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Tea Jashashvili - One of the best experts on this subject based on the ideXlab platform.
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
Journal of Human Evolution, 2019Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea JashashviliAbstract:Abstract Due to its completeness, the A.L. 288-1 (‘Lucy’) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus -like chimp/human last common ancestor (CLCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma ‘Little Foot’ (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. We found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus , as represented by StW 573 and A.L. 288-1, exhibit a significantly different ( p Ardipithecus and Australopithecus , followed by a considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens .
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The long Limb Bones of the StW 573 Australopithecus skeleton from Sterkfontein Member 2: Descriptions and proportions
Journal of Human Evolution, 2019Co-Authors: Jason Heaton, Travis Rayne Pickering, Tea Jashashvili, Kristian Carlson, Robin Crompton, Amélie Beaudet, Laurent Bruxelles, Kathleen Kuman, Andrea Heile, Dominic StratfordAbstract:Due to its completeness, the A.L. 288-1 (‘Lucy’) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like chimp/human last common ancestor (CLCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma ‘Little Foot’ (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. We found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, exhibit a significantly different (p < 0.001) allometric pattern than that which typifies modern humans and African apes. Like some previous analyses, our results also suggest that hominin Limb evolution occurred in two stages with: first, a modest increase in lower Limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by a considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens.
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
bioRxiv, 2018Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea Jashashvili, Amélie BeaudetAbstract:Due to its completeness, the A.L. 288-1 ("Lucy") skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like most recent common ancestor (MRCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of A. sediba (MH1 and MH2) and A. afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ~3.67 Ma "Little Foot" (StW 573) specimen, from Sterkfontein Member 2. Here, we provide the first descriptions of that skeletons upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. As to the latter, we found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1s Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, developed along a significantly different (p < 0.001) allometric scale than that which typifies modern humans and African apes. Our analyses also suggest, as have those of others, that hominin Limb evolution occurred in two stages with: (1) a modest increase in lower Limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by (2) considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens.
Kristian J Carlson - One of the best experts on this subject based on the ideXlab platform.
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
Journal of Human Evolution, 2019Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea JashashviliAbstract:Abstract Due to its completeness, the A.L. 288-1 (‘Lucy’) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus -like chimp/human last common ancestor (CLCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma ‘Little Foot’ (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. We found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus , as represented by StW 573 and A.L. 288-1, exhibit a significantly different ( p Ardipithecus and Australopithecus , followed by a considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens .
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
bioRxiv, 2018Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea Jashashvili, Amélie BeaudetAbstract:Due to its completeness, the A.L. 288-1 ("Lucy") skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like most recent common ancestor (MRCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of A. sediba (MH1 and MH2) and A. afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ~3.67 Ma "Little Foot" (StW 573) specimen, from Sterkfontein Member 2. Here, we provide the first descriptions of that skeletons upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. As to the latter, we found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1s Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, developed along a significantly different (p < 0.001) allometric scale than that which typifies modern humans and African apes. Our analyses also suggest, as have those of others, that hominin Limb evolution occurred in two stages with: (1) a modest increase in lower Limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by (2) considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens.
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locomotor variation and bending regimes of capuchin Limb Bones
American Journal of Physical Anthropology, 2009Co-Authors: Brigitte Demes, Kristian J CarlsonAbstract:Primates are very versatile in their modes of progression, yet laboratory studies typically capture only a small segment of this variation. In vivo bone strain studies in particular have been commonly constrained to linear locomotion on flat substrates, conveying the potentially biased impression of stereotypic long bone loading patterns. We here present substrate reaction forces (SRF) and Limb postures for capuchin monkeys moving on a flat substrate ("terrestrial"), on an elevated pole ("arboreal"), and performing turns. The angle between the SRF vector and longitudinal axes of the forearm or leg is taken as a proxy for the bending moment experienced by these Limb segments. In both frontal and sagittal planes, SRF vectors and distal Limb segments are not aligned, but form discrepant angles; that is, forces act on lever arms and exert bending moments. The positions of the SRF vectors suggest bending around oblique axes of these Limb segments. Overall, the leg is exposed to greater moments than the forearm. Simulated arboreal locomotion and turns introduce variation in the discrepancy angles, thus confirming that expanding the range of locomotor behaviors studied will reveal variation in long bone loading patterns that is likely characteristic of natural locomotor repertoires. "Arboreal" locomotion, even on a linear noncompliant branch, is characterized by greater variability of force directions and discrepancy angles than "terrestrial" locomotion (significant for the forearm only), partially confirming the notion that life in trees is associated with greater variation in long bone loading. Directional changes broaden the range of external bending moments even further.
