Functional Morphology of Spinosaurid dinosaurs
Introduction
The Spinosauridae (fig. I) are a family of unusual theropod dinosaurs which occurred in Europe, Africa, South-America and Asia during the Lower Cretaceous. Members of this group were generally rather large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth (Buffetaut & Ouaja, 2002). They have been recorded from the Hauterivian of England (Charig & Milner 1997) and Spain (Torcida Fernãndez et al. 1997; Ruiz-Omeñaca et al. 2005) based on isolated teeth. The best known members are Baryonyx walkeri from the Barremian of England (Charig & Milner 1997) and Portugal (Buffetaut 2007) and Suchomimus tenerensis from the Aptian of Niger (Sereno et al. 1998). Irritator challengeri is represented by an incomplete but well preserved skull discovered in the Santana Formation (Albian) of Brazil (Martill et al. 1996; Sues et al. 2002) such as Angaturama limai only known from an anterior portion of the skull (Kellner & Campos 1996) that may belong to the same specimen as Irritator (Buffetaut & Ouaja 2002). Finally, Spinosaurus aegyptiacus (Stromer 1915) and the controversial species Spinosaurus marrocanus (Russell 1996) are only know from vertebrae and skull material from the Albian to the Cenomanian of North Africa (Stromer 1915; Buffetaut 1989; Russell 1996; Taquet & Russell 1998; Buffetaut & Ouaja 2002; Dal Sasso et al. 2005). Spinosaurus had a long extension of the vertebrae and was likely to have had skin connecting them, forming a sail-like structure, although Bailey (1997) has suggested that they were covered in muscle and formed a hump.
Spinosaurid dinosaurs appear to represent convergent morphological evolution toward crocodilian-like cranial morphology which has been linked to the possibility that spinosaurs fed on fish (Taquet 1984; Charig & Milner 1986, 1997; Sereno et al. 1998; Sues et al. 2002; Dal Sasso et al. 2005; Rayfield et al. 2007). Indeed, spinosaurid dinosaurs display a suite of remarkably convergent cranial characters with crown group crocodylians such as a rudimentary secondary palate, sinuous jaw margin, expanded rostral terminal rosette, and reduced antorbital fenestrae (Rayfield et al. 2007). Baryonyx walkeri was the first theropod dinosaur to conclusively display evidence of a piscivorous diet consisting of acid-etched Lepidotes scales found in the stomach region of the specimen (Charig & Milner 1997). However, partly abraded juvenile Iguanodon sp. bones found in the gut cavity of Baryonyx indicate that this theropod fed small dinosaurs as well and so was not an obligate piscivore (Charig & Milner 1997). Another documented example of a spinosaurid preyed upon a pterosaur comes to the same conclusion (Buffetaut et al. 2004).
Spinosaurid (fig. I) were relatively big theropods and partial portion of Spinosaurus aegyptiacus skull found in Morocco (Dal Sasso et al. 2005) give estimations at 1.75 meters (5.74 ft) long for the skull and around 16 to 18 meters (52 to 59 ft) in length for the entire animal, although Therrien and Henderson (2007) revised body size estimate for this specimen suggesting a much shorter animal of 12.5 meters in length. Spinosaurus aegyptiacus was also a heavy animal in which the body mass have been estimated from 7 (Dal Sasso et al. 2005) to 12 tonnes (Therrien & Henderson 2007) in weight. Their body is very similar to those of other closely related theropods such as Megalosauridae (Torvosaurus) and basal Tetanurae such as Allosauridae (Allosaurus) and Carcharodontosauridae (Acrocanthosaurus). Indeed, they possessed long and robust arms fitted up with three clawed digits and they had powerful hind limb. There were undoubtedly bipedal terrestrial carnivores although it has been suggested that spinosaurids were at least occasional quadrupeds (Charig & Milner 1986; Bailey 1997). Their anatomy affords no evidence of a gait any different from that of any other theropod. Although most of palaeontologists accepts that fish formed a significant part of the diet of spinosaurid theropods, its anatomy gives no indication of any modification towards an aquatic or semi-aquatic mode of life as they had no flipper-like modifications of the limbs and they lacked the dorso-ventrally flattened skull with dorsally situated external nares typical of crocodiles (Charig & Milner 1997). Therefore, we must ask ourselves what the reasons for convergent morphological evolution toward a crocodilian-like cranial morphology are for such terrestrial predator built theropods. Morphofunctional and biomechanical studies on Spinosauridae may answer to great number of questions on their real feeding adaptation and their terrestrial behaviour. This essay aims to present and propose several researches on spinosaurid skull and limbs using several biomechanical methods that have been done on theropod dinosaurs or spinosaurid theropods themselves. The first part focalizes on skull morphology and the analysis of stress and stress within a three-dimensional reconstruction of it. It proposes also a technique to estimate the maximal bite force of Suchomimus tenerensis. The second part presents a biomechanical study on the forelimb of Spinosauridae and it mechanical advantage. Finally, the third part introduces an analysis of hind limb muscle moment arms in Suchomimus tenerensis using a three-dimensional musculoskeletal computer model.
