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Bipedal Hominid and Quadrupedal Apes: Muscle and Skeletons

Differences between your hip skeleton and musculature of bipedal hominid and quadrupedal apes.

  1. Ilium


Reduced height, relative wideness (it's important in bipedal posture, because the weight of your body does not concentrate onto the spinal-cord only).

Orientation of blade (the curvature and the mediolateral orientation of the iliac cutting blades help the Glutei medius and minimi to act as abductors and they can also assist in support of the trunk. This curved shape also helps in controlling the chest muscles during locomotion, because the external and inner oblique muscles attach to the iliac crest).

Acetabular margin and the well-developed anterior second-rate iliac spinal column (AIIS) reflects the bipedal locomotion. Rectus femoris took its source here, that stretches the knee at the leg. Rectus femoris is very important in a few of the leaping and clinging prosimians, as the galagos and lemurs, because Rectus femoris is a leaping muscle in them. Nevertheless, in apes, there is no large AIIS. AIIS is also a place for the iliofemoral ligament in humans that prevents the hip joint from overextending.


There is not a S-shaped curve noticeable at the iliac crest and the crest tasks laterally. Therefore, the iliac fossa orients anteriorly and the gluteal surface tasks posteriorly. This orientation helps to keep the trunk in an upright position during sitting or squatting. In the event if they want to walk bipedally, the Glutei medius and minumi muscles medially rotate the flexed thigh at the hip - while in humans they abduct the expanded thigh.

The long iliac crest can be an version to climbing. Latissimus dorsi origins from here and inserts into the humerus. Because this is one of the most crucial climbing-muscles, the much longer the iliac crest is, the better aid is in climbing.

The auricular surface and the iliac tuberosity are smaller in apes. It is mainly because of the proven fact that their weight does not give attention to their pelvic region and lower limbs (hind limbs).

  1. Ischium


Ischial tuberosity is an attachment for the hamstring muscles (Biceps femoris, Semitendinosus, Semimembranosus and Adductor magnus hamstring part). At an excellent pressure during the bipedal position, the posterior part of the sacrum elevates, and pulls upwards the ischial tuberosity. The ischial tuberosity - which is located just below the fantastic sciatic notch - reflects the bipedalism.


Long ischium.

The ischial tuberosity is wider in apes than it is within humans and it generally does not look so "pulled-up" in apes. The ischial tuberosity lacks the facets for the hamstring and adductor muscles.

  1. Pubis


Pubic crest and pubic tubercle are essential in bipedal locomotion as well, because the pubic crest functions as an connection for Rectus abdominis that supports the guts and pubic tubercle is from the inguinal ligament, which assists with helping the trunk.

The iliopubic eminence is the divider of the Anterior Superior Iliac Vertebrae (ASIS) and the AIIS. Here takes place the iliopsoas muscle that helps in flexing the hip and promoting the chest muscles on the hip joint.


Apes lack each one of these individuals characteristics at the pubis: they don't have a pubic crest nor tubercle, and because their pelvis orient in different ways, their ilipsoas groove and iliopubic eminence are missing.

The pubic symphysis in apes are usually fuses alongside one another, while it only rarely happens in humans.

  1. Acetabulum


The orientation of the acetabulum is inferior-lateral-anterior. The superior margin of acetabulum must handle the largest weight/pressure, it developed a very heavy cartilage, so do the top of the femur. This is called laubrum. Very strong, Z-shaped, ligaments are present here. The depth of the acetabulum can reveal a lot about the freedom of the hip joint. When the acetabulum is shallow, it reflects more flexibility. The acetabulum in humans is shallow compared to many of the African apes (but chimpanzees), but it is deep compared to the orang-utans.


The ligaments are weaker than in humans.

  1. Sacrum, coccyx


The individuals sacrum consists of five fused vertebrae averagely. However, it could be varied between four and six. The coccyx stands from four fused vertebrae, usually.

