteria, such as the relative position of the trigeminal divisions, as predictors of jaw muscle homology. Anatomical structures were visualized using dissection, sectioning, computed tomography (CT), and vascular injection. Data gathered provide a new and robust view of jaw muscle homology and introduce the first synthesized nomenclature of sauropsid musculature using multiple lines of evidence. Despite the great divergences in cephalic morphology among birds, crocodylians, and outgroups, several key sensory nerves (e.g., n. anguli oris, n. supraorbitalis, n. caudalis) and arteries proved useful for muscle identification, and vice versa. Extant crocodylians exhibit an apomorphic neuromuscular pattern counter to the trigeminal topological paradigm: the maxillary nerve runs medial, rather than lateral to M. pseudotemporalis superficialis. Alternative hypotheses of homology necessitate less parsimonious interpretations of changes in topology. Sensory branches to the rictus, external acoustic meatus, supraorbital region, and other cephalic regions suggest conservative dermatomes among reptiles. Different avian clades exhibit shifts in some muscle positions, but maintain the plesiomorphic, diapsid soft-tissue topological pattern. Positional data suggest M. intramandibularis is merely the distal portion of M. pseudotemporalis separated by an intramuscular fibrocartilaginous sesamoid. These adductor chamber patterns indicate multiple topological criteria are necessary for interpretations of soft-tissue homology and warrant further investigation into character congruence and developmental connectivity.
Head vascular anatomy of the greater (or Caribbean) flamingo (Phoenicopterus ruber) is investigat... more Head vascular anatomy of the greater (or Caribbean) flamingo (Phoenicopterus ruber) is investigated and illustrated through the use of a differential contrast, dual vascular injection technique, and high-resolution X-ray computed tomography (CT), allowing arteries and veins to be differentiated radiographically. Vessels were digitally isolated with segmentationtools and reconstructed in 3D to facilitate topographical visualization of the cephalic vascular tree. Major vessels of the temporal, orbital, pharyngeal, and encephalic regions are described and illustrated, which confirm that the general pattern of avian cephalic vasculature is evolutionarily conservative. In addition to numerous arteriovenous vascular devices, a previously undescribed, large, bilateral, paralingual cavernous sinus that excavates a large bony fossa on the medial surface of the mandible was identified. Despite the otherwise conservative vascular pattern, this paralingual sinus was found only in species of flamingo and is not known otherwise in birds. The paralingual sinus remains functionally enigmatic, but a mechanical role in association with the peculiar lingual-pumping mode of feeding in flamingos is perhaps the most likely hypothesis.
Herein, we re-describe the holotype specimen of Youngina capensis using modern medical imaging te... more Herein, we re-describe the holotype specimen of Youngina capensis using modern medical imaging techniques. This area of the skull had never been described from complete specimens for this iconic early reptile. Our work offers the first 3D imaging of the braincase and the balance organs (vestibular system). Not only is this a new leap for Youngina but also among Permian early diapsid reptiles as a whole, for which often the deeper anatomy of the skull has not been well known.
Abstract The mechanical behavior of mammalian mandibles is well-studied, but a comprehensive biom... more Abstract The mechanical behavior of mammalian mandibles is well-studied, but a comprehensive biomechanical analysis (incorporating detailed muscle architecture, accurate material properties, and three-dimensional mechanical behavior) of an extant archosaur mandible has never been carried out. This makes it unclear how closely models of extant and extinct archosaur mandibles reflect reality and prevents comparisons of structure–function relationships in mammalian and archosaur mandibles.
Bone is a dynamic tissue with diverse functions including growth, structural support, pH balance ... more Bone is a dynamic tissue with diverse functions including growth, structural support, pH balance and reproduction. These functions may be compromised in the presence of organopollutants that can alter bone properties.
The cartilago transiliens is a fibrocartilaginous structure within the jaw muscles of crocodylian... more The cartilago transiliens is a fibrocartilaginous structure within the jaw muscles of crocodylians. The cartilago transiliens slides between the pterygoid buttress and coronoid region of the lower jaw and connects two muscles historically identified as m. pseudotemporalis superficialis and m. intramandibularis. However, the position of cartilago transiliens, and its anatomical similarities to tendon organs suggest the structure may be a sesamoid linking a single muscle.