Travis Rayne Pickering - One of the best experts on this subject based on the ideXlab platform.
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
Journal of Human Evolution, 2019Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea JashashviliAbstract:Abstract Due to its completeness, the A.L. 288-1 (‘Lucy’) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus -like chimp/human last common ancestor (CLCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma ‘Little Foot’ (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. We found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus , as represented by StW 573 and A.L. 288-1, exhibit a significantly different ( p Ardipithecus and Australopithecus , followed by a considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens .
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The long Limb Bones of the StW 573 Australopithecus skeleton from Sterkfontein Member 2: Descriptions and proportions
Journal of Human Evolution, 2019Co-Authors: Jason Heaton, Travis Rayne Pickering, Tea Jashashvili, Kristian Carlson, Robin Crompton, Amélie Beaudet, Laurent Bruxelles, Kathleen Kuman, Andrea Heile, Dominic StratfordAbstract:Due to its completeness, the A.L. 288-1 (‘Lucy’) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like chimp/human last common ancestor (CLCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma ‘Little Foot’ (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. We found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, exhibit a significantly different (p < 0.001) allometric pattern than that which typifies modern humans and African apes. Like some previous analyses, our results also suggest that hominin Limb evolution occurred in two stages with: first, a modest increase in lower Limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by a considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens.
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
bioRxiv, 2018Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea Jashashvili, Amélie BeaudetAbstract:Due to its completeness, the A.L. 288-1 ("Lucy") skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like most recent common ancestor (MRCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of A. sediba (MH1 and MH2) and A. afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ~3.67 Ma "Little Foot" (StW 573) specimen, from Sterkfontein Member 2. Here, we provide the first descriptions of that skeletons upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. As to the latter, we found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1s Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, developed along a significantly different (p < 0.001) allometric scale than that which typifies modern humans and African apes. Our analyses also suggest, as have those of others, that hominin Limb evolution occurred in two stages with: (1) a modest increase in lower Limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by (2) considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens.
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Success in Identification of Experimentally Fragmented Limb Bone Shafts: Implications for Estimates of Skeletal Element Abundance in Archaeofaunas
Journal of taphonomy, 2006Co-Authors: Travis Rayne Pickering, Charles P. Egeland, Amy G. Schnell, Daniel L. Osborne, Jake EnkAbstract:A strong pattern of high hindLimb representation (especially tibiae) was recognized in our survey of zooarchaeological analyses that included Limb bone shafts in estimates of element abundance in assemblages from the Old and New Worlds, from widely spread time periods and with various hominid species that acted as bone accumulators. Inter-element differences in bone mineral density and carcass transport behavior by hominids do not explain the pattern satisfactorily. We hypothesized that shaft fragments of hindLimb elements (especially tibiae) might be more ?intrinsically identifiable? than are fragments from other Limb Bones, and constructed an experiment to test this idea. Whole Limb Bones were sectioned into shaft fragments of various sizes using a bandsaw. An experienced faunal analyst (TRP), who was uninvolved in the bone selection and preparation, was required to identify the fragments as accurately as possible to specific skeletal element. Identification bouts were divided into 14 individual sorts, each consisting of 24 randomly assigned specimens. Sorts were constructed to replicate an increasing degree of communition across three stages: two ?Stage I? sorts contain large specimens, four ?Stage II? sorts contain smaller specimens and eight ?Stage III? sorts contain the smallest specimens. Refitting and guessing were not allowed and fragments identified to a non-element-specific category (i. E.: upper Limb segment, humerus or femur; intermediate Limb segment, radius or tibia; lower Limb segment, metacarpal or metatarsal; Limb bone shaft only) were not counted as a correct identification. Of 336 total specimens, 195 (58.0 %) were correctly identified to element. Overall, the differences in proportions of skeletally identified fragments for all six elements are not statistically significant. This finding seemingly falsifies the hypothesis that shaft fragments from hindLimb elements (especially tibiae) are more intrinsically identifiable than are fragments of other Limb Bones. However, our study also highlights the need for additional testing of the hypothesis since most actual archaeofaunas preserve many more specimens with complete or nearly complete diaphyseal circumference than does our experimental sample, which is composed entirely of specimens with preserving
Richard W Blob - One of the best experts on this subject based on the ideXlab platform.
