The evolutionary anatomy Essay

A, Differences between the hip skeleton and muscular structure of two-footed hominid and four-footed apes.

  1. Troy
  2. Worlds:

    Reduced tallness, comparative broadness ( it is of import in two-footed position, because the weight of the organic structure does non concentrate onto the spinal cord merely ) .

    Orientation of blade ( the curvature and the mediolateral orientation of the iliac blades help the Glutei medius and minimi to move as kidnappers and they can besides help in support of the bole. This curving form besides helps in equilibrating the upper organic structure during motive power, because the external and internal oblique musculuss attach to the iliac crest ) .

    Acetabular border and the well-developed anterior inferior iliac spinal column ( AIIS ) reflects the two-footed motive power. Rectus femoris takes its beginning here, that extends the leg at the articulatio genus. Rectus femur is really of import in some of the spring and clinging prosimians, as the bushbaby and lemurs, because Rectus femur is a leaping musculus in them. However, in apes, there is no big AIIS. AIIS is besides a topographic point for the iliofemoral ligament in worlds that prevents the hip articulation from overstraining.

    Apes:

    There is no S-shaped curve visible at the iliac crest and the crest undertakings laterally. Therefore, the iliac pit Easts anteriorly and the gluteal surface undertakings posteriorly. This orientation keeps the bole in an unsloped place during sitting or crouching. In instance if they want to walk bipedally, the Glutei medius and minumi musculuss medially rotate the flexed thigh at the hip – while in worlds they abduct the drawn-out thigh.

    The long iliac crest is an version to mounting. Latissimus dorsi beginnings from here and inserts into the humerus. Because this is one of the most of import climbing-muscles, the longer the iliac crest is, the better assistance is in mounting.

    The otic surface and the iliac tubercle are smaller in apes. It is chiefly because of the fact that their weight does non concentrate on their pelvic part and lower limbs ( hind limbs ) .

  3. Ischium
  4. Worlds:

    Ischial tubercle is an fond regard for the hamstring musculuss ( Biceps femoris, Semitendinosus, Semimembranosus and Adductor magnus hamstring portion ) . At a superior force per unit area during the two-footed position, the posterior portion of the sacrum elevates, and pulls upwards the ischial tubercle. The ischial tubercle – which is located merely below the great sciatic notch – reflects the bipedalism.

    Apes:

    Long ischial bone.

    The ischial tubercle is wider in apes than it is in worlds and it does non look so “ pulled-up ” in apes. The ischial tubercle lacks the aspects for the hamstring and adductor musculuss.

  5. Pubis
  6. Worlds:

    Pubic crest and pubic tubercle are of import in two-footed motive power every bit good, because the pubic crest serves as an fond regard for Rectus abdominis that supports the backbones and pubic tubercle is associated with the inguinal ligament, which helps in back uping the bole.

    The iliopubic distinction is the splitter of the Anterior Superior Iliac Spine ( ASIS ) and the AIIS. Here takes topographic point the iliopsoas musculus that helps in flexing the hip and back uping the upper organic structure on the hip articulation.

    Apes:

    Apes lack all these human features at the pubic bone: they do non hold a pubic crest nor tubercle, and because their pelvis East otherwise, their ilipsoas channel and iliopubic distinction are losing.

    The pubic symphysis in apes are normally fuses together, while it merely seldom happens in worlds.

  7. Acetabulum
  8. Worlds:

    The orientation of the cotyloid cavity is inferior-lateral-anterior. The superior border of cotyloid cavity must get by with the biggest weight/pressure, it developed a really thick gristle, so did the caput of the thighbone. This is called laubrum. Very strong, Z-shaped, ligaments are present here. The deepness of the cotyloid cavity can state us a batch about the mobility of the hip articulation. If the cotyloid cavity is shallow, it reflects more flexibleness. The cotyloid cavity in worlds is shallow compared to many of the African apes ( but Pan troglodytess ) , but it is deep compared to the orang-utans.

    Apes:

    The ligaments are weaker than in worlds.

  9. Sacrum, tail bone
  10. Worlds:

    The human sacrum contains five amalgamate vertebrae averagely. However, it can be varied between four and six. The tail bone stands from four amalgamate vertebrae, normally.

