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Mechanical factors in the design of the skull of Tyrannosaurus rex (Osborn, 1905)

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... Because many of the joints linking the palate to the braincase remain unfused, the skulls of many extinct species of dinosaurs, crocodylomorphs, and other fossil reptiles have also been hypothesized to have had various forms of cranial kinesis (Rayfield, 2005a;Holliday and Witmer, 2007). For example, Tyrannosaurus rex, which has plesiomorphic, ball and socket-shaped palatobasal and otic joints, has been hypothesized by different authors to have possessed one of several forms of cranial kinesis (Molnar, 1998;Rayfield, 2004;Larsson, 2008). A functional paradox remains: why do mature individuals of one of the world's most forceful biting, osteophagus animals (Gignac and Erickson, 2017) ever known maintain flexible joints when the hardest biting taxa of other terrestrial lineages (e.g., crocodile, tiger, and hyena; Erickson et al., 2003;Wroe et al., 2005;Tseng and Binder, 2010) suture their cranial elements to form rigid skulls? ...
... Osborn (1912) first remarked on the seemingly mobile nature of particular condylar joints but suggested the surrounding bones limited any particular movement. Also citing the condylar otic joint between the quadrate and squamosal, Molnar (1991Molnar ( , 1998 instead inferred limited streptostyly (rotation of the quadrate about the otic joint) in Tyrannosaurus. Rayfield (2004Rayfield ( ), 2005a inferred numerous sutural and condylar joints within the palate and face of Allosaurus, Tyrannosaurus, and other theropods to be capable of movement following finite element analysis (FEA) of patterns of stresses. ...
... Given previous research (Molnar, 1991(Molnar, , 1998Carr, 1999;Rayfield, 2004Rayfield, , 2005aSnively et al., 2006;Molnar, 2008;Holliday, 2009;Bates and Falkingham, 2012;Gignac and Erickson, 2017), we know enough about Tyrannosaurus cranial anatomy to rigorously explore hypotheses of cranial behavior and function and examine the kinetic capacity of these forcefully biting ancient predators. The skulls of Tyrannosaurus and many other nonavian theropod dinosaurs maintain both upper and lower temporal bars, epipterygoids, dorsoventrally thin palatal elements, and robust scarf joints between elements of the dermatocranium and palate (Molnar, 1991(Molnar, , 1998Carr, 1999;Snively et al., 2006), all of which are features considered to limit cranial mobility (Holliday and Witmer, 2007). ...
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The extinct non‐avian dinosaur Tyrannosaurus rex, considered one of the hardest biting animals ever, is often hypothesized to have exhibited cranial kinesis, or, mobility of cranial joints relative to the braincase. Cranial kinesis in T. rex is a biomechanical paradox in that forcefully‐biting tetrapods usually possess rigid skulls instead of skulls with movable joints. We tested the biomechanical performance of a tyrannosaur skull using a series of static positions mimicking possible excursions of the palate to evaluate Postural Kinetic Competency in Tyrannosaurus. A functional extant phylogenetic bracket was employed using taxa which exhibit measurable palatal excursions: Psittacus erithacus (fore‐aft movement) and Gekko gecko (mediolateral movement). Static finite element models of Psittacus, Gekko, and Tyrannosaurus were constructed and tested with different palatal postures using anatomically‐informed material properties, loaded with muscle forces derived from dissection, phylogenetic bracketing, and a sensitivity analysis of muscle architecture and tested in orthal biting simulations using element strain as a proxy for model performance. Extant species models showed lower strains in naturally‐occurring postures compared to alternatives. We found that fore‐aft and neutral models of Tyrannosaurus experienced lower overall strains than mediolaterally‐shifted models. Protractor muscles dampened palatal strains, while occipital constraints increased strains about palatocranial joints compared to jaw‐joint constraints. These loading behaviors suggest that even small excursions can strain elements beyond structural failure. Thus, these postural tests of kinesis, along with the robusticity of other cranial features, suggest that the skull of Tyrannosaurus was functionally akinetic. This article is protected by copyright. All rights reserved.
... The Tyrannosauridae consist of several well-supported North American and Asian forms (Carpenter, 1990(Carpenter, , 1992Holtz, 1994;Carr, 1999;Carr and Williamson, 2000;Brochu, 2002;Currie, 2003a). This species was selected because it has an interesting dentition, is known from multiple individuals, and has a well-studied anatomy that would be complemented by an examination of the dental apparatus (see Osborn, 1905Osborn, , 1906Osborn, , 1912Osborn, , 1913Osborn, , 1917Carpenter, 1990Carpenter, , 1992Molnar, 1991Molnar, , 1998Carr, 1999;Carr andWilliamson, 2000, 2004;Brochu, 2002;Hurum and Sabath, 2003). As the functional aspects of T. rex teeth have been addressed elsewhere (Abler, 1992(Abler, , 1999(Abler, , 2001Erickson, 1996;Molnar, 1998), the emphasis here is placed on morphology. ...
... This species was selected because it has an interesting dentition, is known from multiple individuals, and has a well-studied anatomy that would be complemented by an examination of the dental apparatus (see Osborn, 1905Osborn, , 1906Osborn, , 1912Osborn, , 1913Osborn, , 1917Carpenter, 1990Carpenter, , 1992Molnar, 1991Molnar, , 1998Carr, 1999;Carr andWilliamson, 2000, 2004;Brochu, 2002;Hurum and Sabath, 2003). As the functional aspects of T. rex teeth have been addressed elsewhere (Abler, 1992(Abler, , 1999(Abler, , 2001Erickson, 1996;Molnar, 1998), the emphasis here is placed on morphology. ...
... The second and third maxillary teeth possess the 'classic' image FIGURE 5. Premaxillary tooth morphology in Tyrannosaurus rex. A, idealized skulls of T. rex and Dromaeosaurus in palatal view, showing variation in snout shape (after Molnar, 1998, andCurrie, 1995 of crowns of T. rex (e.g., FMNH PR2081). The mesial carinae, in mesial view, start at the middle of the apex and curve lingually such that at the base of the crown, they are completely on the lingual sides of the bases. ...
Article
Tyrannosaurus rex possesses a heterodont dentition composed of three classes (premaxillary, maxillary, and dentary) and several sets. The maxilla contains mesial and distal sets and the dentary contains first dentary tooth (d1), mesial, and distal sets. Teeth were described with four size and two shape variables and several variables describing crown curvature and denticle size. The premaxillary teeth are derived structures with labiolingually oriented long axes, moderate mesial curvature, and mesiolingually and distolingually placed carinae that extend down the lingual faces. The mesial maxillary crowns are large, basally rounded, and moderately curved with mesiodistally oriented long axes. The mesial carinae begin at the apices and curve lingually to about the midcrown point and the distal carinae begin at the apices and extend down the labial sides of the distal faces. The distal maxillary crowns are larger than the premaxillary and smaller than the mesial maxillary and all but the most distal dentary teeth. They have labiolingually oriented long axes and have narrower basal widths than lengths. The carinae roughly define the mesiodistal axes of the crowns. The first dentary tooth is similar to those of the premaxilla. The mesial dentary teeth are similar to the mesial maxillary teeth and the distal dentary teeth are similar to those in the distal maxilla. This examination revealed that several putative systematic characters related to size and shape can be discerned from T. rex teeth, suggesting that useful dental characters may be more common within the Theropoda than has generally been presumed.
... Although biomechanical models have been constructed for extant and extinct synapsids (e.g., Van Valkenburgh and Ruff 1987;Biknevicius and Ruff 1992a;Crompton 1995;Greaves 1995;Biknevicius and VanValkenburgh 1996; and references therein), crocodilians {e.g., Molnar 1969;Busbey 1989Busbey , 1995Drongelen and Dullemeijer 1982;Sinclair and Alexander 1987;Therrien and Ruff, in prep.), some ornithischian dinosaurs (Ostrom 1961(Ostrom , 1964Weishampel 1983Weishampel , 1984Norman 1984), and the gigantic bird Diatryma (Witmer and Rose 1991 ), only recently have theropod jaw biomechanics been investigated in detail (e.g., Mazzetta et al. 1998;Molnar 1998;Rayfield et al. 2001). We expand upon this work, taking a biomechanical approach to analyze feeding behavior in different groups of non-avian theropods. ...
... The third assumption has its origin in the methods used. By using external measurements to model a mandible as a solid elliptical beam, we ignore both the variation in the internal structure of the mandible (i.e., thickness of cortical bone, hollow mandible in the postdentary region versus solid mandible in the dentary region; see Molnar 1998;Brochu and Ketcham 2002) and its deviation from a perfect elliptical shape. Fortunately, comparison of results obtained from computed tomography (CT) scans and external dimensions in Alligator mississippiensis (Therrien and Ruff, in prep.) has revealed that a simplified beam model based on external measurements can be used to study accurately the relative biomechanical changes along the mandible, although the model somewhat overestimates their absolute values when the mandible is not truly solid (also see Biknevicius and Ruff 1992b). ...
... However, since the main interest here lies in making interspecific comparisons of changes in dorsoventral, labiolingual, and relative mandibular force along the mandible rather than providing bite force estimates in absolute values (in Newtons), the assumption of a solid mandible will not invalidate the beam models presented here. Furthermore, because the mandibles of theropods can presumably be considered to be truly solid (Molnar 1998;Van Valkenburgh and Molnar 2002), the cross-sectional properties determined from the simplified beam models should be dose to the real values. More-accurate biomechanical properties could be determined by conducting CT scans of mandibles, but, especially in the case of large or mounted specimens, specimens filled with matrix, or specimens located at institutions without CT facilities, this approach is problematic, time consuming, and costly. ...
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A biomechanical approach is used to study feeding behavior in non-avian theropods. Mandibles can be modeled as beams undergoing bending loads during food ingestion. The bite force applied at any given point along the mandible should be proportional to the external dimensions of the mandibular ramus at that location. Thus, patterns of variation in these dimensions reflect the adaptation of the jaw to specific loads, which are related to the method of killing prey. These beam models were compared to those of the extant varanids Varanus komodoensis (Komodo dragon, an ambush predator with a slashing bite) and Varanus niloticus (Nile monitor, molluscivorous) to gain insight into the feeding behavior of theropods. On the basis of our results, we identified five distinct theropod feeding categories: (1) the allosauroid "Antrodemus valens" and the abelisaurids Majungatholus atopus and Carnotaurus sastrei share the mandibular properties of the Komodo dragon, and these shared properties, combined with the similarity between the craniodental morphology of "Antrodemus" and Majungatholus and that of the varanid, suggest that they were probably large-prey hunters delivering slashing bites; (2) dromaeosaurids have mandibular properties reminiscent of those of V. komodoensis for slashing bites, but differences can be identified between Dromaeosaurus and velociraptorines, the former having a stronger bite than the latter, suggesting that it possibly relied more on its jaws to capture and kill prey; (3) Suchomimus tenerensis and Dilophosaurus wetherilli exhibit mandibular adaptations related to the capture of prey smaller than themselves, the former probably practicing a bite-and-hold strategy and the latter finishing its prey with slashing bites; (4) Ceratosaurus nasicornis, Allosaurus fragilis, Acrocanthosaurus atokensis, and Giganotosaurus carolinii demonstrate adaptations of the anterior extremity of the mandible for capturing prey and delivering powerful bites to bring down prey or deliver the final blow; and (5) tyrannosaurids, unlike other theropods, exhibit mandibular adaptations to resist high torsional stresses at the anterior of the mandible induced during prey capture, bone crushing, or both. The mandibular models were also used to infer relative bite force in theropods. Velociraptorines appear to have had a maximum bite force similar to that of V. komodoensis, whereas that of Dromaeosaurus was three times as great. Suchomimus, Allosaurus, "Antrodemus," and Ceratosaurus were capable of exerting maximum bite forces as great as A. mississippiensis, and those of abelisaurids and Albertosaurus were twice as powerful. Among the largest theropods, Acrocanthosaurus and Giganotosaurus were surpassed by Daspletosaurus and Tyrannosaurus. The high estimates obtained for tyrannosaurids are consistent with previously published values that suggest bone-cracking abilities. Growth series for Allosaurus fragilis, Albertosaurus sarcophagus, Gorgosaurus libratus, and Tyrannosaurus rex were also studied in order to determine whether mandibular properties changed during ontogeny. Significant changes were observed in Allosaurus, especially in bending rigidity, indicating that juveniles did not feed the same way as adults; juveniles probably delivered simple slashing bites. Unfortunately, the question of parental care in Allosaurus cannot be resolved in light of our results. The mandibular properties of tyrannosaurids were not found to vary significantly during ontogeny, other than in terms of bite force. This finding strongly suggests that juveniles were apt predators, capable of subduing their own prey rather than relying on carrion or parental care to survive.