Crocodyliforms were one of the most successful groups of Mesozoic tetrapods, radiating into terre... more Crocodyliforms were one of the most successful groups of Mesozoic tetrapods, radiating into terrestrial, semiaquatic and marine environments, while occupying numerous trophic niches, including carnivorous, insectivorous, herbivorous, and piscivorous species. Among these taxa were the enigmatic, poorly represented flat-headed crocodyliforms from the late Cretaceous of northern Africa. Here we report a new, giant crocodyliform from the early Late Cretaceous (Cenomanian) Kem Kem Formation of Morocco.
Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively simply shaped condylar... more Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively simply shaped condylar regions in their appendicular bones, suggesting potentially large amounts of unpreserved epiphyseal (articular) cartilage. This “lost anatomy” is often underappreciated such that the ends of bones are typically considered to be the joint surfaces, potentially having a major impact on functional interpretation.
SUMMARY Minke whales (Balaenoptera acutorostrata) are the smallest member of balaenopterid whales... more SUMMARY Minke whales (Balaenoptera acutorostrata) are the smallest member of balaenopterid whales and little is known of their kinematics during feeding maneuvers. These whales have narrow and elongated flippers that are small relative to body size compared to related species such as right and gray whales. No experimental studies have addressed the hydrodynamic properties of minke whale flippers and their functional role during feeding maneuvers.
Abstract Cranial kinesis is a widespread feature of gekkotan lizards. Previous studies of kinesis... more Abstract Cranial kinesis is a widespread feature of gekkotan lizards. Previous studies of kinesis in lizards often described the relevant, mobile joints as synovial, thus characterized by the presence of a synovial cavity lined with articular cartilage. To date however, detailed investigations of cranial joint histology are lacking.
Abstract Although the mandibular symphysis is a functionally and evolutionarily important feature... more Abstract Although the mandibular symphysis is a functionally and evolutionarily important feature of the vertebrate skull, little is known about the soft-tissue morphology of the joint in squamate reptiles. Lizards evolved a diversity of skull shapes and feeding behaviors, thus it is expected that the morphology of the symphysis will correspond with functional patterns. Here, we present new histological data illustrating the morphology of the joint in a number of taxa including iguanians, geckos, scincomorphs, lacertoids, and anguimorphs.
Abstract The functional effects of bone and suture stiffness were considered here using finite el... more Abstract The functional effects of bone and suture stiffness were considered here using finite element models representing three different theoretical phenotypes of an Alligator mississippiensis mandible. The models were loaded using force estimates derived from muscle architecture in dissected specimens, constrained at the 18th and 19th teeth in the upper jaw and 19th tooth of the lower jaw, as well as at the quadrate-articular joint. Stiffness was varied systematically in each theoretical phenotype.
Abstract Sauropod dinosaurs were the largest terrestrial herbivores and pushed at the limits of v... more Abstract Sauropod dinosaurs were the largest terrestrial herbivores and pushed at the limits of vertebrate biomechanics and physiology. Sauropods exhibit high craniodental diversity in ecosystems where numerous species co-existed, leading to the hypothesis that this biodiversity is linked to niche subdivision driven by ecological specialisation. Here, we quantitatively investigate feeding behaviour hypotheses for the iconic sauropod Diplodocus.
A broad survey of crocodyliform archosaurs and their outgroups was conducted to explore the evolu... more A broad survey of crocodyliform archosaurs and their outgroups was conducted to explore the evolutionary and morphological patterns of the orbitotemporal region, which is a highly apomorphic but poorly understood portion of the head. Data were gathered on the topological similarity and phylogenetic congruence of the epipterygoid, laterosphenoid, and temporal region as a whole, including relevant osteological correlates and such inferred soft tissues as the trigeminal nerves and jaw musculature. Despite the complete suturing of the palatocranial junction, the epipterygoid remained a consistent cranial element throughout crocodyliform evolution, only to be replaced by the topologically analogous, but developmentally neomorphic lateral bridge of the laterosphenoid during the early evolution of eusuchians. These changes led to a unique morphology of the region surrounding the exit of the trigeminal nerve. Mesoeucrocodylian taxa exhibit a diversity of epipterygoid morphologies including waisted (e.g., Araripesuchus), overlapping (e.g., Sarcosuchus), and isolated (e.g., Goniopholis, Leidyosuchus) forms. The isolated form, in which the epipterygoid is uncoupled from the pterygoid and does not to cover the cavum epiptericum laterally, represents a key transition to the extant condition of loss of the epipterygoid. Changes in the epipterygoid coincide with the migration of M. pseudotemporalis superficialis onto the laterosphenoid outside of the dorsotemporal fossa and the topological change in the intermuscular path of the maxillary nerve, both of which are apomorphies found in extant crocodylians. These data reflect a diverse and potentially homoplastic distribution of orbitotemporal morphologies among mesoeucrocodylians and indicate that the epipterygoid was only recently eliminated in crocodyliform evolution.