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Diversity of Limb-bone safety factors for locomotion in terrestrial vertebrates: evolution and mixed chains.
Integrative and comparative biology, 2014Co-Authors: Richard W Blob, Nora R. Espinoza, Michael T. Butcher, Andrew H. Lee, Angela R. D’amico, Faraz Baig, K. Megan SheffieldAbstract:During locomotion over land, vertebrates' Limb Bones are exposed to loads. Like most biological structures, Limb Bones have a capacity to withstand greater loads than they usually experience, termed a safety factor (SF). How diverse are Limb-bone SFs, and what factors correlate with such variation? We have examined these questions from two perspectives. First, we evaluated locomotor SF for the femur in diverse lineages, including salamanders, frogs, turtles, lizards, crocodilians, and marsupials (opossums). Comparisons with values for hind-Limb elements in running birds and eutherian mammals indicate phylogenetic diversity in Limb-bone SF. A high SF (∼7) is primitive for tetrapods, but low magnitudes of load and elevated strength of Bones contribute to different degrees across lineages; moreover, birds and eutherians appear to have evolved lower SFs independently. Second, we tested the hypothesis that SFs would be similar across Limb Bones within a taxon by comparing data from the humerus and femur of alligators. Both in bending and in torsion, we found a higher SF for the humerus than for the femur. Such a "mixed chain" of different SFs across elements has been predicted if Bones have differing variabilities in load, different costs to maintain, or high SF values in general. Although variability in load is similar for the humerus and femur, a high SF may be less costly for the humerus because it is smaller than the femur. The high SFs of alligators also might facilitate differences in SF among their Limb Bones. Beyond these specific findings, however, a more general implication of our results is that evaluations of the diversity of Limb-bone SFs can provide important perspective to direct future research. In particular, more complete understanding of variation in SF could provide insight into factors that promoted the evolutionary radiation of terrestrial locomotor function in vertebrates.