... The Tyrannosauridae consist of several well-supported North American and Asian forms (Carpenter, 1990(Carpenter, , 1992Holtz, 1994;Carr, 1999;Carr and Williamson, 2000;Brochu, 2002;Currie, 2003a). This species was selected because it has an interesting dentition, is known from multiple individuals, and has a well-studied anatomy that would be complemented by an examination of the dental apparatus (see Osborn, 1905Osborn, , 1906Osborn, , 1912Osborn, , 1913Osborn, , 1917Carpenter, 1990Carpenter, , 1992Molnar, 1991Molnar, , 1998Carr, 1999;Carr andWilliamson, 2000, 2004;Brochu, 2002;Hurum and Sabath, 2003). As the functional aspects of T. rex teeth have been addressed elsewhere (Abler, 1992(Abler, , 1999(Abler, , 2001Erickson, 1996;Molnar, 1998), the emphasis here is placed on morphology. ...
... This species was selected because it has an interesting dentition, is known from multiple individuals, and has a well-studied anatomy that would be complemented by an examination of the dental apparatus (see Osborn, 1905Osborn, , 1906Osborn, , 1912Osborn, , 1913Osborn, , 1917Carpenter, 1990Carpenter, , 1992Molnar, 1991Molnar, , 1998Carr, 1999;Carr andWilliamson, 2000, 2004;Brochu, 2002;Hurum and Sabath, 2003). As the functional aspects of T. rex teeth have been addressed elsewhere (Abler, 1992(Abler, , 1999(Abler, , 2001Erickson, 1996;Molnar, 1998), the emphasis here is placed on morphology. ...
... The second and third maxillary teeth possess the 'classic' image FIGURE 5. Premaxillary tooth morphology in Tyrannosaurus rex. A, idealized skulls of T. rex and Dromaeosaurus in palatal view, showing variation in snout shape (after Molnar, 1998, andCurrie, 1995 of crowns of T. rex (e.g., FMNH PR2081). The mesial carinae, in mesial view, start at the middle of the apex and curve lingually such that at the base of the crown, they are completely on the lingual sides of the bases. ...
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Tyrannosaurus rex possesses a heterodont dentition composed of three classes (premaxillary, maxillary, and dentary) and several sets. The maxilla contains mesial and distal sets and the dentary contains first dentary tooth (d1), mesial, and distal sets. Teeth were described with four size and two shape variables and several variables describing crown curvature and denticle size. The premaxillary teeth are derived structures with labiolingually oriented long axes, moderate mesial curvature, and mesiolingually and distolingually placed carinae that extend down the lingual faces. The mesial maxillary crowns are large, basally rounded, and moderately curved with mesiodistally oriented long axes. The mesial carinae begin at the apices and curve lingually to about the midcrown point and the distal carinae begin at the apices and extend down the labial sides of the distal faces. The distal maxillary crowns are larger than the premaxillary and smaller than the mesial maxillary and all but the most distal dentary teeth. They have labiolingually oriented long axes and have narrower basal widths than lengths. The carinae roughly define the mesiodistal axes of the crowns. The first dentary tooth is similar to those of the premaxilla. The mesial dentary teeth are similar to the mesial maxillary teeth and the distal dentary teeth are similar to those in the distal maxilla. This examination revealed that several putative systematic characters related to size and shape can be discerned from T. rex teeth, suggesting that useful dental characters may be more common within the Theropoda than has generally been presumed.
... Meaning ''sword tooth,'' it is characterized by labio-lingually compressed, distally curved, serrated crowns. The serrated carinae have a true series of individualized denticles (Langston 1975;Prasad and Lapparent de Broin 2002;Molnar 2004). These attributes occur in varying degrees among these different taxa (Farlow et al. 1991;Smith et al. 2005). ...
... It occurs only in certain members of the squamate family Varanidae (Auffenberg 1981). These crowns are morphologically very similar to their extinct counterparts, and excavators have confused isolated crowns of ziphodont crocodilians for large varanid teeth (Molnar 2004). The crowns of modern crocodilians and the canines of mammalian carnivores are robust and conical, and lack true denticles (Prasad and Lapparent de Broin 2002). ...
... Farlow et al. (1991) speculated on the function of denticulated crowns by applying serrated cutting mechanics as outlined by Frazzetta (1988). These exceptions aside, morphometric studies of ziphodonts tend to focus solely on the taxonomic identification of isolated teeth (Chandler 1990;Currie et al. 1990;Molnar 1998;Sankey et al. 2002;Sweetman 2004;Smith 2005Smith , 2007Smith et al. 2005). In one of the few experiments on denticulated crown performance, Abler (1992) examined the forces involved in cutting and puncturing various substrates in tyrannosaurids. ...
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Most functional interpretations of ziphodont dentition are based on limited morphometric, behavioral, and taphonomic studies, but few are based on controlled observations of a modern ziphodont consumer. The purpose of this study is to determine through controlled feeding observations if the behaviors indicative of a ziphodont consumer are reflected by tooth marks left on bone surfaces by Varanus komodoensis, the Komodo monitor. We document feeding behavior, expand upon dental function, and correlate these aspects with tooth mark production. We also discuss the significance and limits of applying these data to fossil assemblages. Goat carcasses were fed to 11 captive individuals. V. komodoensis modifies bone surfaces extensively. Individuals exhibit a “medial-caudal arc'7 when defleshing, followed by inertial swallowing. Bone crushing was not observed. The vast majority of tooth marks are scores, with pits being significantly less common. Tooth furrows and punctures are rare. “Edge marks” are produced on flat elements. Marks are elongate and narrow, with variable lengths and curvature. Over one-third of the marks occur within parallel clusters. Striations are evident on 5% of all marks. Both feeding behavior and tooth marks indicate that ziphodont crowns are ideal for defleshing by being drawn distally through a carcass. Crowns are poorly built for crushing, and within-bone nutrients are acquired through swallowing. Mark production is a by-product of the distal crown movement during the flesh removal process. Scores are the consequence of apical dragging. Edge marks and striated scores result respectively from distal and mesial carinae contact. Mark curvature is the consequence of arcing motions. Parallel clusters may result from repetitive defleshing strokes and/or from multiple crown contacts during a stroke. These observations can be used to draw functional, behavioral, and taphonomic interpretations from fossil assemblages. When they are provisionally applied to theropod tooth marks, similar crown function and defleshing behavior with little bone crushing is apparent. Differences occur concerning mark frequency and curvature, relating potentially to taphonomic biases and rostral motion, respectively.
... 18): " as the upper teeth closed outside those of the mandible any wear, not on the point, would result from the contact of the inner surface of the upper teeth with the outer surface of the lower ones. " Recent workers, have, however, challenged this assertion, suggesting that the shapes, locations, and incidences of tyrannosaurid wear surfaces are not indicative of tooth−tooth contact (Farlow and Brinkman 1994; Molnar 1998; Jacobsen 1996 Jacobsen , 2003). Here we reevaluate this evidence by examining wear striations in tyrannosaurid lateral teeth in addition to the shapes and locations of their wear surfaces. ...
... Discussion Lambe (1917) suggested that wear surfaces found on the sides of lateral teeth of tyrannosaurids resulted from tooth−tooth contact during feeding. More recent works have suggested that these surfaces must have a different etiology (Farlow and Brinkman 1994; Molnar 1998; Jacobsen 2003). For example, Farlow and Brinkman (1994) note the presence of wear on the inner sides of tyrannosaurid and Komodo dragon dentary teeth. ...
... Differ− ences between the pattern on wear surfaces and adjacent enamel indicate that facet wear is antemortem and not the re− sult of taphonomic damage. While it has been suggested that these wear facets may be related to tooth−food contact (e.g., Molnar 1998), the consistency in orientation (approximately 15 degrees from the long axis of the facet) of the relatively large parallel striations, and the fact that these striations match the expected direction of a vertically−oriented bite (see Molnar 1988:fig. 15) and tooth−tooth contact makes an attrition explanation more likely. ...
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2005. Wear facets and enamel spalling in tyrannosaurid dinosaurs. Acta Palaeontologica Polonica 50 (1): 93–99. Numerous paleontologists have noted wear facets on tyrannosaurid lateral teeth over the past century. While several workers have proposed explanations for these features, there remains to this day no consensus concerning their etiology. Here we report on an examination of wear surfaces on these teeth from the Upper Cretaceous (mid−Campanian) Judith River Group of southern Alberta, Canada. This study reveals two distinct types of wear features on the labial and lingual sides of tyrannosaurid lateral teeth: irregular "spalled" surfaces and wear facets. The irregular spalled surfaces typically extend to the apex of the tooth, which evidently reflects flaking of enamel resulting from forces produced during contact between tooth and food. These surfaces are often rounded, presumably from antemortem wear following spalling. Wear striations on these surfaces are oriented heterogeneously. The wear facets, in contrast, occur on only one side of the tooth and are typically elliptical in outline and evince parallel wear striations. Similar patterns of parallel wear striations in ex− tant mammals reflect tooth−tooth contact. We therefore propose that wear facets in tyrannosaurids were formed by re− peated tooth−tooth contact between the lingual side of maxillary teeth and labial side of dentary teeth. It remains unclear whether this contact was serendipitous or adaptive, though it appears to be unusual for reptiles, as we have found no evidence for wear facets in extant varanids and crocodilians.
... The Ty− rannosauridae were giant coelurosaurian theropods from the Cretaceous of Asia and North America (Holtz 1994Holtz , 2004). Tyrannosaurids differ from both smaller coelurosaurs and other large theropods including carnosaurs (Fig. 1; Hutchin− son and Padian 1997) in the greater robustness of their teeth (Farlow et al. 1991) and skulls (Henderson 2002; Therrien et al. 2005), enlarged areas for attachment and expansion of jaw muscles (Molnar 1973Molnar , 2000), and the consequent ability to bite deeply into bone (Abler 1992; Carpenter 2000; Chin 1998; Meers 2003). Among other spe− cific adaptations suggested for this activity, adult tyranno− saurid mandibles were stronger than those of other large theropods (Fig. 2). ...
... The teeth were the el− ements that would first encounter resistance of prey tissues and would transmit food reaction forces to the cranium. Tyrannosaurid nasals were potentially adapted to resisting those forces, as dorsally positioned compressive members of the truss−like cranium (Molnar 2000; Rayfield 2004). We chose this order of investigation because each inductive stage can potentially falsify our overall hypothesis of corre− lated progression, and will build up to an integrated picture of the strengths of theropod feeding apparatus. ...
... To compare these strengths, we used simple engineering principles and calculations. Simplified models of biological structures have a rich history in the palaeontological and neontological literature (Alexander 1985; Farlow et al. 1995; Greaves 1978 Greaves , 1991 Henderson 2002; Holtz 1995; Molnar 2000; Slijper 1946; Thomason and Russell 1986; Thompson 1917). Simple approximations are valuable for numerous reasons, especially in palaeontology. ...
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2006. Fused and vaulted nasals of tyrannosaurid dinosaurs: Implications for cranial strength and feeding mechanics. Acta Palaeontologica Polonica 51 (3): 435–454. Tyrannosaurid theropods display several unusual adaptations of the skulls and teeth. Their nasals are fused and vaulted, suggesting that these elements braced the cranium against high feeding forces. Exceptionally high strengths of maxillary teeth in Tyrannosaurus rex indicate that it could exert relatively greater feeding forces than other tyrannosaurids. Areas and second moments of area of the nasals, calculated from CT cross−sections, show higher nasal strengths for large tyrannosaurids than for Allosaurus fragilis. Cross−sectional geometry of theropod crania reveals high second moments of area in tyrannosaurids, with resulting high strengths in bending and torsion, when compared with the crania of similarly sized theropods. In tyrannosaurids trends of strength increase are positively allomeric and have similar allometric expo− nents, indicating correlated progression towards unusually high strengths of the feeding apparatus. Fused, arched nasals and broad crania of tyrannosaurids are consistent with deep bites that impacted bone and powerful lateral movements of the head for dismembering prey.
... Jaw muscles are, by far, the most-studied muscular system of the dinosaur head and, along with tooth morphology (e.g., Van Heerden, 1997) and skull mechanical analysis (e.g., Molnar, 1998;Rayfield et al., 2001Rayfield et al., , 2004Rayfield et al., , 2005Henderson, 2003), are the most commonly used predictors of feeding biology and jaw function (Table 1.1). ...
... Jaw muscles have been reconstructed in numerous fossil archosaurs including basal archosaurs (Anderson, 1936;Crompton and Attridge, 1986;Walker, 1990), basal dinosaurs (Romer, 1966;Attridge, 1986, Galton, 1986), ankylosaurs (Haas, 1969), ceratopsians (Lull, 1908;Russell, 1935;Haas, 1955;Ostrom, 1964Ostrom, , 1966Dodson, 1996), ornithopods (Ostrom, 1961;Galton, 1974;Weishampel, 1984;Crompton and Attridge, 1986), sauropods (Janensch 1936;Haas, 1963;Zhang 1988), non-avian theropods (Adams 1919;Molnar 1973Molnar , 1998Raath 1977;Horner and Lessem, 1993;Witmer, 1997;Bakker, 1998;Rayfield et al., 2001;Bimber et al., 2002), and birds (Bühler et al., 1988;Witmer and Rose, 1991). ...