Jaw muscles are key components of the head and critical to testing hypotheses of soft-tissue homo... more Jaw muscles are key components of the head and critical to testing hypotheses of soft-tissue homology, skull function, and evolution. Dinosaurs evolved an extraordinary diversity of cranial forms adapted to a variety of feeding behaviors. However, disparate evolutionary transformations in head shape and function among dinosaurs and their living relatives, birds and crocodylians, impair straightforward reconstructions of muscles, and other important cephalic soft tissues. This study presents the osteological correlates and inferred soft tissue anatomy of the jaw muscles and relevant neurovasculature in the temporal region of the dinosaur head. Hypotheses of jaw muscle homology were tested across a broad range archosaur and sauropsid taxa to more accurately infer muscle attachments in the adductor chambers of nonavian dinosaurs. Many dinosaurs likely possessed m. levator pterygoideus, a trait shared with lepidosaurs but not extant archosaurs. Several major clades of dinosaurs (e.g., Ornithopoda, Ceratopsidae, Sauropoda) eliminated the epipterygoid, thus impacting interpretations of m. pseudotemporalis profundus. M. pseudotemporalis superficialis most likely attached to the caudoventral surface of the laterosphenoid, a trait shared with extant archosaurs. Although mm. adductor mandibulae externus profundus and medialis likely attached to the caudal half of the dorsotemporal fossa and coronoid process, clear osteological correlates separating the individual bellies are rare. Most dinosaur clades possess osteological correlates indicative of a pterygoideus ventralis muscle that attaches to the lateral surface of the mandible, although the muscle may have extended as far as the jugal in some taxa (e.g., hadrosaurs, tyrannosaurs). The cranial and mandibular attachments of mm adductor mandibulae externus superficialis and adductor mandibulae posterior were consistent across all taxa studied. These new data greatly increase the interpretive resolution of head anatomy in dinosaurs and provide the anatomical foundation necessary for future analyses of skull function and evolution in an important vertebrate clade. Anat Rec, 292:1246–1265, 2009. VVC 2009 Wiley-Liss, Inc.
Different forms of intracranial mobility, including streptostyly, pleurokinesis, and prokinesis, ... more Different forms of intracranial mobility, including streptostyly, pleurokinesis, and prokinesis, have been postulated for many dinosaurs. The basis for inferring kinesis typically has included the presence of presumably synovial intracranial joints (otic and basal joints) and various ad hoc ‘sliding joints’ (many without modern parallels), whereas the protractor musculature that would have powered movement at these joints has received little attention. No study has reviewed the evidence underlying these inferences, and the functional mechanisms and evolution of kinesis among dinosaurs have remained unclear. We analyzed the relevant musculoskeletal structures in extant diapsids and extinct dinosaurs to evaluate in general the morphological support for inferences of cranial kinesis in dinosaurs. Four criteria (synovial otic joints, synovial basal joints, protractor muscles, and permissive kinematic linkages) were considered necessary but individually insufficient for the inference of kinesis. Assessing these criteria across dinosaurs reveals that synovial otic and basal joints are almost universally present (even in widely acknowledged akinetic taxa), and most taxa retained protractor musculature. However, unlike fully kinetic extant birds and squamates, almost all dinosaurs lacked the kinematic linkages that would have permitted movement (reduced palatal and temporal articulations, additional flexion zones). Thus, synovial basal and otic joints and protractor musculature are diapsid plesiomorphies, and, in the absence of permissive kinematic linkages, most formulations of nonavian dinosaur kinesis are currently problematic. Alternatively, persistent synovial joints may simply be cartilaginous sites that facilitate cranial growth during ontogeny.
