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Bite me: Biomechanical models of theropod mandibles and implications for feeding behavior
Abstract
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.
... In contrast, Irritator shows the third setup, in which the dorsal contact of the quadrate is positioned more posteriorly than the ventral one (in relation to the long axis of the mandible, the downward orientation of the snout mentioned above notwithstanding), as can be seen in some maniraptoriformes, e.g., Archaeopteryx (Rauhut, 2014) and Ornithomimosauria (Makovicky et al., 2004). Assuming a comparable relative position of the coronoid eminence and thus the insertions of the jaw muscles, this third arrangement of bones results in different jaw mechanisms, which likely produced a weak bite (lower mechanical advantage) in comparison to other large-bodied theropods (see Henderson, 2002;Therrien et al., 2005). This is partially because, in comparison to theropods with posteroventrally inclined or straight quadrates, the leverage for the jaw closing muscles (the input moment arm) is shortened in taxa with an anteroventrally inclined quadrate, such as spinosaurids, as the jaw joint moves closer to the insertion areas of the main jaw closing muscles. ...
... Reaching the point of maximal tension, the relaxation of the abductor muscles would reinforce the contraction speed of the adductor muscles, further supporting the hypothesis of a very rapid jaw closure. In summary, the skull morphology of Irritator indicates fast, rather than strong biting, supporting previous studies on skull strength and bite force in nonavian theropods (Henderson 2002;Therrien et al., 2005;Rayfield 2011). ...
Although originally described almost three decades ago, the holotype of Irritator challengeri from the Lower Cretaceous Romualdo Formation of Brazil still represents the most complete spinosaurid skull known to science. Here, we present a detailed description of the skull of Irritator based on digital reconstructions from medical and micro computed tomography (μCT) data. Segmentation reveals the near-complete palatal complex and braincase, an unusual morphology of the retroarticular process, a large, ventrally inclined surangular shelf and the tooth replacement pattern. The digitally reconstructed skull anatomy indicates a robust dentition, a field of binocular vision in front of the skull with an inclined snout orientation, a relatively weak but fast bite, as well as laterally spreading and rotating lower jaw rami during jaw opening. We modified an existing phylogenetic matrix of Tetanurae to account for new observations on the morphology of Irritator and analysed this using parsimony and Bayesian methods. Results support Spinosauridae as members of Megalosauroidea and recover a monophyletic Carnosauria (Megalosauroidea + Allosauroidea). Parsimony analysis recovers Monolophosaurus nested within Megalosauroidea as sister taxon to spinosaurids, but this is not supported by the Bayesian analysis. Bayesian time-calibration and evolutionary rate analysis indicate that spinosaurid evolution happened fast, despite a long ghost lineage of at least 35 million years. High evolutionary rates over a prolonged time can explain the highly derived skull morphology of spinosaurids. This study provides an in-depth look into the evolution of spinosaurid skull anatomy and refines our understanding of these specialized Mesozoic predators.
... Materials resist or dissipate stress in diverse ways, influenced by their ultrastructure or their geometry (Wainwright, 1992). The jaws of vertebrates experience both compressive and shear stresses during feeding (Therrien et al., 2005). Bills are subject to an additional constraint: being lightweight to support flight. ...
... In contrast, the relatively broad, weak bill of the moa genus Euryapteryx may have handled softer food (Attard et al., 2016). Beam theory suggests similar functions in theropod jaws that are weak mediolaterally, with high dorsoventral strength putatively indicating cutting or slashing feeding mechanisms (Therrien et al., 2005). The success of these mechanisms in birds, along with the stress resistance provided by the rhamphotheca, may have been key morphological innovations leading to modern bird diversity. ...