... Moreover, such reconstructions of muscles, or other soft tissues for that matter, can significantly affect functional hypotheses of not only the muscles but also other neighboring systems, such as pneumatic or sensory structures. For instance, the role of the antorbital cavity has been postulated to be the attachment site of the dorsal pterygoideus muscle (Adams, 1919;Molnar, 1973Molnar, , 1998Bakker, 1986;Horner and Lessem, 1993). The muscle was hypothesized to attach on the lateral margin of the antorbital cavity, then course medially into the antorbital fossa, over the dorsal surface of the palate, and then attach to the medial surface of the mandible ( Fig.1.2A). ...
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Crocodilians, dinosaurs, and birds are part of successful group of reptiles known as archosaurs, little is known about the evolution of the adductor chamber, which includes the jaw musculature, trigeminal nerves, and particular blood vessels, hindering hypotheses of homology and feeding function in fossil taxa such as crocodyliforms and non-avian dinosaurs. First, I review the cephalic musculature of dinosaurs and identify problems and prospects involved in inferring feeding form and function in the clade. Second, using a flamingo as a case study, I introduce a new CT imaging/dissection methodology that enables 3D visualization of cephalic vasculature and differentiation of adductor chamber contents. Third, I develop a robust hypothesis of jaw muscle homology by analyzing the topological patterns of soft tissues in the adductor chambers of extant reptiles. Fourth, I identify major evolutionary changes in the orbitotemporal region (e.g., trigeminal nerve, braincase, palate) during the evolution of crocodilians. Fifth, I identify major evolutionary changes in the orbitotemporal region of dinosaurs with respect to the evolution of birds. Sixth, I discuss the evolution of cranial kinesis and its functional significance in dinosaurs and other reptiles. The general results were: 1) Flamingos have a novel vascular device associated with the hyolingual system. 2) Crocodylians have a novel soft-tissue topological pattern that violates the trigeminal topological paradigm. 3) Sensory branches of the trigeminal nerves are topologically conservative and represent evolutionarily stable dermatomes. 4) Despite the suturing of the palate to the braincase early in their evolution, the epipterygoid was a persistent structure in the skull of crocodyliforms, evolved several different morphotypes, and was not eliminated until recently along the lines to modern crocodylians. 5) The trigeminal nerve, protractor muscles, and epipterygoid exhibit mosaic evolution among dinosaurs and prove to be phylogenetically and functionally informative structures. 6) Dinosaurs do not exhibit the suite of morphological characters indicative of cranial kinesis which suggests that intracranial synovial joints may more likely be related to growth rather than feeding function. Hence, jaw musculature and its neighboring tissues in the adductor chamber are key cephalic structures that exhibit characteristic morphological, functional, and phylogenetic patterns among extant and fossil archosaurs. System requirements: Adobe Acrobat reader. Mode of access: World Wide Web via OhioLINK's ETD Center. Title from PDF title page (viewed on Jan. 27, 2007). Thesis (Ph. D.)--Ohio University, 2006. Includes bibliographical references (p. 209-236).
... Therefore, theropod functional morphology in the context of feeding behavior has been investigated from many perspectives. Modeling cranial structuring, musculature, and kinesis has given insight into the skull's resistance to stress, potential bite force, and niche partitioning among species (Busbey, 1995;Henderson, 1998Henderson, , 2002Mazzetta et al., 1998;Molnar, 1998;Rayfield et al, 2001Rayfield et al, , 2007Rayfield, 2004). Forelimb structure indicates a range of ability for securing prey with the manus (Holtz, 2002;Ostrom, 1969;Sereno, 1993;Tykoski and Rowe, 2004). ...
... Several comparative morphometric studies have been conducted on the diversity of theropod teeth, but most of these have focused primarily on the description and/or taxonomic identification of isolated teeth (Carr and Williamson, 2004;Currie et al., 1990;Molnar, 1998;Sadlier and Chapman, 1999;Sankey et al., 2002;Smith 2005Smith , 2007Smith et al., 2005;Samman et al., 2005). Consequently, there has been little analysis of dental function. ...
... Finding a repeatable method for identifying the apex has proven difficult in the past, because the apex is often rounded and may occupy a large area . Many studies do not detail how the apex is identified (Henderson, 2002;Molnar, 1998;Rieppel, 1979;Sankey et al., 2002) and others derive tooth heights instead of apex positions (Farlow et al., 1991;Smith et al., 2005;Smith, 2005Smith, , 2007. I defined the apex as the point along the tooth where the most acute angle is formed and the two carinae meet. ...
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The serrated, or denticulated, ziphodont teeth of theropod dinosaurs display variability in their extent of denticulation. The functional model proposed here tests the hypothesis that denticles will not exist in areas that do not frequently contact the substrate. This area, defined as the "dead-space," is determined by the direction the tooth moves through the fleshy substrate. The extent of denticulation, as well as the dead-space dimensions, is measured from photographs of 235 isolated and in situ theropod teeth, to determine a meaningful relationship between the two variables. Both Euclidean and geometric morphometric methods are employed, and the data are expressed in bivariate and ordination plots. The model predicts the direction of tooth movement through the curvature of the tip/apex. Tooth position and taxon are considered. The results show that the mesial margin is usually partially denticulated, while the distal margin is usually totally denticulated. Curved teeth have large dead-spaces, and tend to be less denticulated mesially. Straighter teeth are more extensively denticulated, to the point where they became symmetrical. The mesial denticulation is determined by the dead-space, and dictated by the substrate contact. The dead-space almost always predicted less extensive denticulation; a consequence of the model's limitations. Tooth curvature increases with a more distal position, due to rotation based on the proximity to the hinge. Denticulation indicates that theropods used a distally oriented puncture to modify the substrate, similar to modern analogues. Although there is little taxonomic variation, Troodontidae show unique and extreme degrees of mesial denticulation.
... Demonstration of a relationship between bite force and body size in extant taxa led to the prediction that T. rex could generate a bite force of between 183000 and 235000 Newtons [24], although this range is substantially higher than empirically derived estimates [16]. Further inferences of skull strength have been provided by space-frame analysis [25], which has suggested that the skull of T. rex was constructed primarily to resist strong, vertically directed bite forces during biting: this result has been used to argue for carcass dismemberment through repeated biting rather than extensive lateral shaking of prey, which, by contrast, would have resulted in the application of large, laterally directed loads to the teeth [25]. ...
... Demonstration of a relationship between bite force and body size in extant taxa led to the prediction that T. rex could generate a bite force of between 183000 and 235000 Newtons [24], although this range is substantially higher than empirically derived estimates [16]. Further inferences of skull strength have been provided by space-frame analysis [25], which has suggested that the skull of T. rex was constructed primarily to resist strong, vertically directed bite forces during biting: this result has been used to argue for carcass dismemberment through repeated biting rather than extensive lateral shaking of prey, which, by contrast, would have resulted in the application of large, laterally directed loads to the teeth [25]. ...
... Instead, the teeth were used to 'grip-and-rip' prey -the 'puncture-pull' feeding hypothesis [17,18]. Spaceframe analysis suggests that the T. rex skull was constructed to resist strong, vertically directed bite forces [25]. FEA provides information on stress-strain patterns within the skull, and confirms that the T. rex cranium could withstanding large feeding-induced puncture-pull loads [34] (Figure Ie). ...
Article
Dinosaurs had a wide variety of feeding mechanisms that strongly impacted on their ecology and evolution. Here, we show how novel application of technologies borrowed from medicine and engineering, such as CT scanning and Finite Element Analysis, have recently been combined with traditional approaches to result in significant advances in our understanding of dinosaur palaeobiology. Taxon-specific studies are providing quantitative data that can be used to generate and test functional hypotheses relating to jaw mechanics and feeding behaviour. In turn, these data form a basis for investigating larger scale patterns of ecological and macroevolutionary change, such as possible coevolutionary interactions and the influence of feeding adaptations on species richness, which are of more general interest to ecologists and evolutionary biologists.
... The scavenger argument has been met with skepticism by other workers (e.g., Holtz, 2008;Krauss and Robinson, 2013;Nesteruk, 2019). It has been demonstrated that the jaws of tyrannosaurids and, in particular, T. rex are reinforced vertically, which helped to create exceptional biting power (e.g., Thomson, 1966;Molnar and Farlow, 1990;Molnar, 1998;Kemp, 1999;Hurum and Currie, 2000;Hurum and Sabath, 2003;Rayfield, 2004;Therrien et al., 2005;Snively et al., 2006). Tyrannosaurid teeth and the skull, particularly of Tyrannosaurus rex are more robust than that of other large theropods (Farlow et al., 1991;Abler, 1992;Brochu, 2003;Hutchinson and Padian, 1997;Henderson, 2002;Therrien et al., 2005;Reichel, 2010). ...
... Tyrannosaurid teeth and the skull, particularly of Tyrannosaurus rex are more robust than that of other large theropods (Farlow et al., 1991;Abler, 1992;Brochu, 2003;Hutchinson and Padian, 1997;Henderson, 2002;Therrien et al., 2005;Reichel, 2010). The skulls have large areas 40 for attachment and expansion of upper and lower jaw muscles that allowed for a powerful bite deep into bone (Carpenter, 1998;Molnar, 1998;Meers, 2002). The dentaries of large tyrannosaurids have high section moduli that could withstand high force during feeding than in equivalently sized non-avian theropods (e.g., Therrien et al., 2005), and also have anterodorsally inclined intermandibular symphysis, which are enhanced dorsally by the anterior step of the dorsal lingual lamina (=anterior step of the lingual bar of Dalman andLucas, 2015, 2017a). ...
Chapter
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An isolated anterior left dentary, proximal caudal centrum and an isolated right femur pertaining to adult, subadult and juvenile tyrannosaurid dinosaurs from the Upper Cretaceous deposits of the San Juan Basin in New Mexico preserve several bite marks and other feeding traces made by another tyrannosaurid. The dentary was recovered from the Ne-nah-ne-zad Member of the Fruitland Formation (Campanian); whereas, the femur was recovered from De-na-zin Member of the Kirtland Formation (Campanian), and the isolated caudal centrum was recovered from the Naashoibito Member of the Ojo Alamo Formation (Maastrichtian). The presence of bone surface healing around the bite marks in the dentary indicate that the biting occurred pre-mortem; whereas, the absence of bone surface healing around the bite marks in the caudal centrum and the right femur indicates the biting most likely took place post-mortem. Intensely tooth-marked bones clearly show that the San Juan Basin tyrannosaurids attacked and fed upon the remains of not only their most common prey such as ceratopsians, hadrosaurs, and sauropods, but also conspecifics. The bite marks described here represent four categories: bite-and-drag, drag-and-scrape, puncture, and puncture-and-collapse. The specimens provide new evidence for cannibalism among tyrannosaurids. Although extensively tooth marked, these bones do not support the previous assumptions of selective feeding behavior of these iconic predators based on inferred bite marks.
... Because of its large body size, there is immense interest in the feeding process of Tyrannosaurus. There has been modelling of cranial structuring, musculature, and kinesis of the skull of T. rex that has offered an understanding of the skull's resistance to stress and probable bite force (Molnar 1991(Molnar , 1998Rayfield et al. 2001;Meers 2002;Henderson 2003;Rayfield 2004;Reichel 2010). Osborns (1912) study is still one of the best prior treatments of Tyrannosaurus dentition, but other works have also discussed the teeth with regard to their heterodont morphology and taxonomic value (e.g. ...
... The premaxillary teeth are laterally compressed. The roughly incisiform and spatulate teeth are typically D-shaped in cross-section (Osborn 1912;Molnar 1991Molnar , 1998Brochu 2003), with a nearly flattened lingual (internal) surface and a broadened and convex labial (external) surface. The orientation of the long-axis is obliquely mesiodistally directed. ...
Article
A well-preserved skull of Tyrannosaurus rex from the Late Cretaceous (Maastrichtian) Hell Creek Formation of Montana is used to document its tooth replacement with the help of high-resolution medical CT scanning. A pattern of retaining only one single replacement tooth before replacing the functional tooth is reconstructed for most alveoli of the jaws, with exception of the second alveolus of the left maxilla, and the fourth alveolus of the right dentary, where another, second replacement tooth can be seen. The youngest replacement teeth have only a thin layer of enamel around the tooth crown, the larger replacement teeth have thicker enamel, fortified at the apex as in the functional teeth. The Zahnreihen approach allows to reconstruct a z-spacing of 2 in the upper jaws, whereas the right dentary displays a z-spacing of 1 in the rostral and distal third of the tooth row and a z-spacing of 2 in its medial part. In MB.R.91216, teeth of the upper jaws and the medial part of the dentary were probably replaced in a regular alternating pattern between odd and even teeth, whereas the mesial and distal teeth of the dentary were replaced simultaneously.
... The taxonomic classification of the analysed fossil assemblage follows the identifications proposed by Candeiro et al. (2012). The classification of the pattern of tooth wear follows the proposals of Molnar (1998), Schubert & Ungar (2005) and Hendrickx et al. (2015). ...
... The patterns of wear surfaces, such as their attritional striations and oval shapes, were probably formed by their effective cutting teeth (like a scissor with serrated blades), which was similarly observed by Schubert & Ungar (2005) on tyrannosaurid teeth. This type of occlusion is probably related to higher bite forces that produce striations on the lingual and labial surfaces, extending to the crown surfaces of the teeth -a feature similar to those observed by Molnar (1998). The seemingly powerful bite force of these theropods could have produced the abrupt fractures present on the specimens described here. ...
