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In sync? — Asymmetrical activation of the jaw adductors in lizards
S108
Abstracts / Comparative Biochemistry and Physiology, Part A 146 (2007) S107–S127
Prey capture is poorly studied in scleroglossans but it has been proposed that the majority of the scleroglossans use jaw prehension to capture prey. However, there are several reported cases of lingual prehension among scincomorphs (e. g. Zonosaurus laticaudatus, Cordylidae and Tiliqua rugosa, Scincidae). Our data suggest that Gherrosaurus major always use jaw prehension to capture prey. Thus, despite the close affinities of Cordyliforms (Gherrosauridae and Cordylidae) and Scincomorphs, different prey capture mechanisms are used within and across groups. Prey transport appears similar to that described for iguanians with typical puncture-crushing of prey and extensive modulation of prey transport kinematics in accordance to the characteristics of the food. However, Gherrosaurus major often employs a double powerstroke during the slow closing phase. This special movement has already been observed in Lialis (Gekkonidae) but not in other species of the Cordyliforms. Evidence for the presence of cranial kinesis has previously been put forward for Cordyliform lizards based on morphological data. Yet, cineradiographic recordings of Gherrosaurus show that cranial kinesis is absent in this genus. Thus, feeding mechanisms in cordyliforms appear unusually variable and need to be explored in more detail to understand the evolution of feeding behavior in the group. doi:10.1016/j.cbpa.2007.01.177
A6.4 In sync? — Asymmetrical activation of the jaw adductors in lizards
A6.5 Modelling the energy costs of bipedal running: The importance of elastic energy storage W. Sellers, (The University of Manchester, United Kingdom) Relatively simple musculoskeletal models are able to predict the metabolic energy costs of bipedal walking with surprising accuracy but these same models perform much less well when trying to predict the energy costs of running. The major difference seems to be that walking is primarily a ballistic activity with gravitational potential energy acting as the major energy store between steps, whereas efficient running requires the storage and recovery of elastic potential energy. This paper compares the predictions of a human-based bipedal model with and without elastic energy storage and also the specific effects of serial and elastic energy storage. It shows how the inclusion of elastic energy storage can greatly improves the absolute accuracy of metabolic energy cost estimations producing values within 20% of experimentally obtained values for humans. As a comparison the predictions from the non-elastic simulations can be wrong by over 500%. This improvement shows clear resonant effects and is only seen at physiologically reasonable levels of elasticity when both serial and parallel elements are included in the muscle-tendon model. Furthermore the tuned elastic model also predicts a much higher estimate of top running speed (5.8 m/s compared to 3.0 m/s for the non-elastic model). These results suggest that appropriate musculoskeletal simulations have very useful predictive power particularly in areas such as fossil behavioural reconstruction where direct experimentation is impossible. doi:10.1016/j.cbpa.2007.01.179
A. Herrel, V. Schaerlaeken, (University of Antwerp, Belgium); C. Ross, (University of Chicago, United States) Mammals are characterised by left-right asymmetries in the activation of the jaw adductors during chewing. This is associated with the typical unilateral chewing observed in many mammals. Moreover, mammals with fused symphyses recruit more transversely oriented balancing-side jaw adductor muscle force while chewing on hard foods. For other vertebrates such as lizards and turtles, jaw adductor activation patterns have been reported as being bilaterally synchronous and similar in amplitude, despite the largely unfused jaw symphysis in many taxa. Here we present data on the symmetry of muscle activation patterns in two species of lizards (Pogona vitticeps and Tupinambis merianae) that differ markedly in the degree of symphyseal fusion while feeding on a variety of food items differing in their mechanical properties. Using these data, we test whether animals with fused symphyses (P. vitticeps) have a more symmetrical recruitment of the jaw adductors than species with mobile symphyses (T. merianae). doi:10.1016/j.cbpa.2007.01.178
A6.6 The role of load carrying in the evolution of bipedal locomotion J. Watson, W. Sellers, (University of Manchester, United Kingdom); R. Payne, (Royal Veterinary College, United Kingdom); A. Chamberlain, (University of Sheffield, United Kingdom); R. Jones, (University of Salford, United Kingdom) The evolution of habitual bipedalism is still a fundamental yet unsolved question for palaeoanthropologists and carrying is a popular explanation for both the early adoption of upright walking and as a positive selection pressure once a terrestrial lifestyle had been adopted. However to support or reject this hypothesis we need quantitative data on the costs of different forms of carrying behaviour especially infant carrying since this became obligatory after evolutionary changes in the hominin foot led to loss of its grasping capabilities. In this study we tested the hypothesis that the mode of load carriage influences the energetic cost of locomotion. O2 consumption and stride length were measured in seven female participants walking at a