The field of comparative biomechanics examines how form, mechanical properties and environmental interactions shape the function of biological structures. Biomechanics has advanced by leaps and bounds as rapid technological progress opens up new research horizons. In this Review, I describe how our understanding of the avian bill, a morphologically diverse multifunctional appendage, has been transformed by employing a biomechanical perspective. Across functions from feeding to excavating hollows in trees and as a vocal apparatus, the study of the bill spans both solid and fluid biomechanics, rendering it useful to understand general principles across disciplines. The different shapes of the bill across bird species result in functional and mechanical trade-offs, thus representing a microcosm of many broader form-function questions. Using examples from diverse studies, I discuss how research into bird bills has been shaped over recent decades, and its influence on our understanding of avian ecology and evolution. Next, I examine how bill material properties and geometry influence performance in dietary and non-dietary contexts, simultaneously imposing trade-offs on other functions. Following an examination of the interactions of bills with fluids and their role as part of the vocal apparatus, I end with a discussion of the sensory biomechanics of the bill, focusing specifically on the bill-tip mechanosensory organ. With these case studies, I highlight how this burgeoning and consequential field represents a roadmap for our understanding of the function and evolution of biological structures.
... Some studies have proposed specific behaviors for abelisaurids based on the peculiar features of the caudal portion of their skull, cervical vertebrae, and ribs (e.g., hypertrophied epipophyses, low neural spines, ribs with aliform processes; O' Connor, 2007;Sampson & Witmer, 2007;Delcourt, 2018;González, Baiano & Vidal, 2021). Hence, behavioral inferences, especially as related to feeding habits and intraspecific behaviors, were tested by biomechanical analyses of the skull and/or the cervical portion of the axial skeleton (Mazzetta, Fariña & Vizcaíno, 1998;Mazzetta et al., 2009;Therrien, Henderson & Ruff, 2005;Snively et al., 2011). ...
Aucasaurus garridoi is an abelisaurid theropod from the Anacleto Formation (lower Campanian, Upper Cretaceous) of Patagonia, Argentina. The holotype of Aucasaurus garridoi includes cranial material, axial elements, and almost complete fore- and hind limbs. Here we present a detailed description of the axial skeleton of this taxon, along with some paleobiological and phylogenetic inferences. The presacral elements are somewhat fragmentary, although these show features shared with other abelisaurids. The caudal series, to date the most complete among brachyrostran abelisaurids, shows several autapomorphic features including the
presence of pneumatic recesses on the dorsal surface of the anterior caudal neural arches, a tubercle lateral to the prezygapophysis of mid caudal vertebrae, a marked protuberance on the lateral rim of the transverse process of the caudal vertebrae, and the presence of a small ligamentous scar near the anterior edge of the dorsal surface in the anteriormost caudal transverse process. The detailed study of the axial skeleton of Aucasaurus garridoi has also allowed us to identify characters that could be useful for future studies attempting to resolve the internal phylogenetic relationships of Abelisauridae. Computed tomography scans of some caudal vertebrae show pneumatic traits in neural arches and centra, and thus the first reported case for an abelisaurid taxon. Moreover, some osteological correlates of soft tissues present in Aucasaurus and other abelisaurids, especially derived brachyrostrans, underscore a previously proposed increase in axial rigidity within Abelisauridae.
... Having a deeply robust cranium and an expanded mandible allowed robust-snouted tyrannosauroids such as an adult Tyrannosaurus, Tarbosaurus, Daspletosaurus, and Gorgosaurus to resist high forces and deliver powerful bite forces to similarly sized prey (Gignac & Erickson, 2017;Hurum & Sabath, 2003;Rowe & Snively, 2021;Snively et al., 2006;Therrien et al., 2005Therrien et al., , 2021. ...
