In fish, hypaxial musculature allows for movement of the pelvic fin as it does the pectoral fin.

SHARK

LUNGFISH

TENSOR FASCIA LATA

Early tetrapods possess an iliofemoralis muscle which separated to form the tensor fascia latae, pyriformis, and gluteus muscles of mammals (Kardong, p. 387).  The gluteus maximus isn’t well separated from tensor fascia latae and caudofemoralis in many animals (Hartman, 1933, p. 151).

CHICKEN

CAT

GOAT

COW

MONKEY

GLUTEAL MUSCLES

The gluteal muscles abduct the hip.  In humans, the gluteus maximus has been modified to become a hip extensor.

FROG

ALLIGATOR

OPOSSUM

CAT

CAT

GOAT

SHEEP

COW

PIG

MONKEY

     The primitive condition of the gluteus maximus (gluteus superficialis) which is retained in prosimians and many New World monkeys is that of a flat, triangular muscle.  Its fascia sheet originates from the transverse processes of caudal vertebrae, it passes over the hip joint, and it inserts on the femur, distal to the greater trochanter (Stern, 1972).  There are some variations known in the muscle such as variable separation from the tensor fascia latae in prosimians, substantial innervation by the superior gluteal nerve in the genus Lemur, and the distal limit of the insertion (which is can reach the lateral condyle of the femur, or perhaps even the knee capsule in cheirogalienes, proximal to the lateral condyle in lemurines, and the upper two thirds of the femur in indriids and tarsiers).  In New World monkeys, the number of caudal vertebrae involved in the origin can vary and as can the insertion, which does not extend as distally as in prosimians.  While the gluteus medius is larger than the gluteus superficialis in most New World monkeys, they are similar in size in the genus Cebus and the gluteus superficialis is the larger of the two in Saimiri (Stern, 1972).

     In Old World monkeys, the origin is usually limited to the first two caudal vertebrae (although the third may be involved and the origin may be limited to the first caudal vertebra only).  The gluteus superficialis is less than half the size of the gluteus medius and the insertion is usually limited to the upper half of the femur (Stern, 1972).

     In gibbons, the gluteus superficialis originates from the sacrum and the first coccygeal vertebrae and the insertion can extend to the femoral midpoint.  In African apes, the distal insertion of the superficialis can extend two thirds down the length of the femur, and often farther.  In chimps, the medius is larger than the superficialis but in gorillas the two are similar in size.  In orangutans, the posterior portion of the superficialis is reduced as is the distal extension of its insertion (Stern, 1972).

     In humans, the gluteus maximus is unique in its strong origin from the ilium in addition to origins on the sacrum and coccyx (although a tendon does reach the ilium in siamangs).  Humans are also unique in the enlarged origin from the fascia over the multifidus muscle.  The majority of the muscle does not extend farther distally than one fourth the length of the femur.  The cranial portion of the gluteus maximus is much larger contributing to for the increased size of the muscle in humans (and perhaps entirely responsible for the size increase), which is more than twice the size of the gluteus medius.  This condition is unique in primates (Stern, 1972).

     The gluteus maximus is not active in a standing stance and some individuals do not use it when walking.  It has no specific role in walking and walking may be unimpaired by its paralysis.  The muscle may play a more important role in jogging and running and it may be this locomotion style which drove the modification of the muscle in human ancestors.  The gluteus maximus is an extensor of the thigh in both humans and chimps, but its modifications in humans increase its efficiency, especially in running.  The gluteus maximus muscle, and its cranial portion specifically, are important in forceful abduction and in maintaining stability when the body is supported on one leg (Stern, 1972).

     There is no single major feature which enabled bipedality in hominids but rather a combination of smaller changes (Robinson, 1972).  Perhaps the first of the changes which allowed bipedality was a shift in the center of gravity from the midtrunk (as in chimps) to the pelvic cavity (as in humans).  In chimps the gluteus medius functions as an extensor unlike the gluteus medius in humans.  The shortening of the ischium was important in modifying the line of function of hamstring muscles (Robinson, 1972).  The muscles of Australopithecus afarensis were not as efficient at supporting bipedal locomotion as those of modern humans (Wang, 2004c).

     The gluteus medius in chimps (the largest gluteal muscle) is primarily an extensor rather than an abductor, as it is in humans.  As a result, chimps lack lateral balance control.  In humans, the change in the position of the iliac blades allowed the gluteus medius (and minimis) to provide effective lateral balance which is lacking in chimps.  While both Paranthropus and Australopithecus were bipedal, Australopithecus had a short ischium, more elongated leg and a more human like foot, suggesting it was more adapted for running (Robinson, 1972)

HUMAN