Discussion:
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Posté par Nekarius
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I. Functional morphology of skull and bite force estimation
As it has been mentioned before, spinosaurid skull presents some morphological convergence with fish eating animals such as crocodiles and phytosaurs. However, spinosaurids possess the plesiomorphic condition of bearing a tall, narrow, domed ('oreinorostral') skull, present in theropod sister taxa. But one of the most important feature they have developed and they shared with all extant crocodylians (Brochu 2003) are the rudimentary secondary palate appearing in the rostral snout region and the reduced antorbital fenestrae (Rayfield et al. 2007). One of the first researches that may be proposed on spinosaurid skull is certainly to understand the utility of these features which have been developed in Spinosauridae during their evolution. The hypothesis, and so the aims of a biomechanical research, would be investigating the mechanical influence on cranial function of the anteorbital fenestrae and the secondary palate because these morphological characters appear to be of importance in both crocodyliform and spinosaurs functional morphology. This study has been leaded recently by Rayfield et al. (2007) using new data from computer tomography (CT) scans and Finite Element Analysis (FEA) to test the performance of the skull of the American alligator, the Indian gharial, a generalised large theropod dinosaur and the anterior part of the snout of Baryonyx walkeri. FEA offers a powerful new approach to calculate stress and strain and thus strength in complex geometric structure like skull (Rayfield et al. 2007). This technique has been done previously by Rayfield (2004, 2005), Rayfield et al. (2001) and Jenkins et al. (2002) (among others) on several theropod skulls. In this study case, the analysis were conducted with the aim of addressing (a) the resistance of each skull to bending versus torsional loading during feeding; and the structural significance of (b) the secondary palate and (c) loss of the anteorbital fenestra (Rayfield et al. 2007). In this way, Rayfield et al. tried to determine which group is the closest functional analogue to Baryonnyx walkeri between the theropod, the alligator and the gharial.
According to their results, finite element analysis reveals that torsional stress is significantly higher than bending stress in the theropod and alligator, but there is no significant difference in the gharial and Baryonyx walkeri. Removal of the palate significantly increases torsional stress in the alligator and bending stress in the gharial and B. walkeri and adding this bone to the theropod significantly decreases both bending and torsional stresses. Finally, adding an antorbital fenestra to the gharial model significantly increases both bending and torsional stresses within the snout making the skull weaker overall in all models (Rayfield et al. 2007). Their conclusions are that Baryonyx walkeri and the gharial are functionally convergent, at least in the mechanics of the rostrum and the resistance of bending and torsional feeding loads. This new information supports the suggestion that Baryonyx walkeri, and potentially the other spinosaurid dinosaurs, engaged in at least a partially piscivorous lifestyle.
Recently, Dal Sasso et al. (2005) have described a very well preserved snout of Spinosaurus aegyptiacus (MNSM V4047) from the Late Cretaceous of Morocco, revealing new information about the structure of the snout of this very large adult spinosaur (fig III). In fact, the external nares is retracted farther caudally than in other spinosaurids such as Baryonyx walkeri and is bordered exclusively by the maxilla and nasal. Moreover, the external nares of the Baryonychinae Suchomimus and Baryonyx seem to be larger than in the Spinosaurinae Spinosaurus and Irritator (fig. IV B), but their exact size and shape cannot be established because in Baryonyx and Suchomimus the rostral portion of the nasals is missing (Dal Sasso et al. 2005). The rostromedial processes of the maxillae can be compared to the rudimentary secondary palate in B. walkeri. This process is much more elongated and narrow in Spinosaurus than in Baryonyx suggesting that the secondary palate has not been reinforced during spinosaurid evolution. Furthermore nares has been considerably reduced and moved back in the snout during the evolution of these dinosaurs. Thereby, new investigation on the mechanical influence on cranial function of the spinosaurid snout, using FEA analysis should be proposed on MNSM V4047 in order to know the evolution tendencies of the morphological changes which have been occurred in Spinosauridae.