Tyrannosaurus has been an exemplar organism in feeding biomechanical analyses. An adult Tyrannosaurus could exert a bone‐splintering bite force, through expanded jaw muscles and a robust skull and teeth. While feeding function of adult Tyrannosaurus has been thoroughly studied, such analyses have yet to expand to other tyrannosauroids, especially early‐diverging tyrannosauroids ( Dilong, Proceratosaurus , and Yutyrannus ). In our analysis, we broadly assessed the cranial and feeding performance of tyrannosauroids at varying body sizes. Our sample size included small ( Proceratosaurus and Dilong ), medium‐sized ( Teratophoneus ), and large ( Tarbosaurus, Daspletosaurus , Gorgosaurus , and Yutyrannus ) tyrannosauroids, and incorporation of tyrannosaurines at different ontogenetic stages (small juvenile Tarbosaurus, Raptorex , and mid‐sized juvenile Tyrannosaurus ). We used jaw muscle force calculations and finite element analysis to comprehend the cranial performance of our tyrannosauroids. Scaled subtemporal fenestrae areas and calculated jaw muscle forces show that broad‐skulled tyrannosaurines ( Tyrannosaurus , Daspletosaurus , juvenile Tyrannosaurus , and Raptorex ) exhibited higher jaw muscle forces than other similarly sized tyrannosauroids ( Gorgosaurus, Yutyrannus , and Proceratosaurus ). The large proceratosaurid Yutyrannus exhibited lower cranial stress than most adult tyrannosaurids. This suggests that cranial structural adaptations of large tyrannosaurids maintained adequate safety factors at greater bite force, but their robust crania did not notably decrease bone stress. Similarly, juvenile tyrannosaurines experienced greater cranial stress than similarly‐sized earlier tyrannosauroids, consistent with greater adductor muscle forces in the juveniles, and with crania no more robust than in their small adult predecessors. As adult tyrannosauroid body size increased, so too did relative jaw muscle forces manifested even in juveniles of giant adults.
... For example, they were unlikely to have been obligate scavengers as their large size and the diversity of smaller, contemporaneous terrestrial carnivores (ornithosuchids, crocodylomorphs, theropods, and therapsid cynodonts) would have made carrion an unreliable exclusive food source (Carbone et al., 2011;Ezcurra et al., 2017;Martínez et al., 2013;Nesbitt et al., 2013). Regular osteophagy is unlikely for two main reasons: (i) Saurosuchus does not possess the incredibly high bite forces needed to crack bones as deployed by tyrannosaurids and modern crocodilians (Erickson et al., 2012(Erickson et al., , 2014Gignac & Erickson, 2017;Meers, 2002;Therrien et al., 2005), although small bones could have potentially been swallowed whole; (ii) Saurosuchus does not possess morphological features that typically facilitate bone cracking and shearing. For example, spotted hyenas have lower bite forces than African lions but their robust carnassial teeth and their enlarged zygomatic arches and sagittal crests for larger adductor muscle attachment areas all aid in producing the necessary tooth pressures to crack bone (Christiansen & Adolfssen, 2005;Christiansen & Wroe, 2007;Schubert et al., 2010). ...
Pseudosuchian archosaurs, reptiles more closely related to crocodylians than to birds, exhibited high morphological diversity during the Triassic and are thus associated with hypotheses of high ecological diversity during this time. One example involves basal loricatans which are non-crocodylomorph pseudosuchians traditionally known as "rauisuchians." Their large size (5-8+ m long) and morphological similarities to post-Triassic theropod dinosaurs, including dorsoventrally deep skulls and serrated dentitions, suggest basal loricatans were apex predators. However, this hypothesis does not consider functional behaviors that can influence more refined roles of predators in their environment, for example, degree of carcass utilization. Here, we apply finite element analysis to a juvenile but three-dimensionally well-preserved cranium of the basal loricatan Saurosuchus galilei to investigate its functional morphology and to compare with stress distributions from the theropod Allosaurus fragilis to assess degrees of functional convergence between Triassic and post-Triassic carnivores. We find similar stress distributions and magnitudes between the two study taxa under the same functional simulations, indicating that Saurosuchus had a somewhat strong skull and thus exhibited some degree of functional convergence with theropods. However, Saurosuchus also had a weak bite for an animal of its size (1015-1885 N) that is broadly equivalent to the bite force of modern gharials (Gavialis gangeticus). We infer that Saurosuchus potentially avoided tooth-bone interactions and consumed the softer parts of carcasses, unlike theropods and other basal loricatans. This deduced feeding mode for Saurosuchus increases the known functional diversity of basal loricatans and highlights functional differences between Triassic and post-Triassic apex predators.