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mechanics of Limb bone loading during terrestrial locomotion in the green iguana iguana iguana and american alligator alligator mississippiensis
The Journal of Experimental Biology, 2001Co-Authors: Richard W Blob, Andrew A BiewenerAbstract:In vivo measurements of strain in the femur and tibia of Iguana iguana (Linnaeus) and Alligator mississippiensis (Daudin) have indicated three ways in which Limb bone loading in these species differs from patterns observed in most birds and mammals: (i) the Limb Bones of I. iguana and A. mississippiensis experience substantial torsion, (ii) the Limb Bones of I. iguana and A. mississippiensis have higher safety factors than those of birds or mammals, and (iii) load magnitudes in the Limb Bones of A. mississippiensis do not decrease uniformly with the use of a more upright posture. To verify these patterns, and to evaluate the ground and muscle forces that produce them, we collected three-dimensional kinematic and ground reaction force data from subadult I. iguana and A. mississippiensis using a force platform and high-speed video. The results of these force/kinematic studies generally confirm the loading regimes inferred from in vivo strain measurements. The ground reaction force applies a torsional moment to the femur and tibia in both species; for the femur, this moment augments the moment applied by the caudofemoralis muscle, suggesting large torsional stresses. In most cases, safety factors in bending calculated from force/video data are lower than those determined from strain data, but are
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mechanics of Limb bone loading during terrestrial locomotion in the green iguana iguana iguana and american alligator alligator mississippiensis
The Journal of Experimental Biology, 2001Co-Authors: Richard W Blob, Andrew A BiewenerAbstract:In vivo measurements of strain in the femur and tibia of Iguana iguana (Linnaeus) and Alligator mississippiensis (Daudin) have indicated three ways in which Limb bone loading in these species differs from patterns observed in most birds and mammals: (i) the Limb Bones of I. iguana and A. mississippiensis experience substantial torsion, (ii) the Limb Bones of I. iguana and A. mississippiensis have higher safety factors than those of birds or mammals, and (iii) load magnitudes in the Limb Bones of A. mississippiensis do not decrease uniformly with the use of a more upright posture. To verify these patterns, and to evaluate the ground and muscle forces that produce them, we collected three-dimensional kinematic and ground reaction force data from subadult I. iguana and A. mississippiensis using a force platform and high-speed video. The results of these force/kinematic studies generally confirm the loading regimes inferred from in vivo strain measurements. The ground reaction force applies a torsional moment to the femur and tibia in both species; for the femur, this moment augments the moment applied by the caudofemoralis muscle, suggesting large torsional stresses. In most cases, safety factors in bending calculated from force/video data are lower than those determined from strain data, but are as high or higher than the safety factors of bird and mammal Limb Bones in bending. Finally, correlations between Limb posture and calculated stress magnitudes in the femur of I. iguana confirm patterns observed during direct bone strain recordings from A. mississippiensis: in more upright steps, tensile stresses on the anterior cortex decrease, but peak compressive stresses on the dorsal cortex increase. Equilibrium analyses indicate that bone stress increases as posture becomes more upright in saurians because the ankle and knee extensor muscles exert greater forces during upright locomotion. If this pattern of increased bone stress with the use of a more upright posture is typical of taxa using non-parasagittal kinematics, then similar increases in load magnitudes were probably experienced by lineages that underwent evolutionary shifts to a non-sprawling posture. High Limb bone safety factors and small body size in these lineages could have helped to accommodate such increases in Limb bone stress.
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Interspecific scaling of the hindLimb skeleton in lizards, crocodilians, felids and canids: does Limb bone shape correlate with Limb posture?
Journal of Zoology, 2000Co-Authors: Richard W BlobAbstract:During locomotion, lizards and crocodilians generally use a more sprawling Limb posture than most mammals and experience substantial axial rotation of the femur. Consequently, the Limb Bones of most mammals are loaded predominantly in bending, but the Limb Bones of lizards and crocodilians are loaded primarily in torsion. As body size increases, torsional shear stress in Limb Bones is expected to increase more than bending stress; therefore, Limb bone diameters of lizards and crocodilians might be expected to scale with relatively greater positive allometry than Limb bone diameters of mammals that use upright posture. To test this hypothesis, scaling patterns of the femur and tibia in lizards (iguanians and varanids) and crocodilians were compared with patterns in felid and canid mammals, using both non-phylogenetic statistical methods and phylogenetically independent contrasts. Comparisons with theoretical models indicate that size-related changes in Limb bone geometry do not completely compensate for size-related increases in Limb bone stress in the lizard or crocodilian lineages examined. Unless lizards and crocodilians compensate for size-related increases in Limb bone stress through other mechanisms (e.g. changes in Limb kinematics or the mechanical properties of Limb Bones), Limb bone stresses are predicted to be relatively greater among larger species of these lineages. However, Limb bone diameters appear to scale with greater positive allometry (relative to body mass) in varanids than in iguanians, suggesting that larger lizard lineages might compensate for increased stress through changes in bone geometry to a greater degree than smaller lineages. Allometric scaling patterns for many Limb bone diameters among iguanians are more similar to those of felids and canids than to those of varanids; thus, sprawling locomotor habits do not correlate clearly with a particular pattern of Limb bone scaling. This suggests that similarity of interspecific scaling patterns of Limb bone lengths and diameters is not sufficient to justify inferences of similar locomotor function.