Article
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Little is known about the tooth wear of South American theropod dinosaurs. This paper describes wear facets in Abelisauridae, Carcharodontosauridae and some indeterminate theropods teeth, from the Marília Formation. Four types of wear facets are proposed: vertically-oriented attritional striations; perpendicular attritional surfaces; oval wear facets; and apical grooves. All these worn surfaces were produced by dental occlusion, except the apical grooves, which are produced by the contact between predator teeth and the prey bone during predator–prey interaction. More detailed biomechanical and hardness testing of teeth and bone may further elucidate the pattern of tooth wear in theropods.
... obs.; Appendix, Fig. A4F). Tyrannosaurid teeth also display similar crown ornamentations, but their lateral teeth are much stouter and the mesialmost teeth have a mesial carina displaced lingually, rather than mesially or labially (e.g., Molnar 1998;Smith 2005;Samman et al. 2005;Holtz 2003Holtz , 2004Holtz , 2008. ...
... Tyrannosauroids can be differentiated from other theropods based mostly on the morphology of their mesialmost teeth. Indeed, the basal cross-section of the mesialmost crown is usually U-shaped (i.e., the mesial and distal carina are strongly displaced and face lingually or linguodistally; Appendix, Fig. A1I-J), the third and fourth premaxillary teeth are distinctively overlapping, and the posterior premaxillary teeth are significantly smaller than the anterior maxillary teeth (e.g., Paul 1988;Molnar 1998;Holtz 2004;Samman et al. 2005;Smith 2005). The mesialmost maxillary and dentary teeth of tyrannosauroids are also significantly smaller than the mid-maxillary and dentary teeth, respectively, and the crowns display an oriented enamel texture (although not present in some tyrannosaurids), contrary to most other coelurosaurs. ...
Article
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Theropod dinosaurs form a highly diversified clade, and their teeth are some of the most common components of the Mesozoic dinosaur fossil record. This is the case in the Lourinhã Formation (Late Jurassic, Kimmeridgian-Tithonian) of Portugal, where theropod teeth are particularly abundant and diverse. Four isolated theropod teeth are here described and identified based on morphometric and anatomical data. They are included in a cladistic analysis performed on a data matrix of 141 dentition-based characters coded in 60 taxa, as well as a supermatrix combining our dataset with six recent datamatrices based on the whole theropod skeleton. The consensus tree resulting from the dentition-based data matrix reveals that theropod teeth provide reliable data for identification at approximately family level. Therefore, phylogenetic methods will help identifying theropod teeth with more confidence in the future. Although dental characters do not reliably indicate relationships among higher clades of theropods, they demonstrate interesting patterns of homoplasy suggesting dietary convergence in (1) alvarezsauroids, therizinosaurs and troodontids; (2) coelophysoids and spinosaurids; (3) compsognathids and dromaeosaurids; and (4) ceratosaurids, allosauroids and megalosaurids. Based on morphometric and cladistic analyses, the biggest tooth from Lourinhã is referred to a mesial crown of the megalosaurid Torvosaurus tanneri, due to the elliptical cross section of the crown base, the large size and elongation of the crown, medially positioned mesial and distal carinae, and the coarse denticles. The smallest tooth is identified as Richardoestesia, and as a close relative of R. gilmorei based on the weak constriction between crown and root, the "eight-shaped" outline of the base crown and, on the distal carina, the average of ten symmetrically rounded denticles per mm, as well as a subequal number of denticles basally and at mid-crown. Finally, the two medium-sized teeth belong to the same taxon and exhibit pronounced interdenticular sulci between distal denticles, hooked distal denticles for one of them, an irregular enamel texture, and a straight distal margin, a combination of features only observed in abelisaurids. They provide the first record of Abelisauridae in the Jurassic of Laurasia and one of the oldest records of this clade in the world, suggesting a possible radiation of Abelisauridae in Europe well before the Upper Cretaceous.
... Tyrannosaurus possesses extremely robust, transversely expanded crania with stout interfenestral bars that encroach into the orbit and lower temporal fenestrae. Positional variability in tooth form is observed, with U-shaped premaxillary teeth and maxillary teeth becoming stout, almost conical in morphology (Farlow et al ., 1991; Molnar, 1998; Hurum & Sabath, 2003). The aim of this analysis was to compare the mechanical performance of crania during biting, and identify similarities and differences in stress and strain distribution and orientation between taxa. ...
... Alternatively, stress/strain patterns may conform in all three models, reflecting similar mechanical parameters (that may be phylogenetically or otherwise constrained ) or the fact that stress flows within the cranium are opportunistic ( sensu Preuschoft & Witzel, 2002 ), with stress disseminating throughout all available bony tissue. Furthermore, if the skull behaves as a beam during biting (Molnar, 1998), the dorsal skull will be compressed as the ventral skull is tensed and the interfenestral bars that lie about the neutral axis of bending should experience little or no stress. ...
Article
The engineering analysis technique finite element analysis (FEA) is used here to investigate cranial stress and strain during biting and feeding in three phylogenetically disparate theropod taxa: Coelophysis bauri, Allosaurus fragilis and Tyrannosaurus rex. Stress patterns are generally similar in all taxa with the ventral region of the skull tensed whilst the dorsal aspect is compressed, although the skull is not purely behaving as a cantilever beam as there is no discernible neutral region of bending. Despite similarities, stress patterns are not wholly comparable: there are key differences in how certain regions of the skull contain stress, and it is possible to link such differences to cranial morphology. In particular, nasal morphology can be explained by the stress patterns revealed here. Tyrannosaurus models shear and compress mainly in the nasal region, in keeping with the indistinguishably fused and expanded morphology of the nasal bones. Conversely Allosaurus and Coelophysis models experience peak shear and compression in the fronto-parietal region (which is tightly interdigitated and thickened in the case of Allosaurus) yet in contrast the nasal region is lightly stressed, corresponding to relatively gracile nasals and a frequently patent internasal suture evident in Allosaurus. Such differences represent alternate mechanical specializations between taxa that may be controlled by functional, phylogenetic or mechanical constraints. Creation of finite element models placed in a phylogenetic context permits the investigation of the role of such mechanical character complexes in the cranium of nonavian theropods and the lineage leading towards modern birds. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 144, 309–316.
... As demonstrated for the hypothetical skull models (Figs. 7, 8) circular orbits would increase stresses (in particular tensile stress) in the lacrimal and postorbital bones. The same regions are reinforced in carnivorous theropods 24,30 suggesting that these skeletal elements and their morphological arrangement play a key role in distributing feeding-induced stresses. The presence of (patent) sutures around the orbital bones (i.e. ...
Article
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The orbit is one of several skull openings in the archosauromorph skull. Intuitively, it could be assumed that orbit shape would closely approximate the shape and size of the eyeball resulting in a predominantly circular morphology. However, a quantification of orbit shape across Archosauromorpha using a geometric morphometric approach demonstrates a large morphological diversity despite the fact that the majority of species retained a circular orbit. This morphological diversity is nearly exclusively driven by large (skull length > 1000 mm) and carnivorous species in all studied archosauromorph groups, but particularly prominently in theropod dinosaurs. While circular orbit shapes are retained in most herbivores and smaller species, as well as in juveniles and early ontogenetic stages, large carnivores adopted elliptical and keyhole-shaped orbits. Biomechanical modelling using finite element analysis reveals that these morphologies are beneficial in mitigating and dissipating feeding-induced stresses without additional reinforcement of the bony structure of the skull.
... The feeding apparatus of extant crocodylians produces the highest measured bite forces among extant tetrapods (Erickson et al., 2003). Counter-intuitively, crocodylians do not display the typical morphology of other hard-biting tetrapods such as tegu lizards, hyenas or Tyrannosaurus, in which the skull is dorsally heightened, expanding the attachment area of temporal muscles and resisting dorsoventral bending of the rostrum (Molnar, 1998;Metzger and Herrel, 2005;Tseng and Stynder, 2011;Schaerlaeken et al., 2012). Instead, crocodylians evolved a dorsoventrally flattened skull, which is hypothesized to be an adaptation for aquatic ambush predation (Iordansky, 1973). ...
Article
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Three-dimensional computational modeling offers tools with which to investigate forces experienced by the skull encountered during feeding and other behaviors. American alligators (Alligator mississippiensis) generate some of the highest measured bite forces among extant tetrapods. A concomitant increase in bite force accompanies ontogenetic increases in body mass, which has been linked with dietary changes as animals increase in size. Because the flattened skull of crocodylians has substantial mediolaterally-oriented muscles, they are an excellent model taxon in which to explore the role of mediolateral force components experienced by the feeding apparatus. Many previous modeling studies of archosaur cranial function focused on planar analysis, ignoring the mediolateral aspects of cranial forces. Here we use three-dimensionally accurate anatomical data to resolve 3D muscle forces. Using dissection, imaging, and computational techniques, we developed lever and finite element models of an ontogenetic series of alligators to test the effects of size and shape on cranial loading and compared estimated bite forces to those previously measured in vivo in Alligator mississippiensis We found that modeled forces matched in vivo data well for intermediately sized individuals, and somewhat overestimated force in smaller specimens and underestimated force in larger specimens, suggesting that ontogenetically static muscular parameters and bony attachment sites alone cannot account for all the variation in bite force. Adding aponeurotic muscle attachments would likely improve force predictions, but such data are challenging to model and integrate into analyses of extant taxa and are generally unpreserved in fossils. We conclude that anatomically accurate modeling of muscles can be coupled with finite element and lever analyses to produce reliable, reasonably accurate estimate bite forces and thus both skeletal and joint loading, with known sources of error, which can be applied to extinct taxa.
... Tyrannosaurids as obligatory scavengers never gained popularity until recen1j}y, when the hypothesis was reintroduced by Horner and Lessem (1993). By and large, though, Tyrannosaurus has been considered an active predator, although the mode of attack remains controversial and includes flank bite and run (Paul 1987), opportunistic (Farlow 1994), and neck or snout crushing (Molnar 1998). The method of killing is assumed to have been the jaws, and the bite force has been variously calculated or estimated to have been 13,400 N (Rayfield et al. 2001), 6400-13,400 N (Erickson et al. 1996), or even 183,000-235,000 N (Meers 2002. ...
... As in other tyrannosaurid tooth examples with wear damage (e.g., Schubert and Ungar, 2005), the wear facet in YPM VPPU 025279 has an elliptical shape and smooth margins. Over the years various workers (e.g., Lambe, 1917;Farlow and Brinkman, 1994;Meers, 2002;Molnar, 1998;Jacobsen, 1998Jacobsen, , 2003Schubert and Ungar, 2005) interpreted these wear facets as either the result of tooth-to-tooth contact during feeding, or as tooth-to-soft-and-hard-tissue-of-the-prey contact. Schubert and Ungar (2005) proposed two independent factors (1) antemortem enamel spalling with subsequent smoothing of the tooth surface due to wear; and (2) attrition caused by the regular contact between the lingual surfaces of the maxillary teeth and labial surfaces of the dentary teeth. ...
... komodoensis, or rostral torsion (Molnar 1998;Holtz 2002).  The existence of deep punctures and furrows in Mesozoic assemblages may be the result of higher bite forces (i.e.Tyrannosaurus rex [Erickson et al. 1996]). ...
Poster
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Tooth marks attributed to Mesozoic ziphodont archosaurs have prompted many behavioral and paleoecological reconstructions. Unfortunately, few of these interpretations have been based on controlled observations of modern dental analogues, of which Varanus komodoensis, the Komodo monitor, is the most suitable. We conducted controlled feedings of Australian goat partial carcasses to eleven captive individuals. V. komodoensis extensively modifies bone surfaces of one third of all elements. The vast majority of marks were scores. Pits are present but significantly less common. Tooth punctures and furrows are rare. ‘Edge marks’, a trace unique to V. komodoensis, are produced on flat elements and processes. Striated tooth marks, or ‘denticle drags’, are evident on 25% of the modified elements, but represent less than 5% of all marks. The majority of marks display some degree of curvature. Over one third of the marks occur within parallel clusters. Mark production is a byproduct of flesh removal, and bone crushing was not observed. Scores are a consequence of apical dragging, resulting from the unique ‘medial-caudal arc’ defleshing technique utilized by V. komodoensis. Score and pit width is limited by apical width. Edge marks and denticle drags result from distal and mesial carinae contact respectively. Parallel clusters result from repetitive, and/or simultaneous crown contact during strokes. The high frequency of linear, parallel scoring in Mesozoic assemblages is very similar to our controlled assemblage. Following the V. komodoensis model, the majority of Mesozoic marks primarily indicates defleshing behavior with little evidence of bone chewing or crushing. The parallel nature of scores indicates similar, repetitive caudal defleshing strokes, but a lack of curvature implies less of a mesial ‘arc’. Differences in tooth mark characters and frequency between these analogues may also be explained by diagenesis and and inconsistency in evaluation procedures.
