Australopithecus

Question 1

Australopithecus afarensis

Answer 1

• Between 3.9 and 2.9 MYA
• A. afarensis was slenderly built, like the younger Australopithecus africanus.
• A. afarensis is thought to be more closely related to the genus Homo (which includes the modern human species Homo sapiens), whether as a direct ancestor or a close relative of an unknown ancestor, than any other known primate from the same time.
• The most famous fossil is the partial skeleton named Lucy (3.2 million years old) found by Donald Johanson in Ethiopia

Question 2

Australopithecus Afarensis Primitive features

Answer 2

• Sexual dimorphism- males have much larger body sizes than females
• Small brain size (~450 cc)
• Relatively long arms although still shorter than a chimpanzee
• Finger and toes that are longer and more curved than a human (yet shorter and less curved than a chimpanzee)

Question 3

Australopithecus Afarensis Derived features

Answer 3

• A barrel-shaped ribcage
• A relatively flexible lumbar region with a lumbar curve
• A short and broad pelvis with a wide sacrum
• A bicondylar angle or carrying angle of the knee
• Stiff feet with arches

Question 4

Lucy - AL 288-1

Answer 4

• Lucy was discovered in 1974 in Ethiopia by Donald Johanson.
• Several hundred pieces of bone fossils representing 40 percent of the skeleton.
• Female.
• 3.2 MYA
• The skeleton presents a small skull akin to that of non-hominin apes, plus evidence of a walking-gait that was bipedal and upright, akin to that of humans (and other hominins); this combination supports the view of human evolution that bipedalism preceded increase in brain size.

Question 5

Australopithecus afarensis Skull

Answer 5

• Compared to the modern and extinct great apes, A. afarensis has reduced canines and molars, although they are still relatively larger than in modern humans.
• Relatively small brain size (about 380–430cm3).
• Prognathic face (when compared to apes).

Question 6

Australopithecus afarensis Pelvis

Answer 6

• Pelvis is far more human-like than ape-like.
• The iliac blades are short and wide.
• Sacrum is wide and positioned directly behind the hip joint.
• Strong attachment for the knee extensors is clear.
• While the pelvis is not wholly human-like, these features point to a structure that can be considered radically reshaped to accommodate a significant degree of bipedalism in locomotor repertoire.

Question 7

Australopithecus afarensis Femurs

Answer 7

• Femur angles in toward the knee from the hip.

- Allowed foot to fall closer to the midline of the body, and is a strong indication of habitual bipedal locomotion.

Question 8

Australopithecus afarensis Feet

Answer 8

• The curvature of the finger and toe bones (phalanges) approaches that of modern-day apes, and is suggestive of their ability to efficiently grasp branches and climb.
• Loss of an abductable great toe and therefore the ability to grasp with the foot (a feature of all other primates) suggests A. afarensis was no longer adapted to climbing.

Question 9

Lucy and chimpanzees share:

Answer 9

• Elongated skull with small brain case
• Face and jaws that jut out from the brain case
• Shoulder blades and joints that are suited for climbing trees

Question 10

Lucy and humans share:

Answer 10

• Spine connection beneath the skull to keep the head steady
• Robust and broad basin-shaped pelvis to support the upper body and hold it upright
• Angled thigh bones that place the weight directly over strong knee joints
• Compact and archer feet that support the full body weight with each step

Question 11

Australopithecus afarensis Hands

Answer 11

• Gracile hands – fine motor coordination/skill.
• Curved phalanges – arboreality?
• Wrist-locking mechanism, might suggest they engaged in knuckle-walking.

Question 12

Australopithecus africanus

Answer 12

• 3.3 and 2.1 MYA (late Pliocene and early Pleistocene).

- Gracile build.

Question 13

The Taung Child

Answer 13

• 1924 - Raymond Dart - Interested in fossils found in limestone quarry at Taung, South Africa.
• Skull of an ape-like fossil: human traits (eye orbits, teeth, and, most importantly, ventral position of foramen magnum).
• Australopithecus africanus

Question 14

Australopithecus Sediba

Answer 14

• Discovered by Lee Berger in 2013, South Africa
• From early Pleistocene, approx. 2 MYA.
• The fossils were found together at the bottom of the Malapa Cave, where they apparently fell to their death, and have been dated to between 1.977 and 1.980 million years ago
• Juvenile male (MH1 also called “Karabo”, the holotype) - unarticulated, 34% complete
• Adult female (MH2, the paratype) – partial articulation, 46% complete
• Australopithecus sediba may have lived in savannas but ate fruit and other foods from the forest—behaviour similar to modern-day savanna chimpanzees.
• The conditions in which the individuals were buried and fossilized were extraordinary, permitting the extraction of plant phytoliths from dental plaque.

Question 15

Australopithecus sediba: A Transition between Australopithecine and Homo?

Answer 15

• Wide range of mosaic features exhibited in both cranial and post-cranial morphology
• Cranial capacity of MH1, estimated to be at 95% of adult capacity (420cm3), is at the higher end of the range for A. africanus and far from the lower range of early Homo (631cm3).
• Mandible and tooth size are quite gracile and similar to what one would expect to find in H. erectus. However, the cusp spacing is more like Australopithecus.
• Some suggest that A. sediba may be a transitional species between the southern African A. africanus (the Taung Child, Mrs. Ples) and either Homo habilis or even the later H. erectus (Turkana boy, Java man, Peking man).