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Alligator hindlimb muscles involved in the high walking for which electromyographical data have been recorded. Lines of actions are indicated for muscles active in either stance phase (red), swing phase (blue) or with activity in both phases (black); gray shading in arrows indicates that the muscle lies medial to the femur. AMB1, ambiens, head 1; ADD1, adductor femoris 1; CFL, caudofemoralis longus; FMTI, femorotibialis internus; FTE, flexor tibialis externus; FTI2, flexor tibialis internus, head 2; G, gastrocnemius; ILFEM, iliofemoralis; ILFIB, iliofibularis; ILTIB1/2 iliotibialis, head 1/2; PIFE2/3, puboischiofemoralis externus, head 2/3; PIFI2, puboischiofemoralis internus, head 2; PIT, puboischiotibialis; TA, tibialis anterior. Data for muscles marked with asterisks are taken from Gatesy (1997). The continuation of the AMB1 tendon through the extensor sheet and into the Achilles tendon is not shown. 

Alligator hindlimb muscles involved in the high walking for which electromyographical data have been recorded. Lines of actions are indicated for muscles active in either stance phase (red), swing phase (blue) or with activity in both phases (black); gray shading in arrows indicates that the muscle lies medial to the femur. AMB1, ambiens, head 1; ADD1, adductor femoris 1; CFL, caudofemoralis longus; FMTI, femorotibialis internus; FTE, flexor tibialis externus; FTI2, flexor tibialis internus, head 2; G, gastrocnemius; ILFEM, iliofemoralis; ILFIB, iliofibularis; ILTIB1/2 iliotibialis, head 1/2; PIFE2/3, puboischiofemoralis externus, head 2/3; PIFI2, puboischiofemoralis internus, head 2; PIT, puboischiotibialis; TA, tibialis anterior. Data for muscles marked with asterisks are taken from Gatesy (1997). The continuation of the AMB1 tendon through the extensor sheet and into the Achilles tendon is not shown. 

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... The weight of the hindlimb muscles of quadrupedal tetrapod species accounts for a large proportion of body weight. Compared with the hindlimbs of other vertebrate groups, the hindlimbs of alligators have stronger compliant muscles, which enhances their mobility [23][24][25]. Alligators are unusual among tetrapods in their ability to use a wide range of hindlimb postures, even over a restricted range of speeds [26,27]. Research conducted on the skeletal muscles of hibernating animals demonstrates that their skeletal muscles exhibit well-maintained strength and anti-fatigue capabilities throughout the period of hibernation [28][29][30]. ...
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We developed a three‐dimensional, computational biomechanical model of a juvenile Nile crocodile (Crocodylus niloticus) pelvis and hindlimb, composed of 47 pelvic limb muscles, to investigate muscle function. We tested whether crocodiles, which are known to use a variety of limb postures during movement, use limb orientations (joint angles) that optimise the moment arms (leverages) or moment‐generating capacities of their muscles during different limb postures ranging from a high walk to a sprawling motion. We also describe the three‐dimensional (3D) kinematics of the crocodylian hindlimb during terrestrial locomotion across an instrumented walkway and a treadmill captured via X‐ray Reconstruction of Moving Morphology (biplanar fluoroscopy; ‘XROMM’). We reconstructed the 3D positions and orientations of each of the hindlimb bones and used dissection data for muscle lines of action to reconstruct a focal, subject‐specific 3D musculoskeletal model. Motion data for different styles of walking (a high, crouched, bended and two types of sprawling motion) were fed into the 3D model to identify whether any joints adopted near‐optimal poses for leverage across each of the behaviours. We found that (1) the hip adductors and knee extensors had their largest leverages during sprawling postures and (2) more erect postures typically involved greater peak moment arms about the hip (flexion‐extension), knee (flexion) and metatarsophalangeal (flexion) joints. The results did not fully support the hypothesis that optimal poses are present during different locomotory behaviours because the peak capacities were not always reached around mid‐stance phase. Furthermore, we obtained few clear trends for isometric moment‐generating capacities. Therefore, perhaps peak muscular leverage in Nile crocodiles is instead reached either in early/late stance or possibly during swing phase or other locomotory behaviours that were not studied here, such as non‐terrestrial movement. Alternatively, our findings could reflect a trade‐off between having to execute different postures, meaning that hindlimb muscle leverage is not optimised for any singular posture or behaviour. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in extant crocodiles which can form a basis for investigating muscle function in extinct archosaurs.
... We hypothesise that the space between the most posterior trunk ribs and the pelvis was occupied by an unusually large puboischiofemoralis internus 2 (PIFI2). In modern alligators, PIFI2 originates on the centra of the lumbar vertebrae (most posterior presacrals) as well as on the ventral surfaces of their transverse processes, and inserts on the anterodorsal aspect of the proximal femur (Reilly et al. 2005). In Eldeceeon, the origin of the PIFI2 fibres may have extended further forward along the posterior half of the vertebral column than in a modern alligator, such that a considerably greater number of presacrals may have provided sites for muscle attachment. ...
Article
The late Viséan anthracosauroid Eldeceeon rolfei from the East Kirkton Limestone of Scotland is re-described. Information from two originally described and two newly identified specimens broadens our knowledge of this tetrapod. A detailed account of individual skull bones and a revision of key axial and appendicular features are provided, alongside the first complete reconstructions of the skull and lower jaw and a revised reconstruction of the postcranial skeleton. In comparison to Silvanerpeton , the only other anthracosauroid from East Kirkton, Eldeceeon is characterised by a proportionally wider semi-elliptical skull, comparatively smaller nostrils set farther apart, smaller and more rounded orbits, a shorter skull table with gently convex lateral margins, and a deeper suspensorium with a straight posterior margin and a small dorsal embayment. The remarkably large hind feet and elongate toes of Eldeceeon presumably represent an adaptation for attaining high locomotory speed through increased stride length and reduced stride frequency. This would necessitate great muscle force but few muscle contractions. At the beginning of a new stride cycle, repositioning the pes anteriorly and lifting the toes off the ground would require a strong and large muscle to pull the femur upward and rotate it inward and forward. It is hypothesised that such muscle might correspond to the puboischiofemoralis internus 2 , which would extend along the posterior half of the vertebral column, consistent with the occurrence of long, curved ribs in the anterior half of the trunk. Using maximum parsimony and Bayesian inference, cladistic analyses of all major groups of stem amniotes retrieve a sister group relationship between Eldeceeon and Silvanerpeton , either as the most plesiomorphic stem amniote clade or as a clade immediately crownward of anthracosauroids.