... It would be extremely speculative to link this with inferred parental behaviour (or the lack of it), and dietary characteristics related to cochlear duct dimensions failed to produce significant signals (Hanson et al., 2021). Nevertheless, low-frequency hearing in baryonychines as an adaptation for detecting large prey would not corroborate with evidence of spinosaurids as predators of generally small vertebrates (Hone & Holtz Jr, 2017;Therrien et al., 2005), as shown by their relatively weak bite force for instance (Sakamoto, 2022). Indeed, small prey items were likely commonly selected and depredated by carnivorous theropods in general (Hone & Rauhut, 2010). ...
The digital reconstruction of neurocranial endocasts has elucidated the gross brain structure and potential ecological attributes of many fossil taxa, including Irritator, a spinosaurine spinosaurid from the "mid" Cretaceous (Aptian) of Brazil. With unexceptional hearing capabilities, this taxon was inferred to integrate rapid and controlled pitch-down movements of the head that perhaps aided in the predation of small and agile prey such as fish. However, the neuroanatomy of baryonychine spinosaurids remains to be described, and potentially informs on the condition of early spinosaurids. Using micro-computed tomographic scanning (μCT), we reconstruct the braincase endocasts of Baryonyx walkeri and Ceratosuchops inferodios from the Wealden Supergroup (Lower Cretaceous) of England. We show that the gross endocranial morphology is similar to other non-maniraptoriform theropods, and corroborates previous observations of overall endocranial conservatism amongst more basal theropods. Several differences of unknown taxonomic utility are noted between the pair. Baryonychine neurosensory capabilities include low-frequency hearing and unexceptional olfaction, whilst the differing morphology of the floccular lobe tentatively suggests less developed gaze stabilisation mechanisms relative to spinosaurines. Given the morphological similarities observed with other basal tetanurans, baryonychines likely possessed comparable behavioural sophistication, suggesting that the transition from terrestrial hypercarnivorous ancestors to semi-aquatic "generalists" during the evolution of Spinosauridae did not require substantial modification of the brain and sensory systems.
... In predatory mammals, the symphyseal shape indicates the feeding behaviour and cranial resistance during predation. Equidimensional symphyses resist to torsional stresses on prey capture or bone-cracking, while a longer symphysis indicates that stresses are predominantly induced by pressure made by the canine or the anteriormost teeth (Hylander, 1984;Therrien et al., 2005). If this symphyseal shape proportion is also maintained, Itasuchids can be considered generalist predators, which could retain their prey in the anterior portion of their snouts, possibly drowning terrestrial prey as an alternative to inertial feeding, also observed to extant crocodilians. ...
Crocodyliformes have a well-known worldwilde fossil record, revealing a high diversity of morphological traits, habits and being abundant in their paleofaunas. Such abundance in the fossil record is remarkable in the tetrapod fossil record in the continental sequences of Bauru Group (Brazil), in the Cretaceous of the South America. Here we describe and analyse three specimens from Bauru Group, assigned to a poorly understood crocodyliform clade: Itasuchidae. Their morphological similarity assigned them as Pepesuchus (from Turonian / Coniacian of Araçatuba Formation), Itasuchus cf. jesuinoi, and cf. Roxochampsa paulistanus (both last from Campanian to Early Maastrichtian of Presidente Prudente Formation). The phylogenetic and morphometric results corroborated the monophyly of the Itasuchidae with some variation in its content regard to prior and similar analyses (i.e. inclusion of Stolokrosuchus, Barreirosuchus and Antaeusuchus; exclusion of Caririsuchus), also pointing out to the South American itasuchid species as occupying a crocodyliform morphospace, which can imply distinct niche occupations. The Bauru Group undergoes a diversity peak of archosaurs in Upper Cretaceous, with a remarkable Crocodyliformes radiation, such as the Itasuchidae group, which probably have their most early-diverging lineages rising from Lower Cretaceous of Africa.