    The sacrum in worlds is wider than in apes and it is non so long as an ape sacrum. This alone form is really typical sing to bipedalism. The wider sacrum means more distance between the sacroiliac articulation, which helps in reassigning the weight and the force per unit area from pubic symphysis. A wider distance at this articulation besides means a larger birth-canal.

    Apes:

    In apes and tamper the figure of the amalgamate vertebrae of the sacrum and tail bone may change from species to species.

    The form of the sacrum is non so broad and more extended. It reveals that they do non back up so immense weight on their pelvic part as do the worlds.

  11. Femur
  12. Worlds:

    The human thighbone is longer than that of an ape.

    The sidelong condyle in worlds is more outstanding.

    The bicondylar surface is larger in worlds than in apes. It is because of the Centre of gravitation of the organic structure.

    Apes:

    Medial condyle is larger in apes.

    More flexibleness at the hip articulation.

    B, Actions of musculuss at the articulatio genus and ankle articulations during two-footed motive power. Observed characteristics in hereditary hominid dodos.

    Extensor muscles of the leg at the articulatio genus articulation:

  • Tensor facia latae
  • Quadricepss femoris musculuss ( Rectus femoris, Vasti lateralis, medialis, intermedius )
  • Flexor muscles of the leg at the articulatio genus articulation:

  • Sartorius
  • Gracilis ( besides can help in median rotary motion )
  • Hamstringing musculuss ( Biceps femoris { it is besides the sidelong rotator of the articulatio genus articulation } , Semimembranosus, Semitendenosus { they besides medially revolve the articulatio genus articulation when the leg is flexed }
  • Gastrocnemius
  • Popliteus ( weak flexor, but it is a median rotator of the leg )
  • Plantaris
  • Muscles that act at the mortise joint ( talotibial ) articulation:

  • Tibialis front tooth ( dorsiflexion )
  • Extensor hallucis longus ( dorsiflexion )
  • Extensor digitorum longus ( dorsiflexion )
  • Peroneus tertius ( dorsiflexion )
  • Peroneus longus and brevis ( plantar flexure )
  • Gastrocnemius ( plantar flexure )
  • Soleus ( plantar flexure )
  • Plantaris ( plantar flexure )
  • Flexor digitorum longus ( plantar flexor )
  • Tibialis buttocks ( plantar flexor )

Dodo records:

Australopithecus afarensis:

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The shinbone and the calf bone are rather interesting. We can detect versions to both arboreal and two-footed marks. This is called Mosaic morphology.

The examined specimens: AL 129-1b, AL 288-1aq and AL 333x-26 ) . Ape-like elements: short boundary line to the sidelong condyle, in the first two specimens, there are characteristics that general in the apes ( under the epicedial there was the “ hollowed-out visual aspect ” ) which means that the Tibialis buttocks attached to the sidelong side of the tibia alternatively of the posterior side. Other fond regards – such as semimembranosus and gracilis are besides instead ape-like.

However, other A. afarensis specimens show two-footed features:

Distal articulation surface of the shinbone ( the angle of the mortise joint articulation and the shinbone and calf bone ) . But, yet once more, there are ape-like characteristics besides on the distal portion of calf bone: the way of the articular aspect, ( Easts distally instead than medially as in the modern worlds ) , they have an anteriorly oriented peroneal channel on their calf bone while it faces laterally in modern worlds. The A. afarensis Lucy ( AL 288-1 ) besides owns these Mosaic morphological characteristics: the posteriorly oriented distal tibial angle shows similarities with the apes, while in other afarensis specimens the angle is sidelong, which is a human characteristic. The transporting angle at the articulatio genus articulation besides shows more similarities to the modern human specimens. This can uncover an single arboreal wont of Lucy, and a more developed bipedalism in the other specimens.

Homosexual habilis:

The H. habilis specimens do non do so many statements than the australopithecines. They have more human like characteristics in their lower legs and less ape-like characteristics. Although, they do non miss these characteristics ( rounded anterior boundary line of the shinbone, in worlds the interpolation country of the Flexor digitorum longus is bigger than that of the tibialis posterior – it is rather the antonym in the habilis. The fond regards of other musculuss – soleus, popliteus – show kind of a passage between apes and worlds, etc. ) .