... Indeed, one of the key centers of deformation during normal biting is the quadrate-squamosal contact, which would have experienced large shear stresses associated with torque and asymmetrical loading during biting (Rayfield, 2005), and the presence of a minimal amount of cartilage between the quadrate and squamosal would therefore suggest that the synovial zone was rather a growth zone than a mobile one. A streptostylic quadrate in Tyrannosaurus rex (Molnar, 1991;Molnar, 1998), Nanotyrannus lancensis (Larson, 2013), Oviraptor philoceratops (Smith, 1992), Heyuannia huangi (Lü, 2005) and Dromiceiomimus brevitertius (Russell, 1972) based on the saddle joint between the quadrate and squamosal only is therefore unlikely. ...
Article
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The quadrate of reptiles and most other tetrapods plays an important morphofunctional role by allowing the articulation of the mandible with the cranium. In Theropoda, the morphology of the quadrate is particularly complex and varies importantly among different clades of non-avian theropods, therefore conferring a strong taxonomic potential. Inconsistencies in the notation and terminology used in discussions of the theropod quadrate anatomy have been noticed, including at least one instance when no less than eight different terms were given to the same structure. A standardized list of terms and notations for each quadrate anatomical entity is proposed here, with the goal of facilitating future descriptions of this important cranial bone. In addition, an overview of the literature on quadrate function and pneumaticity in non-avian theropods is presented, along with a discussion of the inferences that could be made from this research. Specifically, the quadrate of the large majority of non-avian theropods is akinetic but the diagonally oriented intercondylar sulcus of the mandibular articulation allowed both rami of the mandible to move laterally when opening the mouth in many of theropods. Pneumaticity of the quadrate is also present in most averostran clades and the pneumatic chamber—invaded by the quadrate diverticulum of the mandibular arch pneumatic system—was connected to one or several pneumatic foramina on the medial, lateral, posterior, anterior or ventral sides of the quadrate.
... Patterns of dorsal compression and ventral tension are consistent with the nasal region of the skull bending as a cantilever beam during biting. Even so, the presence of stress in the lacrimal and postorbital bars demonstrates that the skull does not act as a simple beam in the manner suggested by Molnar (2000) , because the postulated neutral axis of bending in the region occupied by the interfenestral bars does in fact experience stress. Furthermore, modelled stress patterns in the lacrimal can be correlated with bony morphology as the axis of biting-induced compressive stress lies along a thin but medially prominent ridge of bone in the T. rex lacrimal (e.g. ...
Article
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It has been suggested that the large theropod dinosaur Tyrannosaurus rex was capable of producing extremely powerful bite forces and resisting multi-directional loading generated during feeding. Contrary to this suggestion is the observation that the cranium is composed of often loosely articulated facial bones, although these bones may have performed a shock-absorption role. The structural analysis technique finite element analysis (FEA) is employed here to investigate the functional morphology and cranial mechanics of the T. rex skull. In particular, I test whether the skull is optimized for the resistance of large bi-directional feeding loads, whether mobile joints are adapted for the localized resistance of feeding-induced stress and strain, and whether mobile joints act to weaken or strengthen the skull overall. The results demonstrate that the cranium is equally adapted to resist biting or tearing forces and therefore the 'puncture-pull' feeding hypothesis is well supported. Finite-element-generated stress-strain patterns are consistent with T. rex cranial morphology: the maxilla-jugal suture provides a tensile shock-absorbing function that reduces localized tension yet 'weakens' the skull overall. Furthermore, peak compressive and shear stresses localize in the nasals rather than the fronto-parietal region as seen in Allosaurus, offering a reason why robusticity is commonplace in tyrannosaurid nasals.
... This group of large-bodied carnivorous dinosaurs, which includes Tyrannosaurus rex and its closest relatives, were the apex predators in Asia and North America during the final 20 million years of the Cretaceous, and were at the top of the food chain in these regions when a bolide impact (and perhaps other environmental changes) suddenly ended the age of non-avian dinosaurs 66 million years ago [1][2][3] . The vast majority of derived tyrannosauroids (tyrannosaurids) are characterized by deep skulls, thick teeth and large jaw muscles, features which allowed these dinosaurs to employ bite forces strong enough to crunch through the bones of even largebodied prey species [4][5][6][7] . This unusual body plan is thought to have been the key to tyrannosaurid success 8 . ...
Article
The iconic tyrannosaurids were top predators in Asia and North America during the latest Cretaceous, and most species had deep skulls that allowed them to generate extreme bite forces. Two unusual specimens of Alioramus from Mongolia seem to indicate a divergent long-snouted body plan among some derived tyrannosaurids, but the rarity and juvenile nature of these fossils leaves many questions unanswered. Here, we describe a remarkable new species of long-snouted tyrannosaurid from the Maastrichtian of southeastern China, Qianzhousaurus sinensis. Phylogenetic analysis places Qianzhousaurus with both species of Alioramus in a novel longirostrine clade, which was geographically widespread across latest Cretaceous Asia and formed an important component of terrestrial ecosystems during this time. The new specimen is approximately twice the size as both Alioramus individuals, showing that the long-snouted morphology was not a transient juvenile condition of deep-snouted species, but a characteristic of a major tyrannosaurid subgroup.
... Cranial mechanical behavior in various extant and extinct sauropsids has been modeled using different techniques (Busbey, 1995;Daniel & McHenry, 2001;Metzger et al. 2005;McHenry et al. 2006;Rayfield et al. 2007;Pierce et al. 2008;Rayfield & Milner, 2008;Moazen et al. 2009;Soons et al. 2010); in contrast, the sauropsid mandible has received little attention. Studies of sauropsid mandibular function include: free-body analyses of crocodilian, dinosaur and bird mandibles (Bock, 1966;Van Drongelen & Dullemeijer, 1982;Molnar, 1998); beam modeling of plesiosaur, crocodilian and theropod dinosaur mandibles (Taylor, 1992;Therrien et al. 2005;Porro et al. 2011); photoelastic studies of bird mandibles (Bock & Kummer, 1968) and finite element analysis (FEA) of the mandibles of Varanus, Alligator, several dinosaur taxa, and ostrich (Mazzetta et al. 2004;Moreno et al. 2008;Bell et al. 2009;Porro et al. 2011;Rayfield, 2011;Reed et al. 2011). FEA is a useful tool for understanding the mechanical behavior of geometrically and materially complex structures that cannot be adequately modeled using simpler methods. ...
Article
Forces experienced during feeding are thought to strongly influence the morphology of the vertebrate mandible; in vivo strain data are the most direct evidence for deformation of the mandible induced by these loading regimes. Although many studies have documented bone strains in the mammalian mandible, no information is available on strain magnitudes, orientations or patterns in the sauropsid lower jaw during feeding. Furthermore, strain gage experiments record the mechanical response of bone at a few locations, not across the entire mandible. In this paper, we present bone strain data recorded at various sites on the lower jaw of Alligator mississippiensis during in vivo feeding experiments. These data are used to understand how changes in loading regime associated with changes in bite location are related to changes in strain regime on the working and balancing sides of the mandible. Our results suggest that the working side mandible is bent dorsoventrally and twisted about its long-axis during biting, and the balancing side experiences primarily dorsoventral bending. Strain orientations are more variable on the working side than on the balancing side with changes in bite point and between experiments; the balancing side exhibits higher strain magnitudes. In the second part of this paper, we use principal strain orientations and magnitudes recorded in vivo to evaluate a finite element model of the alligator mandible. Our comparison demonstrates that strain orientations and mandibular deformation predicted by the model closely match in vivo results; however, absolute strain magnitudes are lower in the finite element model.
... Late Cretaceous tyrannosaurids are notable for their robustly constructed skulls and teeth (e.g. Osborn, 1905 Osborn, , 1912 Molnar, 1991 Molnar, , 2000 Abler, 1992), and tooth marks and biomechanical analyses indicate very strong bite forces and a puncture–pull biting strategy (see Erickson & Olson, 1996; Rayfield 2004). Indeed, tyrannosaurid skulls have robust jaws and thickened, fused nasals, which receive much of the stress exerted during feeding (Rayfield, 2004). ...
Article
The cranial osteology of the small theropod dinosaur Proceratosaurus from the Bathonian of Minchinhampton, England, is described in detail, based on new preparation and computed tomography (CT) scan images of the type, and only known, specimen. Proceratosaurus is an unusual theropod with markedly enlarged external nares and a cranial crest starting at the premaxillary–nasal junction. The skull is highly pneumatic, with pneumatized nasals, jugals, and maxillae, as well as a highly pneumatic braincase, featuring basisphenoid, anterior tympanic, basipterygoid, and carotid recesses. The dentition is unusual, with small premaxillary teeth and much larger lateral teeth, with a pronounced size difference of the serrations between the mesial and distal carina. The first dentary tooth is somewhat procumbent and flexed anteriorly. Phylogenetic analysis places Proceratosaurus in the Tyrannosauroidea, in a monophyletic clade Proceratosauridae, together with the Oxfordian Chinese taxon Guanlong. The Bathonian age of Proceratosaurus extends the origin of all clades of basal coelurosaurs back into the Middle Jurassic, and provides evidence for an early, Laurasia-wide, dispersal of the Tyrannosauroidea during the late Middle to Late Jurassic. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009.
... This curvature has implications for muscle morphology and action, static head support, and work of feeding in these powerful theropods (Molnar, 1973; Rayfield, 2004; Snively et al., 2006; Snively & Russell, 2007). The necks had to support and move the enlarged head skeleton and jaw adductor musculature of tyrannosaurids (Snively & Russell, 2007 ), which were capable of delivering and withstanding tremendously high bite forces (Molnar, 1973Molnar, , 2000 Meers, 2003; Rayfield, 2004; Therrien, Henderson & Ruff, 2005; Snively et al., 2006). We examine the influence of neck muscle topology and kinematics on feeding function of Tyrannosauridae . ...
Article
With multiple well-preserved specimens, tyrannosaurid dinosaurs are ideal subjects for exploring the role of the neck for feeding in an extinct amniote clade. Detailed exploration of the morphology of avian and crocodilian neck muscles grounds phylogenetic inference of musculature of tyrannosaurids. Introduced methods of kinematic and physiological inference explicate action and function of tyrannosaurid neck muscles, and the explicit method of extant behavioural interpolation (EBI) allows inference of generalized behaviours. Anteriorly originating craniocervical muscles of tyrannosaurids, and insertions of the neck dorsiflexor m. transversospinalis cervicis, were similar to those of birds, while the major respective head dorsiflexor and lateroflexor, m. transversospinalis capitis and m. longissimus capitis superficialis, resembled their homologues in crocodilians. Because the proposed inferential methods are cumulative and emphasize mutual falsification, behavioural effects of muscle function become immediately testable rather than assumed. Kinematic inference of muscle moment topology, and bracketed and unipolar inference of muscle activity, facilitate EBI of rapid gaze shifts, lateral and sagittal strikes, inertial feeding, and tearing of flesh by specific permutational actions of tyrannosaurid neck muscles. Several examples of EBI are tested further through biomechanical considerations. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 151, 759–808.
... Quantitative biomechanical methods allow functional hypotheses to be rigorously tested [135]; furthermore, placing biomechanical studies in a phylogenetic context and using independent evidence to corroborate results boosts confidence in functional interpretations [136]. Various biomechanical techniques have been applied to dinosaur mandibles in order to better understand feeding behavior [137], including: lever arm mechanics that estimate bite force and mechanical advantage [138,139]; free body analyses to predict tensile and compressive stress trajectories [140]; beam modeling [141]; and finite element analysis that predict stress, strain and deformation within the mandible142143144. Feeding studies in heterodontosaurids have been limited due to the fragmentary nature of most specimens, the exception being Heterodontosaurus for which there are well-preserved skulls. ...
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Background: Heterodontosaurids are an important but enigmatic and poorly understood early radiation of ornithischian dinosaurs. The late-surviving heterodontosaurid Fruitadens haagarorum from the Late Jurassic (early Tithonian) Morrison Formation of the western USA is represented by remains of several small (<1 metre total body length, <1 kg body mass) individuals that include well-preserved but incomplete cranial and postcranial material. Fruitadens is hypothesized to represent one of the smallest known ornithischian dinosaurs. Methodology/principal findings: We describe the cranial and postcranial anatomy of Fruitadens in detail, providing comparisons to all other known heterodontosaurid taxa. High resolution micro-CT data provides new insights into tooth replacement and the internal anatomy of the tooth-bearing bones. Moreover, we provide a preliminary functional analysis of the skull of late-surviving heterodontosaurids, discuss the implications of Fruitadens for current understanding of heterodontosaurid monophyly, and briefly review the evolution and biogeography of heterodontosaurids. Conclusions/significance: The validity of Fruitadens is supported by multiple unique characters of the dentition and hindlimb as well as a distinct character combination. Fruitadens shares highly distinctive appendicular characters with other heterodontosaurids, strengthening monophyly of the clade on the basis of the postcranium. Mandibular morphology and muscle moment arms suggest that the jaws of late-surviving heterodontosaurids, including Fruitadens, were adapted for rapid biting at large gape angles, contrasting with the jaws of the stratigraphically older Heterodontosaurus, which were better suited for strong jaw adduction at small gapes. The lack of wear facets and plesiomorphic dentition suggest that Fruitadens used orthal jaw movements and employed simple puncture-crushing to process food. In combination with its small body size, these results suggest that Fruitadens was an ecological generalist, consuming select plant material and possibly insects or other invertebrates.
