Pelvic and thigh musculature in frogs (Anura) and origin of anuran jumping locomotion

Abstract

Comparative analysis of the anuran pelvic and thigh musculoskeletal system revealed that the thigh extensors, responsible for the initial phase of jump, the propulsive stroke in swimming and, if used asynchronously, also for walking, are least affected by the transformations observed between anurans and their temnospondyl ancestors (as reflected in contemporary caudates). The iliac shaft and urostyle, two of the most important anuran apomorphies, represent skeletal support for muscles that are mostly protractors of the femur or are important in attaining a crouching position, a necessary prerequisite for rapid escape. All of these muscles originate or insert on the iliac shaft. As the orientation of the pubis, ischium and ilium is the same in anurans, caudates and by inference also in their temnospondyl ancestors, it is probable that the pelvis was shifted from the sacral vertebra posteriorly along the reduced and stiffened tail (urostyle) by the elongation of the illiac shaft. Thus, the original vertical orientation of the ilium was maintained (which is also demonstrated by stable origins of the glutaeus maximus, iliofemoralis and iliofibularis on the tuber superius) and the shaft itself is a new structure. A review of functional analysis of anuran locomotion suggests some clear differences from that in caudates, suggesting that terrestrial jumping may have been a primary locomotor activity, from which other types of anuran locomotion are derived.

Inverse dynamic modelling of jumping in the red-legged running frogKassina maculata

“…Many of the major muscles that power jumping originate on the lateral aspect of the ilium and insert at or distal to the knee (Prikyl et al, 2009); thus, variations in starting posture at different jump angles would change the moment arms and, potentially, the action of these muscles. Indeed, demonstrated that frog hind limb muscles have different functions depending on task and limb configuration.…”

Passive stiffness of hindlimb muscles in anurans with distinct locomotor specializations

“…The tissues directly connected to the cruralis (fascia lata, tensor fasciae latae and gluteus maximus) were cut in cross-section but left in place. The cruralis originates on the ilium just ventral to the acetabulum and inserts via a broad aponeurosis that covers the knee onto the tibiofibular (Prikryl et al, 2009), so to account for the small moment arm around the hip, the moment arm of the cruralis muscle at the knee was determined with the hip joint kept constant at 90 • . Moment arms were measured for 6 cruralis and 4 plantaris muscles for Kassina, 5 cruralis and 7 plantaris for Lithobates, 4 cruralis and 7 plantaris for Rhinella and 3 cruralis and 8 plantaris for Xenopus.…”

Do all frogs swim alike? The effect of ecological specialization on swimming kinematics in frogs

“…Frogs are characterized by a shortened trunk and tail, elongated ilia and elongated hind limbs. This morphology has been interpreted as being associated with a jumping life style and thus it has been suggested that jumping evolved early in the evolution of the lineage (Gans and Parsons, 1966;Shubin and Jenkins, 1995; Jenkins and Shubin, 1998) and many recent studies have attempted to infer locomotion in basal frogs (Prikryl et al, 2009; Essner et al, 2010;Reilly and Jorgensen, 2011;Sigurdsen et al, 2012;Venczel and Szentesi, 2012; Jorgensen and Reilly, 2013). However, kinematic and electromyographic studies indicate strong similarities between the mechanics of swimming and jumping in some frogs (Emerson and De Jongh, 1980;Peters et al, 1996; but see Nauwelaerts and Aerts, 2003), implying that morphological features associated with these two locomotor modes may not be that different.…”