A second research that can be proposed on Spinosaurid skull is to calculate the bite force generated by the jaws when they close rapidly. Different methods have proposed to measure the bite force of several theropod dinosaurs. Meers (2002) investigated the feeding behaviour of the theropod dinosaur Tyrannosaurus rex through analysis of two variables that are critical to successful predation, bite force and prey body mass, as they scale with the size of the predator. Bite force data compiled for extant predators (crocodylians, carnivorans, chelonians and squamates) are used to establish a relationship between bite force and body mass among extant predators. These data are used to estimate the maximum potential bite force of T. rex and the relationship between maximum prey body mass and predator body mass among the same living vertebrates is used to infer the likely maximum size of prey taken by T. rex. In the case of spinosaurid theropod, it seems unlikely that bite force can be associated with body mass. Indeed, Spinosaurus aegyptiacus in which the weight has been estimated to be worth between 7 to 12 tonnes, as much as the largest theropods dinosaurs such as Tyrannosaurus, Carcharodontosaurus and Giganotosaurus, would have had thereby the same bite force than those animals. However, the skull of Spinosaurus is much more weakly-builded and narrow and such as Baryonyx walkeri does not seems to belong to a super predator (Charig & Milner 1997). Moreover, the jaw adductor musculature is obviously little developed in spinosauridae contrary to the jaw adductor musculature in Allosaurus and Tyrannosaurus rex (fig. VI). Another research on T-rex bite force was leaded by Erickson et al. (1996) who estimated the bite force thought skeletal remains with bite marks from this theropod and indentation simulation on bovine ilia (fig. VI A). Although a spinosaurid tooth has been discovered embedded in a cervical vertebrae of a pterosaur (Buffetaut et al. 2004), it seems quite difficult to proposed the same research to measure spinosaurids bite force using bones like those of pterosaurs which are well-known to be hollow and then very weak. Furthermore, no spinosaurid skull cast such as the Suchomimus one (fig. VI B), has not enough accuracy to be used in such bite force simulation. Finally, FEA model has been applied on the skull of the large carnivorous theropod dinosaur Allosaurus fragilis (Rayfield et al. 2001; Rayfield 2005; fig. V), Carnotaurus sastrei (Mazzetta et al. 2004a) and Giganotosaurus carolinii (Mazzetta et al. 2004b) to test its mechanical properties and examine, in a quantitative way, long-held hypotheses concerning overall shape and function. Computer tomography (CT) scans has been used to generate accurate three-dimensional images of the skull forming the basis of an accurate FEA model. This model has been loaded in order to simulate different modes of biting and then calculate a bite force.
None spinosaurid skull is completely preserved and no one has been found in a "3D" position. However, Suchomimus skull cast (fig. VI B) has been reconstructed entirely, using morphology of the other spinosaurid skull. None studies using FEA model has been done on animal cast yet. It probably results from the fact that the previous studies have been focalized mainly on very-well preserved skull such those of Tyrannosaurus rex and Allosaurus fragilis rather than skull casts. Casts actually based on badly preserved skull give results with less precision and accuracy than a true skull (which has not been deformed in rocks). Moreover, bone connections inside the skull can not copy those in a skull with perfect accuracy and precision. Therefore, it seems currently impossible to measure bite force in Spinosaurid dinosaurs using current spinosaurid skull materials or cast reconstruction.