The Neandertal mans:

The calf bone and the shinbone are really robust, but bear the human features.

Q2, Evolution of the early hominid pes

The chief features of the human pes include the presence of the arches, the calcaneocuboid articulation, the proportions of the major parts of the pes, the form of the ankle-joint and the fact that the big toe can non be opposed.

The arches in pes are rather alone, the apes do non hold arches ( they have merely one arch, the transverse arch ) . In worlds, apart from the plantar aponeurosis, there are other ligaments that aid in holding these arches: the spring ligament, the short plantar ligament and the long plantar ligament. The length of the distal figures of the toes are much shorter in worlds than in apes, nevertheless, the size of the large toe is about the same.

The pes of Australopithecus afarensis, such as in the leg, shows Mosaic morphology. It means that certain characteristics are similar to the modern worlds, while others portion similarities with the apes.

The human-like morphology: the scree – which besides has both human and ape features – together with the shinbone and calf bone, shows a more human like articulation at the talotibia. Although, the form of the scree is instead ape-like. Other marks that reveal a more human visual aspect in the afarensis pes are the talar trochlear form, the way of the ankle articulation ‘s axis and of the Flexor hallucis longus ‘s channel which suggest that the motions of the afarensis were really similar to those of the modern worlds.

The form of the 5th metatarsals reveal a really similar ability of dorsiflexion as it is present in modern worlds. Their scaphoid castanetss in visual aspect are more ape-like, but the presence of the channel of the spring ligament proves that they might hold similar arches than the modern worlds have. The possibility of the two-footed motive power can be traced down besides by the human-like sidelong cuneiform, although, its hook makes it look more ape like.

However, the ape-like curves of the phalanges suggest that they might be arborical. The chalky besides have both human and ape like characteristics, the median cuneiform is instead ape like, so is the first metatarsal ‘s rounded caput.

The pes of Paranthropus robostus has several human-like features. These characteristics are the undermentioned: the big toe likely was adducted unlike in the apes where the large toe is instead abducted, the plantar ligaments suggest similarities to the human pes, the first metatarsal suggests that it bore more weight than the apes because of its robust visual aspect, but other characteristics on the first metatarsal bone reveal ape-like characteristics, excessively. Harmonizing to the article of Susman and Brain ( 1988, mentioned in Aiello and Dean ) , it is really likely that the Paranthropus robostus was two-footed but in a different manner than the modern worlds.

The pes of the Homo habilis:

The biggest statement is caused by the tarsal castanetss of a immature Homo habilis ( OH 8 from Olduvai Gorge ) , because some research workers do non believe that the human features of this specimen ‘s pes castanetss are good plenty to be classified as worlds. The elements of the pes show the marks of the bipedalism – even those agree with this who do non believe that this specimen deserves to be included into the Homo genus – but, possibly, in a wholly different manner as it is seen in the modern worlds. Another scree bone, the KNM-ER 813 from Koobi Fora, has less jobs with its categorizations, as it shows more similarities to the scree of the modern worlds. The first metatarsal is the most robust, and the 5th metatarsal bone of the OH 8 is the 2nd, while in apes the 5th metatarsal bone is the weakest. The size of the pes length of the OH 8 is besides more similar to the construction of the human pes.

The dodo record suggests that the opposability of the large toe of OH 8 is non present, but the adduction of it can be observed. The ability of grasping is besides really likely, though.

The pes of the Neandertal mans:

Interestingly, the groundss reveal that the opposability of the large toe might be someplace between the modern worlds and the life apes. Others deny it, because of the more human features in the tarsometatarsal articulation, which can be varied on a great graduated table even in modern worlds. Typical Neanderthal characteristics are the short proximal phalanx of the large toe and the short cervix of the scree.