Here we describe a 3-D animated model of the craniodental system of a hadrosaur, developed for te... more Here we describe a 3-D animated model of the craniodental system of a hadrosaur, developed for testing hypotheses of feeding kinematics. The model was created from scanned cranial elements of an Edmontosaurus regalis paratype (CMN 2289). Movements within the model were created in animation software using inverse kinematics and a wiring system composed of cranial elements. The model was used toreproduce the pleurokinetic hypothesis of hadrosaur chewing. The pleurokinetic hypothesis, formally developed in the 1980s, proposed that hadrosaurs employed transverse chewing movements via cranial kinesis. Specifically during the powerstroke the maxillae were abducted. This is the first model to allow investigation into secondary intracranial movements that must have occurred in order for the skull to accommodate the primary, pleurokinetic movements. This study found secondary movements to be extensive among the joints of the palate and face. Further refinement and developmentof the model, including the integration of soft-tissue structures, will allow for a morein-depth examination of the pleurokinetic hypothesis and comparison with alternative feeding hypotheses.
The homologies of jaw muscles among archosaurs and other sauropsids have been unclear, confoundin... more The homologies of jaw muscles among archosaurs and other sauropsids have been unclear, confounding interpretation of adductor chamber morphology and evolution. Relevant topological patterns of muscles, nerves, and blood vessels were compared across a large sample of extant archosaurs (birds and crocodylians) and outgroups (e.g., lepidosaurs and turtles) to test the utility of positional criteria, such as the relative position of the trigeminal divisions, as predictors of jaw muscle homology. Anatomical structures were visualized using dissection, sectioning, computed tomography (CT), and vascular injection. Data gathered provide a new and robust view of jaw muscle homology and introduce the first synthesized nomenclature of sauropsid musculature using multiple lines of evidence. Despite the great divergences in cephalic morphology among birds, crocodylians, and outgroups, several key sensory nerves (e.g., n. anguli oris, n. supraorbitalis, n. caudalis) and arteries proved useful for muscle identification, and vice versa. Extant crocodylians exhibit an apomorphic neuromuscular pattern counter to the trigeminal topological paradigm: the maxillary nerve runs medial, rather than lateral to M. pseudotemporalis superficialis. Alternative hypotheses of homology necessitate less parsimonious interpretations of changes in topology. Sensory branches to the rictus, external acoustic meatus, supraorbital region, and other cephalic regions suggest conservative dermatomes among reptiles. Different avian clades exhibit shifts in some muscle positions, but maintain the plesiomorphic, diapsid soft-tissue topological pattern. Positional data suggest M. intramandibularis is merely the distal portion of M. pseudotemporalis separated by an intramuscular fibrocartilaginous sesamoid. These adductor chamber patterns indicate multiple topological criteria are necessary for interpretations of soft-tissue homology and warrant further investigation into character congruence and developmental connectivity.
Head vascular anatomy of the greater (or Caribbean) flamingo (Phoenicopterus ruber) is investigat... more Head vascular anatomy of the greater (or Caribbean) flamingo (Phoenicopterus ruber) is investigated and illustrated through the use of a differential contrast, dual vascular injection technique, and high-resolution X-ray computed tomography (CT), allowing arteries and veins to be differentiated radiographically. Vessels were digitally isolated with segmentationtools and reconstructed in 3D to facilitate topographical visualization of the cephalic vascular tree. Major vessels of the temporal, orbital, pharyngeal, and encephalic regions are described and illustrated, which confirm that the general pattern of avian cephalic vasculature is evolutionarily conservative. In addition to numerous arteriovenous vascular devices, a previously undescribed, large, bilateral, paralingual cavernous sinus that excavates a large bony fossa on the medial surface of the mandible was identified. Despite the otherwise conservative vascular pattern, this paralingual sinus was found only in species of flamingo and is not known otherwise in birds. The paralingual sinus remains functionally enigmatic, but a mechanical role in association with the peculiar lingual-pumping mode of feeding in flamingos is perhaps the most likely hypothesis.