As it has been mentioned before, spinosaurid skull presents some morphological convergence with fish eating animals such as crocodiles and phytosaurs. However, spinosaurids possess the plesiomorphic condition of bearing a tall, narrow, domed ('oreinorostral') skull, present in theropod sister taxa. But one of the most important feature they have developed and they shared with all extant crocodylians (Brochu 2003) are the rudimentary secondary palate appearing in the rostral snout region and the reduced antorbital fenestrae (Rayfield et al. 2007). One of the first researches that may be proposed on spinosaurid skull is certainly to understand the utility of these features which have been developed in Spinosauridae during their evolution. The hypothesis, and so the aims of a biomechanical research, would be investigating the mechanical influence on cranial function of the anteorbital fenestrae and the secondary palate because these morphological characters appear to be of importance in both crocodyliform and spinosaurs functional morphology. This study has been leaded recently by Rayfield et al. (2007) using new data from computer tomography (CT) scans and Finite Element Analysis (FEA) to test the performance of the skull of the American alligator, the Indian gharial, a generalised large theropod dinosaur and the anterior part of the snout of Baryonyx walkeri. FEA offers a powerful new approach to calculate stress and strain and thus strength in complex geometric structure like skull (Rayfield et al. 2007). This technique has been done previously by Rayfield (2004, 2005), Rayfield et al. (2001) and Jenkins et al. (2002) (among others) on several theropod skulls. In this study case, the analysis were conducted with the aim of addressing (a) the resistance of each skull to bending versus torsional loading during feeding; and the structural significance of (b) the secondary palate and (c) loss of the anteorbital fenestra (Rayfield et al. 2007). In this way, Rayfield et al. tried to determine which group is the closest functional analogue to Baryonnyx walkeri between the theropod, the alligator and the gharial.
According to their results, finite element analysis reveals that torsional stress is significantly higher than bending stress in the theropod and alligator, but there is no significant difference in the gharial and Baryonyx walkeri. Removal of the palate significantly increases torsional stress in the alligator and bending stress in the gharial and B. walkeri and adding this bone to the theropod significantly decreases both bending and torsional stresses. Finally, adding an antorbital fenestra to the gharial model significantly increases both bending and torsional stresses within the snout making the skull weaker overall in all models (Rayfield et al. 2007). Their conclusions are that Baryonyx walkeri and the gharial are functionally convergent, at least in the mechanics of the rostrum and the resistance of bending and torsional feeding loads. This new information supports the suggestion that Baryonyx walkeri, and potentially the other spinosaurid dinosaurs, engaged in at least a partially piscivorous lifestyle.
Recently, Dal Sasso et al. (2005) have described a very well preserved snout of Spinosaurus aegyptiacus (MNSM V4047) from the Late Cretaceous of Morocco, revealing new information about the structure of the snout of this very large adult spinosaur (fig III). In fact, the external nares is retracted farther caudally than in other spinosaurids such as Baryonyx walkeri and is bordered exclusively by the maxilla and nasal. Moreover, the external nares of the Baryonychinae Suchomimus and Baryonyx seem to be larger than in the Spinosaurinae Spinosaurus and Irritator (fig. IV B), but their exact size and shape cannot be established because in Baryonyx and Suchomimus the rostral portion of the nasals is missing (Dal Sasso et al. 2005). The rostromedial processes of the maxillae can be compared to the rudimentary secondary palate in B. walkeri. This process is much more elongated and narrow in Spinosaurus than in Baryonyx suggesting that the secondary palate has not been reinforced during spinosaurid evolution. Furthermore nares has been considerably reduced and moved back in the snout during the evolution of these dinosaurs. Thereby, new investigation on the mechanical influence on cranial function of the spinosaurid snout, using FEA analysis should be proposed on MNSM V4047 in order to know the evolution tendencies of the morphological changes which have been occurred in Spinosauridae.