Abstracts / Comparative Biochemistry and Physiology, Part A 146 (2007) S107–S127
Prey capture is poorly studied in scleroglossans but it has been proposed that the majority of the scleroglossans use jaw prehension to capture prey. However, there are several reported cases of lingual prehension among scincomorphs (e. g. Zonosaurus laticaudatus, Cordylidae and Tiliqua rugosa, Scincidae). Our data suggest that Gherrosaurus major always use jaw prehension to capture prey. Thus, despite the close affinities of Cordyliforms (Gherrosauridae and Cordylidae) and Scincomorphs, different prey capture mechanisms are used within and across groups. Prey transport appears similar to that described for iguanians with typical puncture-crushing of prey and extensive modulation of prey transport kinematics in accordance to the characteristics of the food. However, Gherrosaurus major often employs a double powerstroke during the slow closing phase. This special movement has already been observed in Lialis (Gekkonidae) but not in other species of the Cordyliforms. Evidence for the presence of cranial kinesis has previously been put forward for Cordyliform lizards based on morphological data. Yet, cineradiographic recordings of Gherrosaurus show that cranial kinesis is absent in this genus. Thus, feeding mechanisms in cordyliforms appear unusually variable and need to be explored in more detail to understand the evolution of feeding behavior in the group. doi:10.1016/j.cbpa.2007.01.177
A6.4 In sync? — Asymmetrical activation of the jaw adductors in lizards
A6.5 Modelling the energy costs of bipedal running: The importance of elastic energy storage W. Sellers, (The University of Manchester, United Kingdom) Relatively simple musculoskeletal models are able to predict the metabolic energy costs of bipedal walking with surprising accuracy but these same models perform much less well when trying to predict the energy costs of running. The major difference seems to be that walking is primarily a ballistic activity with gravitational potential energy acting as the major energy store between steps, whereas efficient running requires the storage and recovery of elastic potential energy. This paper compares the predictions of a human-based bipedal model with and without elastic energy storage and also the specific effects of serial and elastic energy storage. It shows how the inclusion of elastic energy storage can greatly improves the absolute accuracy of metabolic energy cost estimations producing values within 20% of experimentally obtained values for humans. As a comparison the predictions from the non-elastic simulations can be wrong by over 500%. This improvement shows clear resonant effects and is only seen at physiologically reasonable levels of elasticity when both serial and parallel elements are included in the muscle-tendon model. Furthermore the tuned elastic model also predicts a much higher estimate of top running speed (5.8 m/s compared to 3.0 m/s for the non-elastic model). These results suggest that appropriate musculoskeletal simulations have very useful predictive power particularly in areas such as fossil behavioural reconstruction where direct experimentation is impossible. doi:10.1016/j.cbpa.2007.01.179
A. Herrel, V. Schaerlaeken, (University of Antwerp, Belgium); C. Ross, (University of Chicago, United States) Mammals are characterised by left-right asymmetries in the activation of the jaw adductors during chewing. This is associated with the typical unilateral chewing observed in many mammals. Moreover, mammals with fused symphyses recruit more transversely oriented balancing-side jaw adductor muscle force while chewing on hard foods. For other vertebrates such as lizards and turtles, jaw adductor activation patterns have been reported as being bilaterally synchronous and similar in amplitude, despite the largely unfused jaw symphysis in many taxa. Here we present data on the symmetry of muscle activation patterns in two species of lizards (Pogona vitticeps and Tupinambis merianae) that differ markedly in the degree of symphyseal fusion while feeding on a variety of food items differing in their mechanical properties. Using these data, we test whether animals with fused symphyses (P. vitticeps) have a more symmetrical recruitment of the jaw adductors than species with mobile symphyses (T. merianae). doi:10.1016/j.cbpa.2007.01.178
A6.6 The role of load carrying in the evolution of bipedal locomotion J. Watson, W. Sellers, (University of Manchester, United Kingdom); R. Payne, (Royal Veterinary College, United Kingdom); A. Chamberlain, (University of Sheffield, United Kingdom); R. Jones, (University of Salford, United Kingdom) The evolution of habitual bipedalism is still a fundamental yet unsolved question for palaeoanthropologists and carrying is a popular explanation for both the early adoption of upright walking and as a positive selection pressure once a terrestrial lifestyle had been adopted. However to support or reject this hypothesis we need quantitative data on the costs of different forms of carrying behaviour especially infant carrying since this became obligatory after evolutionary changes in the hominin foot led to loss of its grasping capabilities. In this study we tested the hypothesis that the mode of load carriage influences the energetic cost of locomotion. O2 consumption and stride length were measured in seven female participants walking at a