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in vivo locomotor strain in the hindLimb Bones of alligator mississippiensis and iguana iguana implications for the evolution of Limb bone safety factor and non sprawling Limb posture
The Journal of Experimental Biology, 1999Co-Authors: Richard W Blob, Andrew A BiewenerAbstract:Limb postures of terrestrial tetrapods span a continuum from sprawling to fully upright; however, most experimental investigations of locomotor mechanics have focused on mammals and ground-dwelling birds that employ parasagittal Limb kinematics, leaving much of the diversity of tetrapod locomotor mechanics unexplored. This study reports measurements of in vivo locomotor strain from the Limb Bones of lizard ( Iguana iguana) and crocodilian (Alligator mississippiensis) species, animals from previously unsampled phylogenetic lineages with nonparasagittal Limb posture and kinematics. Principal strain orientations and shear strain magnitudes indicate that the Limb Bones of these species experience considerable torsion during locomotion. This contrasts with patterns commonly observed in mammals, but matches predictions from kinematic observations of axial rotation in lizard and crocodilian Limbs. Comparisons of locomotor load magnitudes with the mechanical properties of Limb Bones in Alligator and Iguana indicate that Limb bone safety factors in bending for these species range from 5.5 to 10.8, as much as twice as high as safety factors previously calculated for mammals and birds. Limb bone safety factors in shear (3.9‐5.4) for Alligator and Iguana are also moderately higher than safety factors to yield in bending for birds and mammals. Finally, correlations between Limb posture and strain magnitudes in Alligator show that at some recording locations Limb bone strains can increase during upright locomotion, in contrast to expectations based on size-correlated changes in posture among mammals that Limb bone strains should decrease with the use of an upright posture. These data suggest that, in some lineages, strain magnitudes may not have been maintained at constant levels through the evolution of a non-sprawling posture unless the postural change was accompanied by a shift to parasagittal kinematics or by an evolutionary decrease in body size.
Jason L Heaton - One of the best experts on this subject based on the ideXlab platform.
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
Journal of Human Evolution, 2019Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea JashashviliAbstract:Abstract Due to its completeness, the A.L. 288-1 (‘Lucy’) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus -like chimp/human last common ancestor (CLCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma ‘Little Foot’ (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. We found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus , as represented by StW 573 and A.L. 288-1, exhibit a significantly different ( p Ardipithecus and Australopithecus , followed by a considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens .
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the long Limb Bones of the stw 573 australopithecus skeleton from sterkfontein member 2 descriptions and proportions
bioRxiv, 2018Co-Authors: Jason L Heaton, Travis Rayne Pickering, Kristian J Carlson, Robin H Crompton, Tea Jashashvili, Amélie BeaudetAbstract:Due to its completeness, the A.L. 288-1 ("Lucy") skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its Limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like most recent common ancestor (MRCA); (2) indication of some degree of cLimbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of A. sediba (MH1 and MH2) and A. afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and Limb proportions. Yet, no early hominin is as complete (>90%), as is the ~3.67 Ma "Little Foot" (StW 573) specimen, from Sterkfontein Member 2. Here, we provide the first descriptions of that skeletons upper and lower long Limb Bones, as well as a comparative context of its Limb proportions. As to the latter, we found that StW 573 possesses absolutely longer Limb lengths than A.L. 288-1, but both skeletons show similar Limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1s Limb proportions. In fact, our multivariate allometric analysis suggests that Limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, developed along a significantly different (p < 0.001) allometric scale than that which typifies modern humans and African apes. Our analyses also suggest, as have those of others, that hominin Limb evolution occurred in two stages with: (1) a modest increase in lower Limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by (2) considerable lengthening of the lower Limb along with a decrease of both upper Limb elements occurring between Australopithecus and Homo sapiens.