Compare the overall curvature of the modern human and great ape vertebral column. What differences do you see? If early hominins had an L5 similar to modern humans, what would you estimate the vertebral column to look like in these animals?Explain

Evolution of the Human Skeleton
Comparative Anatomy of the Axial Skeleton, Arm, and Hand

Use eSkeletons to compare the lumbar vertebrae of great apes and modern humans. What differences do you see? In particular, pay attention to the last lumbar vertebra. Which specimen displays a vertebral body that significantly shortens posteriorly? This anteroposterior “wedging” is a distinct feature of modern humans and helps maintain the lumbar lordosis. What behavior is the L5 “wedging” most-likely related to?

Compare the overall curvature of the modern human and great ape vertebral column. What differences do you see? If early hominins had an L5 similar to modern humans, what would you estimate the vertebral column to look like in these animals?

Compare the overall shape of the modern human and great ape rib cages. Which of these thoracic shapes is seen in early hominin specimens such as A. afarensis (“Lucy”)? Why, in part, does thoracic shape differ between great apes and modern humans?

Below is a reconstruction of the glenoid fossa in an early hominin (Australopithecus afarensis, “Lucy”). Compare the orientation of the glenoid fossa in a modern human, great ape, and early hominin. What differences do you see? Is the early hominin glenoid fossa more similar to modern humans or African apes?

Use eSkeletons to observe the distal humerus in modern humans and great apes (distal, dorsal, ventral, anterior, and posterior views). What differences do you see? Pay particular attention to the lateral side of the distal humerus, both anteriorly and posteriorly. Which group has a more prominent lateral edge to the trochlea and olecrenon fossa? Which group has a larger and superiorly extending lateral epicondyle? Do modern humans or African great apes have a deeper olecranon fossa? What unique locomotor behavior in African apes might these features relate to and why?

There are few complete forelimb bones in the early Plio-Pleistocene fossil record. The bones that exist are generally unassociated and are variable in morphology. We have representatives of 3 Plio-Pleistocene humeri here: KNM-KP 271, TM 1517, and SDR-037 (see below). Compare these specimens and describe the distal humerus in terms of similarities and differences to apes and modern humans. Which specimen looks more African-ape like? Which looks most like a modern human? Name some features to support your argument.

Use eSkeletons to compare the proximal ulna in modern humans and African apes. Compare the coronoid process in the two groups. Do humans or African apes have a larger coronoid process? Now compare the olecrenon process in African apes and humans. Do humans or African apes have a longer, more proximally extending olecranon process? Unfortunately, very few ulnae and radii exist that can be positively associated to early hominin taxa.

Use eSkeletons to compare the African ape hands with the human hands. Examine the metacarpals in various views (palmer, medial, lateral, dorsal), paying close attention to differences near the head of the bone. Pay particular attention to the dorsal surface of the metacarpal heads. What differences do you see? What locomotor behavior might these features relate to? Are these features found in known early fossil hominins?

Below is a diagram illustrating phalangeal curvature in an early hominin (A. afarensis “Lucy”), great apes and humans. What differences do you notice in the shape of the phalanges between African apes and modern humans? Which group has more curved phalanges? What behavior might phalangeal curvature be related to? What condition is seen in early hominins? What might this suggest about their locomotor repertoire?

Use eSkeletons again to look at the thumb bones in modern humans compared to African apes. Pay particular attention to the length of the thumb compared to the other digits in both groups. Which group has a relatively longer thumb? From what is known of the A. afarensis hand, it would appear that early hominins had a thumb length more similar to modern humans.

Early hominins do not display any of the typical features associated with knuckle walking in African apes such as expanded metacarpal heads, dorsal ridges on the metacarpal heads, or the well-defined dorsal ridge found on the distal radius. However, a few other features in the African ape distal radius have been suggested to be related to knuckle-walking: the distal extension of the dorsal ridge of the radius and the angle of the radial articulation with the scaphoid and lunate.

Are these features present in early hominins? If so, could these features indicate that early hominins evolved from a knuckle-walking ancestor? Why or why not? Compare the specimens in the figure below. Recently, researchers have argued that the supposed knuckle-walking features in the African ape carpal bones do not seem functionally related to knuckle-walking. Additional readings on this topic can be found on blackboard (Richmond et al 2001, Tallman 2012).

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