A second research that can be proposed on Spinosaurid skull is to calculate the bite force generated by the jaws when they close rapidly. Different methods have proposed to measure the bite force of several theropod dinosaurs. Meers (2002) investigated the feeding behaviour of the theropod dinosaur Tyrannosaurus rex through analysis of two variables that are critical to successful predation, bite force and prey body mass, as they scale with the size of the predator. Bite force data compiled for extant predators (crocodylians, carnivorans, chelonians and squamates) are used to establish a relationship between bite force and body mass among extant predators. These data are used to estimate the maximum potential bite force of T. rex and the relationship between maximum prey body mass and predator body mass among the same living vertebrates is used to infer the likely maximum size of prey taken by T. rex. In the case of spinosaurid theropod, it seems unlikely that bite force can be associated with body mass. Indeed, Spinosaurus aegyptiacus in which the weight has been estimated to be worth between 7 to 12 tonnes, as much as the largest theropods dinosaurs such as Tyrannosaurus, Carcharodontosaurus and Giganotosaurus, would have had thereby the same bite force than those animals. However, the skull of Spinosaurus is much more weakly-builded and narrow and such as Baryonyx walkeri does not seems to belong to a super predator (Charig & Milner 1997). Moreover, the jaw adductor musculature is obviously little developed in spinosauridae contrary to the jaw adductor musculature in Allosaurus and Tyrannosaurus rex (fig. VI). Another research on T-rex bite force was leaded by Erickson et al. (1996) who estimated the bite force thought skeletal remains with bite marks from this theropod and indentation simulation on bovine ilia (fig. VI A). Although a spinosaurid tooth has been discovered embedded in a cervical vertebrae of a pterosaur (Buffetaut et al. 2004), it seems quite difficult to proposed the same research to measure spinosaurids bite force using bones like those of pterosaurs which are well-known to be hollow and then very weak. Furthermore, no spinosaurid skull cast such as the Suchomimus one (fig. VI B), has not enough accuracy to be used in such bite force simulation. Finally, FEA model has been applied on the skull of the large carnivorous theropod dinosaur Allosaurus fragilis (Rayfield et al. 2001; Rayfield 2005; fig. V), Carnotaurus sastrei (Mazzetta et al. 2004a) and Giganotosaurus carolinii (Mazzetta et al. 2004b) to test its mechanical properties and examine, in a quantitative way, long-held hypotheses concerning overall shape and function. Computer tomography (CT) scans has been used to generate accurate three-dimensional images of the skull forming the basis of an accurate FEA model. This model has been loaded in order to simulate different modes of biting and then calculate a bite force.
None spinosaurid skull is completely preserved and no one has been found in a "3D" position. However, Suchomimus skull cast (fig. VI B) has been reconstructed entirely, using morphology of the other spinosaurid skull. None studies using FEA model has been done on animal cast yet. It probably results from the fact that the previous studies have been focalized mainly on very-well preserved skull such those of Tyrannosaurus rex and Allosaurus fragilis rather than skull casts. Casts actually based on badly preserved skull give results with less precision and accuracy than a true skull (which has not been deformed in rocks). Moreover, bone connections inside the skull can not copy those in a skull with perfect accuracy and precision. Therefore, it seems currently impossible to measure bite force in Spinosaurid dinosaurs using current spinosaurid skull materials or cast reconstruction.
Posté par Nekarius
II. Functional morphology of forelimbs
The spinosaurid are an intriguing group of theropod dinosaurs because they have robust forelimbs that posses a huge ungual claw. Several functions have been suggested for the forelimbs of Baryonyx walkeri; catching fish (Charig & Milner 1996; Milner 1996, 1997), offence and/or defence like a predator (Charig & Milner 1996; Milner 1997) and locomotion (Charig & Milner 1996). Charig & Milner (1997) noted that "The characters of the fore-limb and manus suggest that the forelimbs of Baryonyx were exceptionally powerful, the fore-arm being capable of exerting great force at the wrist when extended. By activating the enormous claw on the thumb, this would have enabled the animal not only to catch and kill its prey (if necessary), but also to rip and tear it to pieces". They wrote also that the enlarged claws could also have been used for gaffing, hooking or flipping fishes out of the water. A biomechanical study may determine the mechanical advantage of the forelimbs of Spinosauridae and their possible function. This research as been proposed by Benton, Kriwet and Sereno as part of an Msc project to Christine Lipkin (2003) who studied the myology and biomechanics of the forelimbs of Baryonychinae (no forelimb element has been found in Spinosaurinae yet). This former student used the work of Carpenter & Smith (2001) on the forelimb osteology and biomechanics of Tyrannosaurus rex. This research was one of the first study to test theropod forelimb biomechanics using several biomechanical analyses to determine the possible usage of the forelimbs of T. rex. First, these authors determined which mechanical system best represents the forelimb dynamics, force based (FBS) or velocity-based (VBS). They used and defined two forces, the motive force arm (MFA) and the resistive force arm as the distance from the fulcrum (pivot point) to the line of action (MA or RF). The measurements of these two forces are taken from the ulna. Secondly, they determined the power of the forelimb using the cross-sectional area of the tendon which is measured based on the size of the scare on the radius and ulna at the insertion point of the biceps muscle (Lipkin 2003). Lipkin (2003) applied these methods on Suchomimus and Baryonyx forelimbs and got results for mechanical advantage and power analysis of these two spinosaurid theropods. The interpretation from the results of the myological and biomechanical studies of Lipkin (2003) suggests that Baryonyx and Suchomimus had strong, powerful forelimbs and that Spinosauridae have a great velocity ration, which indicates a slower, more powerful movement. Consequently to these results, it has been assumed that the spinosaurids were piscivorous and could use their forelimbs for gaffing fish out of water. Their mighty forelimbs reveal that they may have also been active terrestrial predators that also scavenged and that they were bipedal and could use their forelimbs for occasional quadrupedal locomotion (Lipkin 2003).