... Lever arm mechanics have been used to estimate the efficiency of the feeding apparatus, including the mandible, and to differentiate between feeding strategies, i.e., jaws adapted for powerful rather than fast jaw closure (Ostrom, 1961;Mazzetta et al., 1998;Desojo and Vizcaíno, 2009). Molnar (1998) used free body and space frame analyses to predict tensile and compressive stress trajectories in the mandible of Tyrannosaurus. His analyses suggested that the anterior portion of the mandible (dentary) in Tyrannosaurus behaves as a cantilevered beam; posteriorly, tensile and compressive stresses were concentrated at the dorsal and ventral margins of the mandible. ...
Article
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. We tested hypotheses regarding the mechanical behavior of the mandible of Alligator mississippiensis by analyzing reaction forces and bending, shear, and torsional stress regimes in six models of varying complexity. Models included free body analysis using basic lever arm mechanics, 2D and 3D beam models, and three high-resolution finite element models of the Alligator mandible, incorporating, respectively, isotropic bone without sutures, anisotropic bone with sutures, and anisotropic bone with sutures and contact between the mandible and the pterygoid flange. Compared with the beam models, the Alligator finite element models exhibited less spatial variability in dorsoventral bending and sagittal shear stress, as well as lower peak values for these stresses, suggesting that Alligator mandibular morphology is in part designed to reduce these stresses during biting. However, the Alligator models exhibited greater variability in the distribution of mediolateral and torsional stresses than the beam models. Incorporating anisotropic bone material properties and sutures into the model reduced dorsoventral and torsional stresses within the mandible, but led to elevated mediolateral stresses. These mediolateral stresses were mitigated by the addition of a pterygoid-mandibular contact, suggesting important contributions from, and trade-offs between, material properties and external constraints in Alligator mandible design. Our results suggest that beam modeling does not accurately represent the mechanical behavior of the Alligator mandible, including important performance metrics such as magnitude and orientation of reaction forces, and mediolateral bending and torsional stress distributions. J.Morphol. 2011. © 2011 Wiley-Liss, Inc.
... Theropod dinosaurs display a high degree of craniomandibular morphological diversity, which can lead one to infer equally diverse feeding mechanisms, and thus feeding preferences, strategies, behaviours and ecology (Bakker 1986; Paul 1988; Henderson 2000; Barrett 2005; Barrett & Rayfield 2006). Biomechanical models have been used as a quantitative means to investigate the mechanics of feeding in theropods (Molnar 2000; Henderson 2002; Therrien et al. 2005), and such models have reached a new level of complexity with the advent of high-resolution computer modelling methods (Rayfield 2007). Such comparative biomechanical studies rely on the assumption, even though rarely explicitly stated, that the selected taxa truly represent different function types (such as 'typical' or 'specialized'), but the presence and distribution of function types across Theropoda have rarely been assessed. ...
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Despite the great diversity in theropod craniomandibular morphology, the presence and distribution of biting function types across Theropoda has rarely been assessed. A novel method of biomechanical profiling using mechanical advantage computed for each biting position along the entirety of the tooth row was applied to 41 extinct theropod taxa. Multivariate ordination on the polynomial coefficients of the profiles reveals the distribution of theropod biting performance in function space. In particular, coelophysoids are found to occupy a unique region of function space, while tetanurans have a wide but continuous function space distribution. Further, the underlying phylogenetic structure and evolution of biting performance were investigated using phylogenetic comparative methods. There is a strong phylogenetic signal in theropod biomechanical profiles, indicating that evolution of biting performance does not depart from Brownian motion evolution. Reconstructions of ancestral function space occupation conform to this pattern, but phylogenetically unexpected major shifts in function space occupation can be observed at the origins of some clades. However, uncertainties surround ancestor estimates in some of these internal nodes, so inferences on the nature of these evolutionary changes must be viewed with caution.
... For example, pneumatization of the lacrimal bone of Tyrannosaurus changes the cross-sections of its rami from being relatively flat (the primitive condition) to being circular and hollow. Although Molnar (2000) argued that the sinuses might weaken the skull of Tyrannosaurus, these shape changes would increase the second moment of area and polar moment of inertia and hence enhance bending and torsional rigidity, respectively, which, given the potential bite forces generated by Tyrannosaurus (Erickson et al., 1996;Meers, 2002), may have been important. On the other hand, in the case of the palatine sinus of Tyrannosaurus or some of the nasopharyngeal duct sinuses of crocodilians, the diverticula appear to have simply expanded because they could (Witmer, 1997a), producing almost grotesque bone shapes that, if anything, would hinder other functions, such as muscle attachment. ...
Article
The paranasal air sinuses and nasal cavities were studied along with other cephalic spaces (brain cavity, paratympanic sinuses) in certain dinosaurs via CT scanning and 3D visualization to document the anatomy and examine the contribution of the sinuses to the morphological organization of the head as a whole. Two representatives each of two dinosaur clades are compared: the theropod saurischians Majungasaurus and Tyrannosaurus and the ankylosaurian ornithischians Panoplosaurus and Euoplocephalus. Their extant archosaurian outgroups, birds and crocodilians (exemplified by ostrich and alligator), display a diversity of paranasal sinuses, yet they share only a single homologous antorbital sinus, which in birds has an important subsidiary diverticulum, the suborbital sinus. Both of the theropods had a large antorbital sinus that pneumatized many of the facial and palatal bones as well as a birdlike suborbital sinus. Given that the suborbital sinus interleaves with jaw muscles, the paranasal sinuses of at least some theropods (including birds) were actively ventilated rather than being dead-air spaces. Although many ankylosaurians have been thought to have had extensive paranasal sinuses, most of the snout is instead (and surprisingly) often occupied by a highly convoluted airway. Digital segmentation, coupled with 3D visualization and analysis, allows the positions of the sinuses to be viewed in place within both the skull and the head and then measured volumetrically. These quantitative data allow the first reliable estimates of dinosaur head mass and an assessment of the potential savings in mass afforded by the sinuses.
Article
The albertosaurines Albertosaurus sarcophagus and Gorgosaurus libratus are among the best represented tyrannosaurids, known from nearly complete growth series. These specimens provide an opportunity to study mandibular biomechanical properties and tooth morphology in order to infer changes in feeding behavior and bite force through ontogeny in tyrannosaurids. Mandibular force profiles reveal that the symphyseal region of albertosaurines is consistently stronger in bending than the middentary region, indicating that the anterior extremity of the jaws played an important role in prey capture and handling through ontogeny. The symphyseal region was better adapted to withstand torsional stresses than in most non-avian theropods, but not to the extent seen in Tyrannosaurus rex, suggesting that albertosaurine feeding behavior may have involved less bone crushing or perhaps relatively smaller prey than in T. rex. The constancy of these biomechanical properties at all known growth stages indicates that although albertosaurines maintained a similar feeding strategy through ontogeny, prey size/type had to change between juvenile and mature individuals. This ontogenetic dietary shift likely happened when individuals reached a mandibular length of ~58 cm, a size at which teeth shift from ziphodont to incrassate in shape and bite force begins to increase exponentially. The fact that large albertosaurines were capable of generating bite forces equivalent to similar-sized tyrannosaurines suggests that no significant differences in jaw closing musculature existed between the two clades and that the powerful bite of T. rex is the result of its large body size rather than of unique adaptations related to a specialized ecology.
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Isolated cranial and postcranial elements represent a new genus and species of endemic crocodilian, Volia athollandersoni, from presumed Pleistocene cave deposits of Fiji. Preliminary phylogenetic assessment indicates that it is a mekosuchine crocodylid. This material sheds further light on the Pleistocene tetrapod fauna of the southwestern Pacific islands.
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Simple, three-dimensional, digital models of the crania and mandibles of 22 pterosaurs – 13 pterodactyloids and nine non-pterodactyloids (‘rhamphorhynchoids’) – were generated to investigate gross-level mechanical aspects of the skulls as they would related to feeding behaviour such as bite force and speed of jaw motions. The key parameter was the determination of second moments of area of the mid-muzzle region and the computation of the bending moment relative to the occiput. The shorter, stockier skulls of basal ‘rhamphorhynchoids’ were the strongest for their size in terms of potential resistance to dorso-ventral bending, and this finding correlates with their robust dentitions. More derived ‘rhamphorhynchoids’ showed the start of a trend towards weaker skulls, but faster jaw adduction was interpreted to be an adaptation for the snatching of small prey. Pterodactyloids continued the trend to lengthen the skull and to reduce its cross-sectional area, resulting in less stiff skulls, but more rapid opening and closing of the jaws. Changes in the rear of the skulls and the development of coronoid eminences on the mandibles of all the pterodactyloids are correlated with the reduction in bite force and a concomitant increase in jaw closing speed.
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Theropods have fascinated both paleontologists and the general public due to their large diversity of sizes and morphologies. They also present a large variation in tooth morphologies. Previous studies have estimated the bite force of several specimens. The goal of this study is to determine if there is a correlation between the tooth size, shape and position on the skull and mandible and the bite force of these dinosaurs. Measurements were made on several theropods, including the bending strength of the teeth on the anterior-posterior and the mediolateral axes of the jaws, as well as the bending strength of the mandible, and were compared to fossil and modern Crocodylia. We observed that several bending strength maxima of the teeth trends were aligned with key areas of the mandible, and that the size, shape as well as the position of the teeth on the jaws were correlated with the bite force of both Crocodylia and theropods, which can be related to their diet and feeding habits.
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Tyrannosaurus rex was compared, in terms of estimated lever arm and extension of the jaw adductors, with Daspletosaurus torosus, Nanotyrannus lancensis, Allosaurus fragilis, and Ceratosaurus nasicornis. Daspletosaurus torosus agrees reasonably closely with T. rex in these parameters, indicating that no great differences in feeding adaptation were apparent from this data. Nanotyrannus differs more from T. rex; these differences appear to be related to the relatively lower skull of N. lancensis and suggest that N. lancensis had a less powerful bite than the other tyrannosaurids examined. The muscular arrangement in Allosaurus fragilis is basically similar to that of Tyrannosaurus rex. The adductors of A. fragilis had generally lower lever arms, suggesting a weaker bite but possibly indicating a greater gape. The lever arms of Ceratosaurus nasicornis are reasonably similar to those of the tyrannosaurids, suggesting that both had stronger bites than A. fragilis. © 2013, The Burpee Museum of Natural History. All rights reserved. © 2013 by The Burpee Museum of Natural History. All rights reserved.
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The study of dinosaurs has been experiencing a remarkable renaissance over the past few decades. Scientific understanding of dinosaur anatomy, biology, and evolution has advanced to such a degree that paleontologists often know more about 100-million-year-old dinosaurs than many species of living organisms. This book provides a contemporary review of dinosaur science intended for students, researchers, and dinosaur enthusiasts. It reviews the latest knowledge on dinosaur anatomy and phylogeny, how dinosaurs functioned as living animals, and the grand narrative of dinosaur evolution across the Mesozoic. A particular focus is on the fossil evidence and explicit methods that allow paleontologists to study dinosaurs in rigorous detail. Scientific knowledge of dinosaur biology and evolution is shifting fast, and this book aims to summarize current understanding of dinosaur science in a technical, but accessible, style, supplemented with vivid photographs and illustrations. The Topics in Paleobiology Series is published in collaboration with the Palaeontological Association, and is edited by Professor Mike Benton, University of Bristol. Books in the series provide a summary of the current state of knowledge, a trusted route into the primary literature, and will act as pointers for future directions for research. As well as volumes on individual groups, the series will also deal with topics that have a cross-cutting relevance, such as the evolution of significant ecosystems, particular key times and events in the history of life, climate change, and the application of a new techniques such as molecular palaeontology. The books are written by leading international experts and will be pitched at a level suitable for advanced undergraduates, postgraduates, and researchers in both the paleontological and biological sciences. Additional resources for this book can be found at: http://www.wiley.com/go/brusatte/dinosaurpaleobiology.
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Mesozoic tooth marks on bone surfaces directly link consumers to fossil assemblage formation. Striated tooth marks are believed to form by theropod denticle contact, and attempts have been made to identify theropod consumers by comparing these striations with denticle widths of contemporaneous taxa. The purpose of this study is to test whether ziphodont theropod consumer characteristics can be accurately identified from striated tooth marks on fossil surfaces. We had three major objectives (1) to experimentally produce striated tooth marks and explain how they form; (2) to determine whether body size characteristics are reflected in denticle widths; and (3) to determine whether denticle characters are accurately transcribed onto bone surfaces in the form of striated tooth marks. We conducted controlled feeding trials with the dental analogue Varanus komodoensis (the Komodo monitor). Goat (Capra hircus) carcasses were introduced to captive, isolated individuals. Striated tooth marks were then identified, and striation width, number, and degree of convergence were recorded for each. Denticle widths and tooth/body size characters were taken from photographs and published accounts of both theropod and V. komodoensis skeletal material, and regressions were compared among and between the two groups. Striated marks tend to be regularly striated with a variable degree of branching, and may co-occur with scores. Striation morphology directly reflects contact between the mesial carina and bone surfaces during the rostral reorientation when defleshing. Denticle width is influenced primarily by tooth size, and correlates well with body size, displaying negative allometry in both groups regardless of taxon or position. When compared, striation widths fall within or below the range of denticle widths extrapolated for similar-sized V. komodoensis individuals. Striation width is directly influenced by the orientation of the carina during feeding, and may underestimate but cannot overestimate denticle width. Although body size can theoretically be estimated solely by a striated tooth mark under ideal circumstances, many caveats should be considered. These include the influence of negative allometry across taxa and throughout ontogeny, the existence of theropods with extreme denticle widths, and the potential for striations to underestimate denticle widths. This method may be useful under specific circumstances, especially for establishing a lower limit body size for potential consumers.