... This relationship has been postulated for non-avialan theropods (Powers et al., 2020) and exists in extant taxa as divergent as crocodilians (Walmsley et al., 2013) and canids (Slater et al., 2009), although seemingly not in felids (Sakamoto et al., 2010). A simple but powerful mechanical explanation for the connection between jaw length and preferred prey type arises from lever mechanics and beam theory, as applied to the tetrapod jaw apparatus (Ostrom, 1964;Bock, 1966;Thomason, 1991;Preuschoft & Witzel, 2002;Therrien, 2005;Therrien et al., 2005Therrien et al., , 2021. The bite force that can be applied to prey by a given tooth in a predator's mouth is inversely proportional to the distance between the jaw joint and the position of the tooth in question. ...
Gut contents are extremely important for inferring trophic interactions between extinct species. These are, however, very rare in the fossil record and it is not always possible to accurately identify both the carnivore and the consumed organisms. Here we describe the remains of a small fossil mammal foot preserved inside the body cavity of the holotype specimen of the small feathered dinosaur Microraptor zhaoianus. This adds to the known diversity of diet for this genus, which also consumed birds, fish, and lizards. Previous interpretations that Microraptor was an arboreal hunter of birds and adept hunter of fish are not supported. Although the various known stomach contents would be plausible prey items based on size, there is no clear evidence that any of them were predated rather than scavenged, and Microraptor likely did both and foraged in multiple habitats.
... Previous studies suggested that the most parsimonious explanation of this accumulation would be a feeding behavior (Alonso et al., 2017;Meso et al., 2021b). The skeletal patron of the abelisaurids and megaraptorids indicates these theropods were hyper-carnivorous (Therien et al., 2005;Sampson and Witmer, 2007;Snively and Russell, 2007;White et al., 2015b;White et al., 2016;Delcourt, 2018), substituting large carcharodontosaurids in their ecological niche. In this sense, the presence of the three teeth in association with the remains of the titanosaur Bonitasaura salgadoi suggests that South American abelisaurids and megaraptorids could fed on titanosaur sauropods. ...
The abundant record of theropods from Bajo de La Carpa Formation (Neuquén Group, Santonian), known from the end of the nineteenth century, come from numerous locations within the Neuquén Basin. During the excavation of the titanosaur Bonitasaura salgadoi at the La Bonita fossiliferous site, northwest of Río Negro province Argentina, were recovered three isolated teeth assignable to non-avian theropod dinosaurs. Previous studies of these dental materials suggested that MPCA-Pv-247 corresponds to an indeterminate tetanure possibly related to Orkoraptor, a taxon of uncertain phylogenetic position at that moment, and MPCA-Pv-249 and 251 as possible abelisauroids. Three methods were carried out, namely, a cladistic analysis performed on a dentition-based data matrix, and a discriminant and cluster analyses performed in a large dataset including measurements of non-avian theropod teeth. The results assign for the first time a confidently phylogenetic position to the described dental material. The analysis shows that MPCA-Pv 247 belongs to Megaraptoridae, whereas MPCA-Pv 249 and 251 were recovered as belonging to Abelisauridae, supporting in a reliable way the previous assignments. The results show the presence of Megaraptoridae at La Bonita and, additionally, they represent an evidence of the first direct association of megaraptorids and abelisaurids at the same locality of the Bajo de La Carpa Formation, according to similar associations from other units of the Neuquén Group.
... In addition to deep maxillae, robust maxillary and mandibular features would have also been beneficial in handling larger vertebrate prey items. Achillobator and Dromaeosaurus show a robust maxilla morphology (Currie, 1995;Perle et al., 1999) and the latter has been interpreted to have a more powerful, high efficiency bite than other dromaeosaurids (Therrien et al., 2005;Sakamoto, 2010). Although the snout dimensions for Dromaeosaurus could not be confidently estimated, estimates for Achillobator are in the mid-range of snout dimensions (L/H = 1.94), deeper than the non-estimated value of 2.22 used by Powers et al. (2020). ...
