Hindlimb function in the alligator: integrating movements, motor patterns, ground reaction forces and bone strain of terrestrial locomotion

Abstract

Alligator hindlimbs show high torsional loads during terrestrial locomotion, in sharp contrast to the bending or axial compressive loads that predominate in animals that use parasagittal limb movements. The present study integrates new data on hindlimb muscle function with previously obtained data on hindlimb kinematics, motor patterns, ground reaction forces and bone strain in order to (1) assess mechanisms underlying limb bone torsion during non-parasagittal locomotion in alligators and (2) improve understanding of hindlimb dynamics during terrestrial locomotion. Three dynamic stance phase periods were recognized: limb-loading, support-andpropulsion, and limb-unloading phases. Shear stresses due to torsion were maximized during the limb-loading phase, during which the ground reaction force (GRF) and caudofemoralis (CFL) muscles generated opposing moments about the femur. Hindlimb retraction during the subsequent stance-and-propulsion phase involves substantial medial rotation of the femur, powered largely by coordinated action of the GRF and CFL. Several muscles that actively shorten to flex and extend limb joints during stance phase in sprawling and erect quadrupeds act in isometric or even eccentric contraction in alligators, stabilizing the knee and ankle during the support-andpropulsion phase. Motor patterns in alligators reveal the presence of local and temporal segregation of muscle functions during locomotion with muscles that lie side by side dedicated to performing different functions and only one of 16 muscles showing clear bursts of activity during both stance and swing phases. Data from alligators add to other recent discoveries that homologous muscles across quadrupeds often do not move joints the same way as is commonly assumed. Although alligators are commonly considered models for early semi-erect tetrapod locomotion, many aspects of hindlimb kinematics, muscle activity patterns, and femoral loading patterns in alligators appear to be derived in alligators rather than reflecting an ancestral semi-erect condition.

Trackways of the American Crocodile (Crocodylus acutus) in Northwestern Costa Rica: Implications for Crocodylian Ichnology

“…The functional morphology and kinematics of crocodylian terrestrial locomotion have received considerable attention (von Huene, 1913;Schaeffer, 1941;Zug, 1974;Brinkman, 1980;Parrish, 1987;Frey, 1988;Gatesy, 1991;Reilly and Elias, 1998;Biewener, 1999, 2001;Salisbury and Frey, 2000;Renous et al, 2002;Richardson et al, 2002;Meers, 2003;Reilly and Blob, 2003;Willey et al, 2004;Reilly et al, 2005;Hutchinson, 2006;Carpenter, 2009;Allen et al, 2010;Kubo and Ozaki, 2009;Kubo, 2010b;Hutson and Hutson, 2012, 2013Baier and Gatesy, 2013;Grigg and Kirshner, 2015). Several features of our American crocodile trackways clearly are consistent with the results of kinematic analyses of high-walking.…”

Locomotor loading mechanics in the hindlimbs of tegu lizards (Tupinambis merianae): comparative and evolutionary implications

“…This orientation of torsional loading is the opposite of what would be predicted from GRF rotational moment data (see Fig.4). This suggests that the net torsional loads experienced as strains on the femur must be produced by the contraction of the CFL and other retractor muscles against the rotational moment of the GRF (Reilly et al, 2005). Femoral shear strains in tegus exceeded mean peak principal strain measurements (compressive) by only 17% (Table5; Fig.7), somewhat lower than mean values reported for the femur in alligators and iguanas (Blob and Biewener, 1999).…”

“…In tegus, peak shear stresses from the fastest individual were 1.3±0.2MPa (Table4), moderately smaller than values seen in alligators [1.9±0.5MPa (Blob and Biewener, 2001)], but considerably smaller than values from salamanders [4.1±0.3MPa (Sheffield and Blob, 2011)], iguanas [5.8±2.8MPa (Blob and Biewener, 2001)] or turtles [13.7±0.5MPa (Butcher and Blob, 2008a)]. Elevated torsion has been predicted for species that drag a large tail on the ground, because the resistance to forward motion caused by the tail could impose a larger torsional moment on the hindlimb (Reilly et al, 2005). Results from this study correspond with others (Blob and Biewener, 2001;Butcher and Blob, 2008a;Sheffield and Blob, 2011) in showing that although dragging a tail K. M. Sheffield and others may contribute to femoral shear stress, it is not the only factor that produces torsion.…”

Bases ósseas e musculares dos cortes comerciais da cauda de jacaré-do-Pantanal (Caiman yacare Daudin 1802)

“…A partir da quinta VCa, o caudofemoral longo insere-se também na superfície ventrolateral dos processos transversos dessas vértebras, estendendo-se até o desaparecimento dos mesmos. A área de inserção desse músculo em A. mississippiensis é menor, pois se estende das superfícies ventrais da segunda à oitava Vca e da superfície lateral dos primeiros 11 ou 13 dos processos hemais (Wilhite, 2003), o que é diferente do observado por Reilly et al (2005) para a mesma espécie.…”

“…Estudos sobre essa região abordam aspectos morfofisiológicos (Frey et al, 1989;Reilly et al, 2005), evolutivos (Schwarz-Wings et al, 2009; Persons e Currie, 2011) e tecnológicos, referentes ao melhor aproveitamento industrial da carne (Vicente Neto et al, 2010;Vieira et al, 2012). No entanto, caracterização óssea e muscular de cada corte comercial, que permita seu melhor aproveitamento durante a desossa, é desconhecida, assim como a própria constituição do ventre muscular.…”