The sacrum in humans is wider than in apes and it is not long as an ape sacrum. This original condition is very distinctive regarding to bipedalism. The wider sacrum means more distance between your sacroiliac joint, which assists with moving the weight and the pressure from pubic symphysis. A wider distance as of this joint also means a more substantial birth-canal.


In apes and monkeys the amount of the fused vertebrae of the sacrum and coccyx may vary from types to species.

The form of the sacrum is not so wide plus more elongated. It discloses that they do not support so huge weight on the pelvic region as do the humans.

  1. Femur


The real human femur is longer than that of an ape.

The lateral condyle in humans is more visible.

The bicondylar surface is greater in humans than in apes. It is due to centre of gravity of the body.


Medial condyle is much larger in apes.

More overall flexibility at the hip joint.

B, Actions of muscles at the leg and ankle joint parts during bipedal locomotion. Observed features in ancestral hominid fossils.

Extensors of the leg at the leg joint:

    • Tensor fasciae latae
    • Quadriceps femoris muscles (Rectus femoris, Vasti lateralis, medialis, intermedius)

    Flexors of the knee at the knee joint:

      • Sartorius
      • Gracilis (also can assist in medial rotation)
      • Hamstring muscles (Biceps femoris it is also the lateral rotator of the knee joint, Semimembranosus, Semitendenosus they also medially rotate the knee joint when the leg is flexed
      • Gastrocnemius
      • Popliteus (weakened flexor, but it is just a medial rotator of the lower leg)
      • Plantaris

      Muscles that act at the ankle joint (talotibial) joint:

        • Tibialis anterior (dorsiflexion)
        • Extensor hallucis longus (dorsiflexion)
        • Extensor digitorum longus (dorsiflexion)
        • Peroneus tertius (dorsiflexion)
        • Peroneus longus and brevis (plantar flexion)
        • Gastrocnemius (plantar flexion)
        • Soleus (plantar flexion)
        • Plantaris (plantar flexion)
        • Flexor digitorum longus (plantar flexor)
        • Tibialis posterior (plantar flexor)

        Fossil files:

        Australopithecus afarensis:

        The tibia and the fibula are very interesting. We are able to view adaptations to both arboreal and bipedal indicators. This is called mosaic morphology.

        The analyzed specimens: AL 129-1b, AL 288-1aq and AL 333x-26). Ape-like elements: brief border to the lateral condyle, in the first two specimens, there are features that general in the apes (under the epicedial there was the "hollowed-out appearance") which means that the Tibialis posterior attached to the lateral aspect of the tibia rather than the posterior area. Other parts - such as semimembranosus and gracilis are also somewhat ape-like.

        Nevertheless, other A. afarensis specimens show bipedal characteristics:

        Distal articulation surface of the tibia (the angle of the rearfoot and the tibia and fibula). But, just as before, there are ape-like features also on the distal part of fibula: the path of the articular facet, (orients distally rather than medially just as the modern humans), they may have an anteriorly oriented peroneal groove on their fibulae while it faces laterally in modern humans. The A. afarensis Lucy (AL 288-1) also possesses these mosaic morphological features: the posteriorly oriented distal tibial angle shows similarities with the apes, while in other afarensis specimens the position is lateral, which really is a human being feature. The holding perspective at the leg joint also shows more similarities to the modern human specimens. This may reveal an individual arboreal behavior of Lucy, and a more developed bipedalism in the other specimens.

        Homo habilis:

        The H. habilis specimens do not cause so many quarrels than the australopithecines. They have more human like features in their lower legs and less ape-like features. Although, they don't lack these features (rounded anterior border of the tibia, in humans the insertion area of the Flexor digitorum longus is bigger than that of the tibialis posterior - it is quite contrary in the habilis. The accessories of other muscles - soleus, popliteus - show sort of a changeover between apes and humans, etc. ).