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A detailed osteological description of Tyrannosaurus rex Osborn, 1905 is presented, based primarily on the most complete specimen yet collected of this taxon (FMNH PR2081, popularly known as “Sue”) but also including observations from other specimens.Skull morphology of FMNH PR2081 is largely congruent with that described for previous specimens, but new details are added. Palatal morphology of FMNH PR2081 differs slightly from that of previously-described specimens—the internal choanae are slightly larger relative to skull size, and the anterior expansion of the fused vomers is elongate. Posteriorly, the vomers pass medially for nearly the entire length of the pterygoids.High-resolution x-ray computed tomographic (CT) analysis of the skull reveals internal details not previously observed. Complex recess systems can be traced in the jugal, lacrymal, ectopterygoid, quadrate, exoccipital, supraoccipital, prootic, and basioccipital. The exoccipital recess was perforated by a small foramen on the posterodorsal surface of the paroccipital process, and may have communicated with pneumatic chambers in the atlas-axis complex. The maxillary antra were bound medially by a thin bony wall; traces of these walls in earlier CT studies of tyrannosaurid skulls may have led to the impression that these animals had bony maxillonasal turbintes. A digital endocast was constructed from these images, confirming many previous observations based on natural endocasts, but also yielding new details, such as the presence of a large and presumably pneumatic sinus in the prootic adjacent to the pathway for the maxillary-mandibular branches of the trigeminal nerve. The olfactory bulbs were very large.The postcranium is also largely congruent with previously published descriptions. The precaudal vertebral column was heavily pneumatized, with pneumatopores penetrating the centra and neural arches of all presacral vertebrae, the cervical ribs, and the anteriormost four sacral centra. Unusual structures are tentatively identified as a proatlas arch and a rib on the last presacral vertebrae, structures previously thought absent from tyrannosaurids. The “missing chevron” partially responsible for claims that FMNH PR2081 is female was actually present.The gastralia are extensively fused anteriorly, and the morphology of the anteriormost gastral segments closely resembles the only published account of a tyrannosaurid sternum. This raises several possibilities, including the complete absence of a bony sternum in tyrannosaurids.The appendicular skeleton is congruent with those of other tyrannosaurids. A slender rodlike bone may represent a partial furcula, but this is not certain. The scapulocoracoids would probably not have met at the midline, but would nonetheless have closely approached each other in articulation.Several abnormalities in the skeleton have attracted popular attention. There is no defensible evidence for bite trauma on the skull, but the rib cage does show evidence for healed fractures. Lesions on the right scapulocoracoid and humerus coincide with fractured ribs on the right cervical-dorsal transition and may indicate a single trauma to the right side of the body. The left fibula is pathological, but may not have been fractured. Two fused tail vertebrae may preserve natural molds of the tail muscles.
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Tyrannosaurid tooth measurements have been shown to be a powerful tool for systematic analyses, as well as for studies on function and evolution of theropod dentition. In this analysis, a variable not previously addressed in depth is added to the tyrannosaurid data set. The angle between the anterior and posterior carinae can be difficult to measure consistently and a method is hereby proposed through the use of a digitizer. Five tyrannosaurid genera were analyzed: Tyrannosaurus, Tarbosaurus, Albertosaurus, Daspletosaurus, and Gorgosaurus. Only in situ data were used, and therefore some of the taxa had a limited amount of information available for this analysis. The measurements were analyzed through multivariate analyses using Paleontological Statistics (PAST), version 2.06. The analyses included principal component analyses (PCAs), discriminant analyses (DAs), and canonical variates analyses (CVAs). The results of these analyses revealed that the angle between carinae contributes significantly to the variation in the tyrannosaurid tooth data set. Additionally, this variable showed a strong correlation to tooth function (and, consequently, to tooth families), rather than tooth size. The variation observed between taxa at this stage seems insufficient for systematic purposes, however additional in situ data would help improve the effectiveness of this tool.
Article
The objective of this study is to analyze how different crown morphologies and different root lengths respond to stresses generated by the bite forces of Albertosaurus sarcophagus and Tyrannosaurus rex. Six well-preserved teeth of A. sarcophagus from the Albertosaurus bonebed in Dry Island Park (southern Alberta) were selected to study their biomechanics, and T. rex teeth were included for comparison. The three-dimensional (3-D) models were obtained through computerized tomography (CT) scanning and 3-D digitizing. Finite element analyses were performed in Strand7 (R). Bite forces for Albertosaurus and Tyrannosaurus were calculated based on cranial and jaw proportions. The results were viewed with the Tresca yield criterion. The ratios of shear stresses observed along the mesio-distal versus labio-lingual axes of all models allows the identification of similar stress distribution patterns in the upper and lower jaws of Albertosaurus and the upper jaws of Tyrannosaurus, with a higher amount of shear along the mesio-distal axis occurring in the mid-maxillary teeth. The dentary teeth of Tyrannosaurus, however, show a different stress distribution pattern, with a higher amount of shear occurring along the labio-lingual axis of the mid-dentary teeth. These differences in jaw mechanics suggest that the function of teeth in the lower jaw of Tyrannosaurus shifted a few positions to compensate different proportions in the dentary that cause the anterior dentary teeth to be aligned with the largest maxillary teeth in Tyrannosaurus. These results suggest that heterodonty in these groups is different and that tooth form and function are sensitive to jaw proportions.
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Isolated cranial and postcranial elements represent a new genus and species of endemic crocodilian, Volia athollandersoni, from presumed Pleistocene cave deposits of Fiji. Preliminary phylogenetic assessment indicates that it is a mekosuchine crocodylid. This material sheds further light on the Pleistocene tetrapod fauna of the southwestern Pacific islands.
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Using three-dimensional, digitized data of the crania and maxillary teeth of seventeen theropod dinosaurs, biomechanical analysis reveals a series of interrelated correlations between the sizes, orientations, and ellipticity (narrowness) of the orbits and the inferred mechanical properties of the skull and teeth that relate to biting. A value for the sagittal bending strength of a cranium was computed at the longitudinal position of the orbit under an assumed load applied at the longitudinal position of the longest maxillary tooth. With the area of the orbit expressed as a percentage of the total lateral area of the skull, an inverse relationship was found to exist between the area of the orbit and the bending strength of the skull. Orbits with long-axis inclination angles in the range of 150° ± 15° are associated with taxa possessing small teeth and relatively weak skulls. Orbits with inclinations in the range of 95° ± 10° are associated with taxa possessing relatively strong skulls and long and/or strong teeth. In weak-skulled taxa, the long axes of the orbits are orientated at angles of not less than 45° to the mean inclination direction of the maxillary teeth. In strong-skulled taxa, the long axes of the orbits are sub-parallel to mean maxillary tooth direction. Finally, the ellipticity of the orbits are positively correlated with the strengths of skulls. It is proposed that the form of the orbital opening in theropods with strong skulls is governed by the requirements of the posterior half of the skull to resist the muscle generated forces associated with prey capture and/or dismemberment.
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Tyrannosaurus rex and other tyrannosaurid theropods exerted high bite forces, and large muscle attachments suggest that the tyrannosaurid neck was a concomitantly powerful component of the feeding apparatus. We examine accelerative and work-generating capacity (WGC) of neck muscles in adult Tyrannosaurus rex, using a 3-D vector-based method that incorporates aspects of muscle force generation, reconstruction of muscle morphology and moment arms, and rotational inertias of the head and neck. Under conservative assumptions, radial accelerations of the head by large superficial muscles (M. transversospinalis capitis, M. complexus, and M. longissimus capitis superficialis) enabled rapid gaze shifts and imparted high tangential velocities to food sufficient for inertial feeding. High WGC by these and deeper muscles under eccentric contraction indicate high efficacy for tearing flesh, especially with the head and neck in an extended posture. Sensitivity analyses suggest that assigned density of the antorbital region has substantial effects on calculated rotational inertia, and hence on the accuracy of results. However, even with high latitude for es-timation errors, the results indicate that adult T. rex could strike rapidly at prey and engage in complexly modulated inertial feeding, as seen in extant archosaurs.
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Carnivorous dinosaurs (Theropoda) such as Tyrannosaurus rex, Velociraptor mongoliensis, and Spinosaurus aegyptiacus are among the most popularly known fossil species and (perhaps together with the felid Smilodon and the synapsid Dimetrodon) represent the public’s primary vision of extinct predators. Numerous restorations of theropods engaged in mortal combat with each other or with one of the many clades of herbivorous dinosaurs are among the most common illustrations of life in the ancient past.
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Predatory theropod dinosaurs can usually be identified as such by features of their jaws, teeth, and postcrania, but different clades of these reptiles differed in their adaptations for prey handling. Inferences about theropod diets and hunting behavior based on functional morphology are sometimes supported by evidence from taphonomic associations with likely prey species, bite marks, gut contents, coprolites, and trackways. Very large theropods like Tyrannosaurus are unlikely to have been pure hunters or scavengers, and probably ate whatever meat they could easily obtain, dead or alive. Theropods were not the only dinosaur hunters, though; other kinds of large reptiles undoubtedly fed on dinosaurs as well. The taxonomic composition of dinosaurian predator-prey complexes varies as a function of time and geography, but an ecologically remarkable feature of dinosaurian faunas, as compared with terrestrial mammalian faunas, is the very large size commonly attained by both herbivorous and carnivorous dinosaurs. The K/T extinction event(s) did not end dinosaurian predation, because carnivorous birds remained prominent predators throughout the Cenozoic Era
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Theropod dinosaurs were, and mammalian carnivores are, the top predators within their respective communities. Beyond that, they seem distinct, differing markedly in body form and ancestry. Nevertheless, some of the same processes that shape mammalian predators and their communities likely were important to dinosaurian predators as well. To explore this, we compared the predatory adaptations of theropod dinosaurs and mammalian carnivores, focusing primarily on aspects of their feeding morphology (skulls, jaws, and teeth). We also examined suites of sympatric species (i.e., ecological guilds) of predatory theropods and mammals, emphasizing species richness and the distribution of body sizes within guilds. The morphological comparisons indicate reduced trophic diversity among theropods relative to carnivorans, as most or all theropods with teeth appear to have been hypercarnivorous. There are no clear analogs of felids, canids, and hyaenids among theropods. Interestingly, theropods parallel canids more so than felids in cranial proportions, and all theropods appear to have had weaker jaws than carnivorans. Given the apparent trophic similarity of theropods and their large body sizes, it was surprising to find that species richness of theropod guilds was as great as or exceeded that observed among mammalian carnivore guilds. Separation by body size appears to be slightly greater among sympatric theropods than carnivorans, but the magnitude of size difference between species is not constant in either group. We suggest that, as in modern carnivoran guilds, smaller theropod species might have adapted to the threats posed by much larger species (e.g., tyrannosaurs) by hunting in groups, feeding rapidly, and avoiding encounters whenever possible. This would have favored improved hunting skills and associated adaptations such as agility, speed, intelligence, and increased sensory awareness.
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Tyrannosaurid theropods are characterized by a generalized body plan, and all well-known taxa possess deep and robust skulls that are optimized for exerting powerful bite forces. The fragmentary Late Cretaceous Alioramus appears to deviate from this trend, but its holotype and only known specimen is incomplete and poorly described. A remarkable new tyrannosaurid specimen from the Maastrichtian (Late Cretaceous) of Mongolia, including a nearly complete and well-preserved skull and an extensive postcranium, represents a new species of Alioramus, Alioramus altai. This specimen conclusively demonstrates that Alioramus is a small, gracile, long-snouted carnivore that deviates from other tyrannosaurids in its body plan and presumably its ecological habits. As such, it increases the range of morphological diversity in one of the most familiar extinct clades. Phylogenetic analysis places Alioramus deep within the megapredatory Tyrannosauridae, and within the tyrannosaurine subclade that also includes Tarbosaurus and Tyrannosaurus. Both pneumatization and ornamentation are extreme compared with other tyrannosaurids, and the skull contains eight discrete horns. The new specimen is histologically aged at nine years old but is smaller than other tyrannosaurids of similar age. Despite its divergent cranial form, Alioramus is characterized by a similar sequence of ontogenetic changes as the megapredatory Tyrannosaurus and Albertosaurus, indicating that ontogenetic change is conservative in tyrannosaurids.