Eudromaeosauria is a clade of derived dromaeosaurids that typifies the common perception of ‘raptor’ dinosaurs. The evolutionary history of this clade has been controversial due to conflicting views of taxonomic identity, and because, due to taphonomic bias, several species were diagnosed primarily or solely by the maxilla. The maxilla is therefore crucial in understanding the phylogenetic relationships within the clade. Morphometric characterization has been commonly applied to recognize and distinguish major dromaeosaurid clades. However, morphometrics mainly showed morphological convergence rather than phylogenetic relationships. This approach has made it difficult to get resolution of phylogenetic relationships among eudromaeosaurian taxa, often resulting in large polytomies or inconsistent placement of key species. To test previous character statements, computed tomography was used to analyze the maxillae of Acheroraptor, Atrociraptor, and Deinonychus, and compare them with other eudromaeosaurians from Asia and North America. Morphometric characters were examined, and regressions were used to look for allometric trends in maxillary dimensions and the relationship to topological landmarks within Eudromaeosauria and its outgroups. Characters were improved and implemented to better capture eudromaeosaurian morphological variation and better resolve their phylogenetic relationships. Phylogenetic analysis recovered three well-defined clades within Eudromaeosauria and corroborated occurrence data within the fossil record. Acheroraptor and Atrociraptor were recovered as derived members of Saurornitholestinae. Deinonychus is recovered as a basal eudromaeosaurian, sharing features with dromaeosaurines and saurornitholestines. These results challenge previous biogeographic hypotheses suggesting Asian and North American faunal interchange during the Late Cretaceous and support convergence of traits relating to snout dimensions and proportions.
We describe the osteology of the new small theropod dinosaur Masiakasaurus knopfleri, from the Late Cretaceous Maevarano Formation of northwestern Madagascar. Approximately 40% of the skeleton is known, including parts of the jaws, axial column, forelimb, pelvic girdle, and hind limb. The jaws of Masiakasaurus are remarkably derived, bearing a heterodont, procumbent dentition that is unknown elsewhere among dinosaurs. The vertebrae are similar to those of abelisauroids in the reduction of the neural spine, lack of pleurocoelous fossae on the centrum, and extensively pneumatized neural arch. The limb skeleton is relatively gracile and bears numerous abelisauroid synapomorphies, including a rounded humeral head, peg-and-socket iliac-pubic articulation, prominent femoral medial epicondyle, expanded tibial cnemial crest, and double-grooved pedal unguals. The femora and tibiae show evidence of dimorphism. More specific features shared between Masiakasaurus, the Argentine Noasaurus, and the Indian Laevisuchus suggest that these taxa form a clade (Noasauridae) within Abelisauroidea. This is supported by a cladistic phylogenetic analysis of 158 characters and 23 theropod taxa. Additionally, Ceratosauria is rendered paraphyletic in favor of a sister-taxon relationship between Neoceratosauria and Tetanurae that is exclusive of Coelophysoidea. The unique dental and jaw specializations of Masiakasaurus suggest deviation from the typical theropod diet. Finally, the distribution of noasaurids further supports a shared biogeographic history between South America, Madagascar, and India into the Late Cretaceous.
Individual variation for the large theropod Tyrannosaurus rex may be seen in the maxilla, dentary and ischium. The maxilla is variable in its depth, the size and shape of the maxillary and antorbital fenestrae, and the size and shape of the lacrimal and jugal processes. Even the left and right maxillae of the same skull show variation. Sexual dimorphism is suggested by the presence of two morphs, one more robust than the other. The angle between the ischia and caudals of the robust morph is greater than in the slender morph, and would provide ample space for the passage of eggs. On this basis, the robust morph is considered the female. -Author
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.
Organisms must contend with the physical characteristics of their environment as they carry out a wide range of physiological and mechanical functions. Particular structural solutions must be evolved to meet particular biological demands, both within and external to theorganism. The application of engineering principles to living (and fossil) organisms, and to the materials of which they are built, represents an important interdisciplinary approach that can facilitate and help to open new insights into our understanding of organismal design and function. An understanding of this relationship is also important in terms of how organisms respond and adapt to changes in their physical environment. Although biomechanics has seen a recent growth in a number of fields within the biological sciences, the approach has had a long history (1, 2).