        The Neanderthals:

        The fibula and the tibia are very robust, but carry the individual characteristics.

        Q2, Evolution of the first hominid foot

        The main characteristics of the individuals foot include the presence of the arches, the calcaneocuboid joint, the proportions of the major elements of the foot, the condition of the ankle-joint and the actual fact that the hallux cannot be opposed.

        The arches in feet are very unique, the apes don't have arches (they have got only 1 arch, the transverse arch). In humans, in addition to the plantar aponeurosis, there are other ligaments that aid in having these arches: the planting season ligament, the short plantar ligament and the long plantar ligament. The distance of the distal digits of the toes are much shorter in humans than in apes, however, the size of the best toe is approximately the same.

        The foot of Australopithecus afarensis, such as in the leg, shows mosaic morphology. This means that one features are similar to the modern humans, while some discuss similarities with the apes.

        The human-like morphology: the talus - which also has both individuals and ape characteristics - alongside the tibia and fibula, shows a far more real human like joint at the talotibia. Although, the condition of the talus is rather ape-like. Other indications that reveal a more human being appearance in the afarensis foot are the talar trochlear shape, the direction of the ankle joint's axis and of the Flexor hallucis longus's groove which suggest that the movements of the afarensis were very similar to those of the modern humans.

        The shape of the fifth metatarsals disclose a very similar ability of dorsiflexion as it is present in modern humans. Their navicular bones in appearance will be more ape-like, however the existence of the groove of the spring ligament proves that they could have similar arches than the modern humans have. The opportunity of the bipedal locomotion can be traced down also by the human-like lateral cuneiform, although, its hook helps it be look more ape like.

        Nevertheless, the ape-like curves of the phalanges suggest that they might be arboreal. The calcareous likewise have both human and ape like features, the medial cuneiform is rather ape like, so is the first metatarsal's rounded head.

        The ft. of Paranthropus robostus has several human-like characteristics. These features are the pursuing: the hallux probably was adducted unlike in the apes where in fact the big toe is rather abducted, the plantar ligaments suggest similarities to the real human feet, the first metatarsal shows that it bore more weight than the apes due to its robust appearance, but other features on the first metatarsal bone reveal ape-like features, too. According to the article of Susman and Brain (1988, brought up in Aiello and Dean), it's very likely that the Paranthropus robostus was bipedal however in a different way than the present day humans.

        The foot of the Homo habilis:

        The biggest discussion is triggered by the tarsal bones of a young Homo habilis (OH 8 from Olduvai Gorge), because some research workers do not feel that the individuals characteristics of the specimen's ft. bones are sufficient to be classified as humans. The elements of the foot show the signs of the bipedalism - even those trust this who do not think that this specimen has a right to be included in to the Homo genus - but, perhaps, in a totally different way as it is seen in the modern humans. Another talus bone, the KNM-ER 813 from Koobi Fora, has less problems with its classifications, as it shows more similarities to the talus of the modern humans. The first metatarsal is the most strong, and the fifth metatarsal bone of the OH 8 is the second, while in apes the fifth metatarsal bone is the weakest. The size of the foot amount of the OH 8 is also more similar to the structure of the human foot.

        The fossil record shows that the opposability of the big toe of OH 8 is not present, but the adduction of it can be observed. The power of grasping is also more than likely, though.

        The base of the Neanderthals:

        Interestingly, the evidences show you that the opposability of the big feet might be somewhere between the present day humans and the living apes. Others deny it, because of the more human characteristics in the tarsometatarsal joint, which may be varied on a great size even in modern humans. Typical Neanderthal features will be the short proximal phalanx of the big bottom and the short neck of the talus.