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Phylogenetic taxonomy, that component of phylogenetic systematics concerned with the verbal representation (rather than the reconstruction or estimation) of phylogenetic relationships, was developed by de Queiroz and Gauthier (1990, 1992, 1994). Under phylogenetic taxonomy, all taxon names are names of clades (i.e., an ancestor and all of that ancestor's descendants). De Queiroz and Gauthier (1990, 1992, 1994) described three possible ways of denning clade names within the phylogenetic taxonomic system: 1) node-based definitions (Figure 1.1), of the form “the most recent common ancestor of Taxon A and Taxon B, and all of that ancestor's descendants”; 2) stem-based definitions (Figure 1.2), of the form “Taxon A and all taxa sharing a more recent common ancestor with Taxon A than with Taxon B”; and 3) apomorphy-based definitions (Figure 1.3), of the form “the first taxon with derived character X and all of that ancestor's descendants.” Bryant (1994) noted that, while the first two definition types will always be stable, apomorphy-based definitions are potentially confusing if that derived character is found to occur in more than one lineage (i.e., is homoplastic). Under the phylogenetic system of taxonomy, definitions of taxon names are independent with respect to previous diagnosis (as particular character states may be found to occur in other lineages or in more inclusive clades) and composition (as particular member taxa may subsequently be found to lie outside the defined clade boundary). This paper is the initial work in an ongoing study by Holtz and Padian (1995, in preparation) to clarify the phylogenetic taxonomy of major clades of theropods and related taxa.
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Tyrannosaurids are a well-supported clade of very large predatory dinosaurs of Late Cretaceous Asiamerica. Traditional dinosaurian systematics place these animals within the infraorder Carnosauria with the other large theropods (allosaurids, megalosaurids). A new cladistic analysis indicates that the tyrannosaurs were in fact derived members of the Coelurosauria, a group of otherwise small theropods. Despite certain gross cranial similarities with the large predators of the Jurassic and Early Cretaceous, the Late Cretaceous tyrannosaurids are shown to be the sister group to ornithomimids and troodontids, which share a derived condition of the metatarsus. This clade is found to be nested within Maniraptora, which is a more inclusive taxon than previously recognized. The atrophied carpal structure found in tyrannosaurids and ornithomimids is derived from a maniraptoran condition with a large semilunate carpal, rather than from the plesiomorphic theropod morphology. The taxa “Carnosauria” and “Deinonychosauria” (Dromaeosauridae plus Troodontidae) are shown to be polyphyletic, and the Late Jurassic African form Elaphrosaurus is found to be the sister taxon to Abelisauridae rather than a primitive ornithomimosaur. Purported allosaurid-tyrannosaurid synapomorphies are seen to be largely size-related, present in the larger members of both clades, but absent in smaller members of the Tyrannosauridae. The remaining giant tetanurine theropods (Megalosaurus and Torvosaurus) were found to be progressively distant outgroups to an allosaurid-coelurosaur clade. The inclusion of the Tyrannosauridae within Maniraptora suggests a major adaptive radiation of coelurosaurs within Cretaceous Asiamerica comparable to contemporaneous radiations in various herbivorous dinosaurian clades.
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In recent years dinosaurs have captured the attention of the public at an unprecedented scale. At the heart of this resurgence in popular interest is an increased level of research activity, much of which is innovative in the field of palaeontology. For instance, whereas earlier palaeontological studies emphasized basic morphologic description and taxonomic classification, modern studies attempt to examine the role and nature of dinosaurs as living animals. More than ever before, we understand how these extinct species functioned, behaved, interacted with each other and the environment, and evolved. Nevertheless, these studies rely on certain basic building blocks of knowledge, including facts about dinosaur anatomy and taxonomic relationships. One of the purposes of this volume is to unravel some of the problems surrounding dinosaur systematics and to increase our understanding of dinosaurs as a biological species. Dinosaur Systematics presents a current overview of dinosaur systematics using various examples to explore what is a species in a dinosaur, what separates genders in dinosaurs, what morphological changes occur with maturation of a species, and what morphological variations occur within a species.
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The unarmored, hadrosaurian dinosaurs of the late Cretaceous of North America constitute an interesting group about which much has been written and many species described. A review of this literature showed many different angles of approach, and it was in part to reconcile these various descriptions and reduce them to certain comparable common factors that this monographic study was undertaken. Aside from the mere compilation of the literature of these dinosaurs, redescriptions were prepared, nearly always in the presence of the original types and such other associated material as had come to light since the species was named. The authors also undertook as complete a morphological study of the animals as the circumstances permitted, learning what they could of the mechanics of the skeleton and teeth, the musculature and integument, the nervous system and sense organs, and the probable functions of these various parts in the living animal. They further endeavored to imagine the reconstructed creatures in their appropriate environment—physical, climatic, vegetal, and animate—and to picture them and their manner of life as animate beings of a vanished age. An account of their distribution both in time and space is given, as well as a discussion of their probable phylogeny and the trend of their evolution.
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WHETHER tyrannosaurs occupied predatory or scavenging niches has been debated for nearly a century1-5. Palaeontologists have turned to the study of dental morphology to address this question, but the results have been highly disparate. Some contend that the tyrannosaur dentition was very strong and well suited for engaging and killing herbivorous dinosaurs6,7. Others posit that tyrannosaurs ate carrion, because their teeth and/or jaws would fail during struggles with prey2,3. The discovery of skeletal remains with bite marks from Tyrannosaurus rex8makes it possible to estimate, through indentation simulations on bovine ilia, the bite forces produced by T. rexduring feeding. The estimates (6,410 to 13,400 N) rival the largest bite forces determined for any taxon to date and suggest that T. rex had very strong, impact-resistant teeth. Although these data do not prove that T. rex was predominantly predacious, they indicate that its dentition could probably withstand the stresses associated with prey capture.
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If not having a sternum the Plesiosauria differ from the Crocodilia and from all the Lacertian orders of Reptiles. Serpents with limbs being as yet undiscovered, the only true Reptilia which admit of comparison with Plesiosaurs in the pectoral bones are the Chelonians. And even here, at first sight, the resemblance is not so evident as to command attention; for the shapes of the plastron-bones in embryonic Tortoises are more suggestive of the pectoral and pelvic girdles of Plesiosaurians than are the internal chelonian bones which support the limbs, since in Plesiosaurs these osteological elements are expanded shields which cover much of the abdominal surface. When, however, the embryonic pectoral arch of such a Chelonian as the Chelone mydas (fig. 1) is critically looked at, only unimportant osteological modification is needed to change its characters to those of a Plesiosaur. The chelonian coracoid bones (c) are rod-like; but their extension is entirely posterior to the articulation for the numeric: the bones approximate somewhat posteriorly, are somewhat concave on their outer margin, and terminate in cartilages of a shoe-shaped form, which are so extended inward that their toe-like terminations meet in the median line. Then, from the humeral articulation the two precoracoids (pc) extend inward towards the median line; they are inclined very slightly forward, and join either by their cartilages or intervening connective tissue. If, now, a line be drawn to join the median points of meeting of
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A study of the stance and locomotion of Tyrannosaurus was made for the mounting of the partial skeleton at the British Museum (Natural History). This shows that the posture was much more bird-like than is indicated by previous mounts, and also the tail is shorter. During walking the vertebral column was held nearly horizontal with the tail clear of the ground. The fore-limbs acted as struts to stop the body sliding forward as the animal raised its body from the resting position.
Article
We describe a new life restoration of Tyrannosaurus rex, based on a fairly complete skeleton (Museum of the Rockies [MOR] 555). From the volume of this model, we estimate the live mass of the full-sized dinosaur as approximately 6,000 kg. Because MOR 555 is a representative of the gracile morph of T. rex, the mass of the robust morph may have been substantially greater. The “indicator of athletic ability” or “strength indicator” of MOR 555 is 7.5–9.0 meter/giganewton, similar to previously reported results. The implication is that the cursorial potential of Tyrannosaurus was limited, a conclusion consistent with observed declines in sprint speed with increasing body mass in living animals, and also consistent with the tibia/femur length ratio, and the construction of the hip joint, of the dinosaur. Furthermore, mathematical models of the impact forces and decelerations that would affect a Tyrannosaurus, were it to fall while running at a high speed (20 meters/second), suggest that the animal would be killed in such an accident. We speculate that the top speed of adult individuals of this dinosaur species was about 10 meters/second.
Article
A skull and partial skeleton of a new genus and species, Monolophosaurus jiangi n.gen., n.sp., of large theropod has been recovered from the Middle Jurassic beds in the Junggar Basin of Xinjiang, China. The most striking characteristic is a crest, formed primarily by the nasal and lacrimal bones, on the midline of the skull. Several foramina connect the hollow interior of the crest with the antorbital fossa. The function of the crest is unknown, although it most likely was used for visual recognition by other members of the same species. It is difficult to make a precise taxonomic assignment in the absence of information on the appendicular skeleton, but it appears to be more closely related to Allosaurus than to other megalosaur grade theropods.
Article
The skull and mandible of the type specimen of the large pliosauroid plesiosaur Rhomaleosaurus zetlandicus from the Toarcian of England are elongate, and adapted for powerful predatory activity in water. The broadly caniniform dentition suggests that Rhomaleosaurus fed on a wide range of active prey, and forcibly dismembered larger prey by shaking and twisting them. The cranial musculature is reconstructed for the first time in plesiosaurs. It was adapted for feeding in water. Gross form, shape of constituent bones, and sutural morphology confirm adaptations to resist great bending moments arising from the action of the muscles when biting on prey. Rhomaleosaurus was a visual predator. The eyes were large. The stapes is present. Underwater olfaction was likely. The structure of the head of Rhomaleosaurus is a functional compromise between the needs to maximize structural strength and to maximize swimming and feeding efficiency. -from Author
Article
In 1987, a Sino-Canadian expedition known as the Dinosaur Project (China – Canada – Alberta – Ex Terra) discovered a large theropod skeleton in the Upper Jurassic Shishugou Formation of the Junggar Basin in northwestern China. The well-preserved skeleton lacks much of the tail and most of the arms, but is otherwise nearly complete. The new genus and species, Sinraptor dongi, represents a poorly understood stage of theropod evolution, even though a related form, Megalosaurus, was the first dinosaur described and named (by W. Buckland in 1824). Sinraptor has a large pneumatopore in the jugal, a pronounced postorbital rugosity, a relatively long intertemporal bar in which the postorbital appears very short in lateral aspect, and a pneumatic palatine. It is more advanced than Piatnitzkysaurus from Argentina, less derived than Allosaurus, and shows its strongest similarities to Yangchuanosaurus. The preorbital skull length of Sinraptor is relatively longer than in Yangchuanosaurus, but the skull is relatively lower. A specimen from Sichuan recently described as "Yangchuanosaurus" hepingensis represents a second species of Sinraptor. Sinraptor and Yangchuanosaurus are united in a new family of theropods, the Sinraptoridae.
Article
An extremely large claw bone, some 30 cm long, was found in Wealden (Lower Cretaceous) deposits in a Surrey claypit in January 1983. This led to the discovery the following month of the well-preserved skeleton of a new large theropod dinosaur. Only one other theropod specimen comprising more than a few bones had ever been found in Britain, and that discovery was more than a century ago. Indeed, no large theropod, reasonably complete, had previously been discovered in Lower Cretaceous rocks anywhere in the world. Our study so far suggests that the Surrey dinosaur was a typical large theropod in certain respects, resembling, for example Allosaurus. In several other respects, however, it differs sufficiently from all known dinosaurs to merit designation as the representative of a new species, genus and family.
Article
Adaptive explanations for the temporal fenestration in reptiles are briefly reviewed. With few possible exceptions, fenestrate appeared first in the reptiles, and have seemingly evolved independently in several different phyletic lines. The several explanations for fenestration offered by previous authors include speculations that open spaces in the skull permitted bulging of the jaw-closing muscles, and that fenestrae formed in areas of reduced stress where the presence of bone would be functionally useless. The first of these does not readily apply to initial evolutionary stages; the second is more satisfactory. Certain features of muscular attachments to bones are dealt with, and their implications applied to the fenestration problem to add another possible explanation (which need not contradict previously published suggestions). Considerations of cranial strength in tetrapod skulls led to speculations on the lack of fenestration in temnospondyls, anthracosaurs, microsaurs and cotylosaurs. Emargination of the skull roof in turtles is also discussed.
Article
Recent hypotheses about the mechanisms of adaptation of bone to impressed mechanical forces differ according to the extent to which tensile stresses are thought to be functionally important in bone. A pilot study of three anatomical regions by means of the photoelastic analogy suggests the possibility that net tension rarely exists in significantly large regions of bones during normal function. Thus the examination of two situations (opposite linear attachment of muscles to the lips of bony crests and opposite areal attachment of muscles to either side of thin bony plates) suggests that in rare cases where precise anatomical architecture is such that net tension may be present, then bone is not found; such regions consist of appropriate collagenous structures. In the third situation (opposite attachment of tendons to a sesamoid bone) where it would appear that net tension ought to exist, it is suggested that it is likely that it does not. Net tension probably occurs only in tendons running in tightly curved bony grooves: those very situations where sesamoid bones are not present.
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