Another kind of research on spinosaurids forelimbs based on Senter and Robins (2004) studies on Acrocanthosaurus atokensis can be proposed as well. Casts of forelimb elements of this Cretaceous theropod dinosaur were manually manipulated to determine range of motion and infer function. Thereby, it was found that the humerus can swing posteriorly into a horizontal position but can neither swing laterally to glenoid height nor anteriorly much beyond the glenoid. The forearm can approach but not achieve full extension and right-angle flexion. Pronation and supination are precluded by immobility of the radius relative to the ulna. Motion also seems to be restricted at the wrist. The palm faces medially, and digital movement is subtransverse. All three digits are capable of extreme hyper-extension. This kind of research which used casts element seem to be much more easier and much more accurate than those on biomechanics of T-rex forelimbs proposed by Carpenter & Smith (2001). Several hypotheses can be proposed in Baryonychinae forelimbs such as similar movements like Acrocanthosaurus atokensis in the humerus, the radius and the ulna. However, it is quite hard to formulate any conclusion concerning the Baryonychinae forelimbs movements without any deep research using casts of forelimb element.
The spinosaurid are an intriguing group of theropod dinosaurs because they have robust forelimbs that posses a huge ungual claw. Several functions have been suggested for the forelimbs of Baryonyx walkeri; catching fish (Charig & Milner 1996; Milner 1996, 1997), offence and/or defence like a predator (Charig & Milner 1996; Milner 1997) and locomotion (Charig & Milner 1996). Charig & Milner (1997) noted that "The characters of the fore-limb and manus suggest that the forelimbs of Baryonyx were exceptionally powerful, the fore-arm being capable of exerting great force at the wrist when extended. By activating the enormous claw on the thumb, this would have enabled the animal not only to catch and kill its prey (if necessary), but also to rip and tear it to pieces". They wrote also that the enlarged claws could also have been used for gaffing, hooking or flipping fishes out of the water. A biomechanical study may determine the mechanical advantage of the forelimbs of Spinosauridae and their possible function. This research as been proposed by Benton, Kriwet and Sereno as part of an Msc project to Christine Lipkin (2003) who studied the myology and biomechanics of the forelimbs of Baryonychinae (no forelimb element has been found in Spinosaurinae yet). This former student used the work of Carpenter & Smith (2001) on the forelimb osteology and biomechanics of Tyrannosaurus rex. This research was one of the first study to test theropod forelimb biomechanics using several biomechanical analyses to determine the possible usage of the forelimbs of T. rex. First, these authors determined which mechanical system best represents the forelimb dynamics, force based (FBS) or velocity-based (VBS). They used and defined two forces, the motive force arm (MFA) and the resistive force arm as the distance from the fulcrum (pivot point) to the line of action (MA or RF). The measurements of these two forces are taken from the ulna. Secondly, they determined the power of the forelimb using the cross-sectional area of the tendon which is measured based on the size of the scare on the radius and ulna at the insertion point of the biceps muscle (Lipkin 2003). Lipkin (2003) applied these methods on Suchomimus and Baryonyx forelimbs and got results for mechanical advantage and power analysis of these two spinosaurid theropods. The interpretation from the results of the myological and biomechanical studies of Lipkin (2003) suggests that Baryonyx and Suchomimus had strong, powerful forelimbs and that Spinosauridae have a great velocity ration, which indicates a slower, more powerful movement. Consequently to these results, it has been assumed that the spinosaurids were piscivorous and could use their forelimbs for gaffing fish out of water. Their mighty forelimbs reveal that they may have also been active terrestrial predators that also scavenged and that they were bipedal and could use their forelimbs for occasional quadrupedal locomotion (Lipkin 2003).