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analogous, but developmentally neomorphic lateral bridge of the laterosphenoid during the early evolution of eusuchians. These changes led to a unique morphology of the region surrounding the exit of the trigeminal nerve. Mesoeucrocodylian taxa exhibit a diversity of epipterygoid morphologies including waisted (e.g., Araripesuchus), overlapping (e.g., Sarcosuchus), and isolated (e.g., Goniopholis, Leidyosuchus) forms. The isolated form, in which the epipterygoid is uncoupled from the pterygoid and does not to cover the cavum epiptericum laterally, represents a key transition to the extant condition of loss of the epipterygoid. Changes in the epipterygoid coincide with the migration of M. pseudotemporalis superficialis onto the laterosphenoid outside of the dorsotemporal fossa and the topological change in the intermuscular path of the maxillary nerve, both of which are apomorphies found in extant crocodylians. These data reflect a diverse and potentially homoplastic distribution of orbitotemporal morphologies among mesoeucrocodylians and indicate that the epipterygoid was only recently eliminated in crocodyliform evolution.
correlates separating the individual bellies are rare. Most dinosaur clades possess osteological correlates indicative of a pterygoideus ventralis muscle that attaches to the lateral surface of the mandible, although the muscle may have extended as far as the jugal in some taxa (e.g., hadrosaurs, tyrannosaurs). The cranial and mandibular attachments of mm adductor mandibulae externus superficialis and adductor mandibulae posterior were consistent across all taxa studied. These new data greatly increase the interpretive resolution of head anatomy in dinosaurs and provide the anatomical foundation necessary for future analyses of skull function and evolution in an important vertebrate clade. Anat Rec, 292:1246–1265, 2009. VVC 2009 Wiley-Liss, Inc.
and encephalic regions are described and illustrated, which confirm that the general pattern of avian cephalic vasculature is evolutionarily conservative. In addition to numerous arteriovenous vascular devices, a previously undescribed, large, bilateral, paralingual cavernous sinus that excavates a large bony fossa on the medial surface of the mandible was identified. Despite the otherwise conservative vascular pattern, this paralingual sinus was found only in species of flamingo and is not known otherwise in birds. The paralingual sinus remains functionally enigmatic, but a mechanical role in association with the peculiar lingual-pumping mode of feeding in flamingos is perhaps the most likely hypothesis.
analogous, but developmentally neomorphic lateral bridge of the laterosphenoid during the early evolution of eusuchians. These changes led to a unique morphology of the region surrounding the exit of the trigeminal nerve. Mesoeucrocodylian taxa exhibit a diversity of epipterygoid morphologies including waisted (e.g., Araripesuchus), overlapping (e.g., Sarcosuchus), and isolated (e.g., Goniopholis, Leidyosuchus) forms. The isolated form, in which the epipterygoid is uncoupled from the pterygoid and does not to cover the cavum epiptericum laterally, represents a key transition to the extant condition of loss of the epipterygoid. Changes in the epipterygoid coincide with the migration of M. pseudotemporalis superficialis onto the laterosphenoid outside of the dorsotemporal fossa and the topological change in the intermuscular path of the maxillary nerve, both of which are apomorphies found in extant crocodylians. These data reflect a diverse and potentially homoplastic distribution of orbitotemporal morphologies among mesoeucrocodylians and indicate that the epipterygoid was only recently eliminated in crocodyliform evolution.
correlates separating the individual bellies are rare. Most dinosaur clades possess osteological correlates indicative of a pterygoideus ventralis muscle that attaches to the lateral surface of the mandible, although the muscle may have extended as far as the jugal in some taxa (e.g., hadrosaurs, tyrannosaurs). The cranial and mandibular attachments of mm adductor mandibulae externus superficialis and adductor mandibulae posterior were consistent across all taxa studied. These new data greatly increase the interpretive resolution of head anatomy in dinosaurs and provide the anatomical foundation necessary for future analyses of skull function and evolution in an important vertebrate clade. Anat Rec, 292:1246–1265, 2009. VVC 2009 Wiley-Liss, Inc.
and encephalic regions are described and illustrated, which confirm that the general pattern of avian cephalic vasculature is evolutionarily conservative. In addition to numerous arteriovenous vascular devices, a previously undescribed, large, bilateral, paralingual cavernous sinus that excavates a large bony fossa on the medial surface of the mandible was identified. Despite the otherwise conservative vascular pattern, this paralingual sinus was found only in species of flamingo and is not known otherwise in birds. The paralingual sinus remains functionally enigmatic, but a mechanical role in association with the peculiar lingual-pumping mode of feeding in flamingos is perhaps the most likely hypothesis.