The possible marks of the bipedalism in the fossil groundss:

Apart from the castanetss of the pes other skeletal remains can uncover the erected organic structure position and the possible bipedal walking wonts. A comparative longer arm may be a mark of the arborical life-style, or partially arborical life fortunes. However, Lucy has comparatively short fingers, non ape-like, long 1s ( JOHANSON-EDEY 1990 ) The form of shoulder blade and the orientation of the glenoid pit besides can assist to reply this inquiry. A little fragment of an Australopithecus afarensis shoulder blade suggests that its proprietor had a more ape-like in this inquiry, than human like. In apes the glenoid pit faces towards the braincase and this characteristic can be observed besides in instance of this fragment. A more complete shoulder blade – which derives from an A. africanus ( Sts 7 ) – can state us more inside informations about the possible maps of the thoracic girdle. This scapula looks really similar to the scapula fragment of the afarensis specimen ( AL 288-1l ) , and they both bear more similarities to the thoracic girdle of the apes, particularly to the orang-utans. The ribcage has more ape-like features in its visual aspect. The form of the vertebral column, nevertheless, widens distally ( the lumbar vertebrae are the widest ) as it appears in worlds, which is another possible mark of the two-footed motive power. The pelvic girdle shows more groundss for the mosaic morphology yet once more. The iliac crest is instead human-like, although it is more extended laterally and the cotyloid cavity orients more anteriorly. Possibly this is the ground why A. afarensis has a comparatively really long femoral cervix. The iliac blades direct interiorly, as good. The form of the sacrum is really broad – another human-like mark, nevertheless its posterior section is non as curved anteriorly as it is in the modern worlds.

Harmonizing to Johanson ( JOHANSON-EDEY 1990 ) , Lucy ‘s pelvic girdle is adapted to the two-footed motive power every bit good as to the possibility to give life to large-headed babes, as her pelvic girdle is so broad.

All these characteristics make likely that the A. afarensis could walk bipedally, but in a more complicated manner. The anteriorly faced cotyloid cavity could ensue a really heavy bipedalism. On the femoral caput, we can detect a stronger fovea than it is on the femoral caput of the modern homo.

In quadrupeds the tibial tubercle is more rounded and less crisp. The “ acuteness ” of the tibial tubercle is a more human ( or bipedal ) feature. This acuteness can be observed in Lucy, although her tibia looks more robust compared to the really tall juvenile, the Turkana male child ( H. erectus ) .

In proximal thighbone of the Australopithecines, there are about the same figure of similarities to worlds ( the varied presence of the intertrochanteric line and the Obturator externus channel ) than to Pan troglodytess ( the little femoral caput and the non-flaring greater trochanter ) and the alone characteristics ( long femoral cervix, compressed femoral neck-cross subdivision ) , the more similarities to worlds in the inquiry of the distal thighbone ( the high/very high bicondylar angle, the egg-shaped shaped sidelong epicedial profile ) , and its ain alone phenomena in the epiphysis form and symmetricalness, but the femoral shaft ‘s more similarity to the Pan troglodytess gives us a really eclectic feeling about the possible motive power of the Australopithecines.

As I wrote in the 1B inquiry, the pes of the Australopithecines show really varied image every bit good. It reveals both human and ape like characteristics – such as about everything else in the Australopithecus skeleton. The more human like elements of the pes include the human-like mortise joint articulation, the ability of a better dorsiflexion, the expanded base of the 5th metatarsal, the broad heelbone and the presence of the longitudinal arch.

On the other manus, there are several ape-like features, like the form of the phalanges, the tubercle of the calcaneous has an egg-shaped orientation, besides has a immense peroneal tubercle, the already mentioned ape-like form of the “ hook ” of the sidelong cuneiform bone, and the rounded caput of the first metatarsal.

Summarizing, the mosaic morphology in the Australopithecines are really strongly present, they portion similarities to the worlds, every bit good as to the apes, but they besides developed ain characteristics. It is really likely that they were adapted to the two-footed motive power, but non in a modern human manner.

The essay has been written by utilizing the undermentioned books as a guide-line:

Aiello and Dean, 2006: An Introduction To Human Evolutionary Anatomy, reprinted in 2006, Elsevier Academic Press, London

The stuffs during the Demo-sessions

And

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