Another kind of research on spinosaurids forelimbs based on Senter and Robins (2004) studies on Acrocanthosaurus atokensis can be proposed as well. Casts of forelimb elements of this Cretaceous theropod dinosaur were manually manipulated to determine range of motion and infer function. Thereby, it was found that the humerus can swing posteriorly into a horizontal position but can neither swing laterally to glenoid height nor anteriorly much beyond the glenoid. The forearm can approach but not achieve full extension and right-angle flexion. Pronation and supination are precluded by immobility of the radius relative to the ulna. Motion also seems to be restricted at the wrist. The palm faces medially, and digital movement is subtransverse. All three digits are capable of extreme hyper-extension. This kind of research which used casts element seem to be much more easier and much more accurate than those on biomechanics of T-rex forelimbs proposed by Carpenter & Smith (2001). Several hypotheses can be proposed in Baryonychinae forelimbs such as similar movements like Acrocanthosaurus atokensis in the humerus, the radius and the ulna. However, it is quite hard to formulate any conclusion concerning the Baryonychinae forelimbs movements without any deep research using casts of forelimb element.
Posté par Nekarius
III. Functional morphology of hind limbs
Spinosaurid hind limbs do not differ greatly from their closely related cousins such as Torvosaurus, and Allosaurus. No research on Spinosaurid hind limbs has been done yet up to now. In fact, only the hind limb elements of Suchomimus tenerensis seem to be present and correctly preserved (Sereno et al. 1998). Indeed, hind limb bones of Baryonyx walkeri, and particularly the femur, suffered extreme damage from clay-winning operations before the presence of the dinosaur skeleton was recognized. Only the fibula and the calcaneum are in good condition (Charig & Milner 1997). The Metatarsals, tarsals and most of the digits of Suchomimus are missing with the result that no accurate research on functional morphology of the entire hind limbs of Suchomimus tenerensis can be proposed.
Hutchinson et al. (2005) are certainly the only ones to have deeply investigated the functional morphology of hind limb in a theropod dinosaur. They have analysed the hind limb muscle moment arms in Tyrannosaurus rex using a three-dimensional musculoskeletal computer model. The goals of this study were to (1) develop a three-dimensional graphics-based model of the musculoskeletal system of the Cretaceous theropod dinosaur Tyrannosaurus rex that predicts muscle-tendon unit paths, lengths, and moment arms for a range of limb positions; (2) use the model to determine how the T. rex hind limb muscle moment arms varied between crouched and upright poses; (3) compare the predicted moment arms with previous assessments of muscle function in dinosaurs; (4) evaluate how the magnitudes of these moment arms compare with those in other animals; and (5) integrate these findings with previous biomechanical studies to produce a revised appraisal of stance, gait, and speed in T. rex. Thereby, they digitized the pelvis, femur, tibia, fibula, astragalus, calcaneum, distal tarsals, and metatarsals II-IV. Then muscles that have the same rough positions and connections in extant archosaurs (crocodiles and birds) have been placed into a musculoskeletal model with confidence (fig. VIII). Finally, the musculoskeletal model used the ‘‘partial velocity'' method to calculate moment arms as a function of joint angle (Hutchinson et al. 2005).
Although metatarsals and digit of the pes are missing in Suchomimus, the pelvis seems to be completely preserved in this species. Thereby, it may allow to place several muscles (at least 22 muscles) connected from the ilium to the extreme distal part of the tibia and the fibula. Then, a numerous of measure can be done on muscle moment arm for each muscle allowing to observe the change in hip and hind limb muscles against joint flexion/extension angle. Several graphs such those in fig VIII may be obtained and may reveal some precious information on the mechanics of the hip and the knee. However, no conclusion can be drawn on the spinosaurids locomotion, stance and speed without the metatarsals and digits elements.
Spinosaurid hind limbs do not differ greatly from their closely related cousins such as Torvosaurus, and Allosaurus. No research on Spinosaurid hind limbs has been done yet up to now. In fact, only the hind limb elements of Suchomimus tenerensis seem to be present and correctly preserved (Sereno et al. 1998). Indeed, hind limb bones of Baryonyx walkeri, and particularly the femur, suffered extreme damage from clay-winning operations before the presence of the dinosaur skeleton was recognized. Only the fibula and the calcaneum are in good condition (Charig & Milner 1997). The Metatarsals, tarsals and most of the digits of Suchomimus are missing with the result that no accurate research on functional morphology of the entire hind limbs of Suchomimus tenerensis can be proposed.