        The possible symptoms of the bipedalism in the fossil evidences:

        Apart from the bones of the foot other skeletal remains can reveal the erected body posture and the possible bipedal walking habits. A relative much longer arm may be a signal of the arboreal life-style, or partly arboreal living circumstances. Nevertheless, Lucy has relatively brief fingertips, not ape-like, long ones (JOHANSON-EDEY 1990) The shape of scapula and the orientation of the glenoid fossa also can help answer this question. A small fragment of your Australopithecus afarensis scapula suggests that its owner had a far more ape-like in this question, than human being like. In apes the glenoid fossa faces to the cranium which feature can be viewed also in case there is this fragment. A far more complete scapula - which derives from an A. africanus (Sts 7) - can tell us additional information about the possible functions of the pectoral girdle. This scapula looks very similar to the scapula fragment of the afarensis specimen (AL 288-1l), and they both carry more similarities to the pectoral girdle of the apes, especially to the orang-utans. The ribcage has more ape-like characteristics in its appearance. The form of the vertebral column, however, widens distally (the lumbar vertebrae will be the widest) as it seems in humans, which is another possible signal of the bipedal locomotion. The pelvic girdle shows more evidences for the mosaic morphology just as before. The iliac crest is quite human-like, though it is more elongated laterally and the acetabulum orients more anteriorly. Perhaps this is why why A. afarensis has a relatively very long femoral neck of the guitar. The iliac blades immediate interiorly, as well. The shape of the sacrum is very extensive - another human-like sign, however its posterior section is not as curved anteriorly as it is in the modern humans.

        According to Johanson (JOHANSON-EDEY 1990), Lucy's pelvis is designed to the bipedal locomotion as well as to the possibility to give life to large-headed infants, as her pelvis is so extensive.

        All these features make likely that the A. afarensis could walk bipedally, however in a more complicated way. The anteriorly confronted acetabulum could end result a very heavy bipedalism. In the femoral head, we can see a more powerful fovea than it is on the femoral head of the present day human.

        In quadrupeds the tibial tuberosity is more rounded and less pointed. The "sharpness" of the tibial tuberosity is a more human being (or bipedal) characteristic. This sharpness can be viewed in Lucy, although her tibia appears more robust compared to the very high juvenile, the Turkana guy (H. erectus).

        In proximal femur of the Australopithecines, there are a comparable amount of similarities to humans (the assorted presence of the intertrochanteric collection and the Obturator externus groove) than to chimpanzees (the small femoral head and the non-flaring better trochanter) and the unique features (long femoral neck of the guitar, compressed femoral neck-cross section), the more similarities to humans in the question of the distal femur (the high/very high bicondylar perspective, the elliptical shaped lateral epicedial profile), and its own unique phenomena in the epiphysis shape and symmetry, but the femoral shaft's more similarity to the chimpanzees offers us an extremely eclectic impression about the possible locomotion of the Australopithecines.

        As I had written in the 1B question, the base of the Australopithecines show very varied picture as well. It reveals both individuals and ape like features - such as almost anything else in the Australopithecus skeleton. A lot more human like elements of the foot are the human-like rearfoot, the power of a better dorsiflexion, the expanded foot of the fifth metatarsal, the wide calcaneus and the presence of the longitudinal arch.

        On the other side, there are several ape-like characteristics, like the shape of the phalanges, the tuberosity of the calcaneous comes with an oval orientation, also offers an enormous peroneal tubercle, the already mentioned ape-like shape of the "hook" of the lateral cuneiform bone, and the rounded brain of the first metatarsal.

        Summarising, the mosaic morphology in the Australopithecines are extremely firmly present, they reveal similarities to the humans, as well regarding the apes, but they also developed own features. It's very likely that they were modified to the bipedal locomotion, but not in a modern human being way.

        The essay has been compiled by using the following literature as a guide-line:

        Aiello and Dean, 2006: An Advantages To People Evolutionary Anatomy, reprinted in 2006, Elsevier Academics Press, London

        The materials through the Demo-sessions


        JOHANSON-EDEY, 1990: Lucy - The Beginnings of Humankind, Penguin Books, London, 1990.

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