Hutchinson et al. (2005) are certainly the only ones to have deeply investigated the functional morphology of hind limb in a theropod dinosaur. They have analysed the hind limb muscle moment arms in Tyrannosaurus rex using a three-dimensional musculoskeletal computer model. The goals of this study were to (1) develop a three-dimensional graphics-based model of the musculoskeletal system of the Cretaceous theropod dinosaur Tyrannosaurus rex that predicts muscle-tendon unit paths, lengths, and moment arms for a range of limb positions; (2) use the model to determine how the T. rex hind limb muscle moment arms varied between crouched and upright poses; (3) compare the predicted moment arms with previous assessments of muscle function in dinosaurs; (4) evaluate how the magnitudes of these moment arms compare with those in other animals; and (5) integrate these findings with previous biomechanical studies to produce a revised appraisal of stance, gait, and speed in T. rex. Thereby, they digitized the pelvis, femur, tibia, fibula, astragalus, calcaneum, distal tarsals, and metatarsals II-IV. Then muscles that have the same rough positions and connections in extant archosaurs (crocodiles and birds) have been placed into a musculoskeletal model with confidence (fig. VIII). Finally, the musculoskeletal model used the ‘‘partial velocity'' method to calculate moment arms as a function of joint angle (Hutchinson et al. 2005).
Although metatarsals and digit of the pes are missing in Suchomimus, the pelvis seems to be completely preserved in this species. Thereby, it may allow to place several muscles (at least 22 muscles) connected from the ilium to the extreme distal part of the tibia and the fibula. Then, a numerous of measure can be done on muscle moment arm for each muscle allowing to observe the change in hip and hind limb muscles against joint flexion/extension angle. Several graphs such those in fig VIII may be obtained and may reveal some precious information on the mechanics of the hip and the knee. However, no conclusion can be drawn on the spinosaurids locomotion, stance and speed without the metatarsals and digits elements.
Posté par Nekarius
Conclusions
Several studies of biomechanical analysis on Spinosauridae skull and limbs have been presented and proposed in this essay. Most of the research that have been done come to a same conclusion. Spinosauridae were engaged in at least a partially piscivorous lifestyle whatever the method and technique that have been used. A couple of new researches on the spinosaurid skull such as a FEA analysis on the Spinosaurus aegyptiacus snout descibed by Dal Sasso et al. (2005) and the forelimb and hind limbs of functional morphology of Suchomimus tenerensis have been proposed and would deserved attention in future biomechanics studies on Spinosauridae.
Several studies of biomechanical analysis on Spinosauridae skull and limbs have been presented and proposed in this essay. Most of the research that have been done come to a same conclusion. Spinosauridae were engaged in at least a partially piscivorous lifestyle whatever the method and technique that have been used. A couple of new researches on the spinosaurid skull such as a FEA analysis on the Spinosaurus aegyptiacus snout descibed by Dal Sasso et al. (2005) and the forelimb and hind limbs of functional morphology of Suchomimus tenerensis have been proposed and would deserved attention in future biomechanics studies on Spinosauridae.
Posté par Nekarius
Bon, il doit y avoir beaucoup de fautes d'anglais puisque j'ai écris ça hier soir en un peu plus de 12 heures (d'affilées) entre 3h30 du mat et 16h30. Et j'ai pas pu me relire, la deadline étant fixé à 17h00...
Donc désolé pour les fautes...
Donc désolé pour les fautes...
Posté par Alpic
It is not grave. I don't understand queudalle. 
Ca a l'air d'être un sacré boulot. Si tu ne sais pas quoi faire la nuit prochaine
, mets le nous en frenchy. 
Thanks boy !
Ca a l'air d'être un sacré boulot. Si tu ne sais pas quoi faire la nuit prochaine
, mets le nous en frenchy. Thanks boy !
Posté par Nekarius
Oui, je m'occuperai de la traduction dans les prochains jours.
A partir de demain, j'ai plus aucun cours jusque mai.
A part mon project sur la diversité et la disparité des Sauropodomorphes, j'ai rien à faire d'autre...
A partir de demain, j'ai plus aucun cours jusque mai.
A part mon project sur la diversité et la disparité des Sauropodomorphes, j'ai rien à faire d'autre...
Posté par Alpic
Cool la vie non ? 
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