Chapter 11

Question 1

Primitive Traits

Answer 1

Traits that are more like the common ancestor we share with modern large-bodied hominids.

Question 2

Modern Traits

Answer 2

Traits that are unique to humans (Homo sapiens).

Question 3

Sagittal Crest

Answer 3

A crest on the top of the skull of chimpanzees that helps muscles and ligaments attach to the jaw. Chimpanzees have this trait to allow stronger chewing action than we have as we don’t have a sagittal crest.

Question 4

Brow Ridge

Answer 4

A mostly primitive trait that is caused because of the skull going straight back rather than taking on a more vertical protrusion like humans do. Not necessarily adaptive and some people may have a slight brow ridge, but not to the extent of any ape nearly. Meaning, we don’t not have a brow ridge, but rather it’s more embedded in our skull because of shape.

Question 5

Prognathism

Answer 5

The physical trait of the face or snout is rather elongated. Humans do not really have this trait therefore it is more primitive.

Question 6

Primitive Traits

Answer 6

1. High degree of prognathism (projection of the snout are of the face).
2. Large brow ridges
3. Sagittal crest
4. Large mandible
5. Large canines/teeth in general
6. Small cranial capacity
7. Large nasal cavity
8. Flattened cranial base
9. Ovular skull shape.

Question 7

Modern Traits

Answer 7

1. Little to no prognathism
2. Little to no brow ridges
3. Small mandible
4. Small teeth
5. Smaller nasal cavity
6. Large cranial capacity
7. High, vertical forehead
8. Rounded back of cranium (occipital bone).
9. Globular skull shape
10. Chin

Question 8

Sahelanthropus Tchadensis ( 7 million years ago).

Answer 8

The oldest early hominid fossil found in Africa. (Note: there is no evidence of bipedality in the fossil so the actual question as to whether this creature was in fact a hominid is greatly called into question and it is debated as to whether it should be dubbed a hominid).

Question 9

Orrorin Tugenensis ( 6 million years ago).

Answer 9

A bunch of bones especially some almost complete lower limb bones theorized to belong to early hominids. These remains seem to have clear evidence of bipedality.

Question 10

Ardipithecus Ramidus (4.4 million years ago).

Answer 10

A large fossil assortment with many dental specimens, upper bone, fragmentary cranial remains, and one specimen that is 40% of a complete skeleton.

1. Foramen Magnum positioned further forward
2. Very prognathic face
3. Flattened cranial base
4. Thin enamel caps on the molars.
5. Humerus indicates not weight-bearing which means bipedality
6. Legs indicate obligate bipedalism
7. Estimated body weight 93 lbs (similar to other early hominids and chimps).

Question 11

Australopithecus

Answer 11

1. They all were clearly bipedal (securely included in the hominid family).
2. They all have relatively small brains, as compared to modern humans.
3. They all have large teeth, particularly the molars, with thick to very thick enamel, similar to the great apes.

Question 12

Laetoli, Tanzania

Answer 12

A place in which a trail of hominid footprints were fossilized in volcanic ash. This 70 meter trail was found by Mary Leakey’s expedition in Laetoli, Tanzania in 1978. This showed evidence of clear bipedality, was dated by K/Ar and was found to be 3.6 million years ago.

Question 13

Australopithecus Afarensis (“Lucy”) ~3.7 - 3 million years ago.

Answer 13

Around 40% of a skeleton found in Ethiopia nicknamed Lucy by the archaeologist who found her.

1. Brain size 420 cc not much larger than chimps
2. Significant prognathism
3. Large brow ridges
4. Sagittal crest
5. Flattened cranial base and base ridge.
6. Large pointed canines.
7. dental arcade smaller, but very u shaped, like chimps.
8. has the correct location of the foramen magnum to indicate obligate bipedality.
9. Has the correct pelvic shape & femur angle for obligate bipedality.
10. Very short: 3 1/2 to 4 feet tall.
11. High degree of sexual dimorphism
12. Upper limbs are proportionally longer than humans like modern apes.

Question 14

Foramen Magnum

Answer 14

The whole in the skull that the spinal column goes through to connect with the brain.

Question 15

Australopithecus aethiopicus (2.4 million years ago).

Answer 15

1. Extra large brow ridges
2. Huge sagittal crest
3. Brain size 410 cc similar to A. Afarensis
4. Flattened cranial base
5. Like all other australopithecines foramen magnum indicates clear bipedality.
6. Very prognathic face (more than A. Afarensis but less than chimps).

Question 16

Australopithecus Africanus(3.3 - 1 million years ago).

Answer 16

1. small brain 405 cc: Adult 440 cc
2. “The Taung Child” (3-4 years old.)
3. Forehead does not recede as much as apes or other australopithecines
4. very small canines
5. molars are very large & broad
6. Foramen magnum further forward than apes less than humans, probably bipedal.

Question 17

Gracile Australopithecines

Answer 17

More delicate, a little more modern features pretty much only applies to A. Africanus

Question 18

Robust Australopithecines

Answer 18

More robust or heavy features, more primitive, with variation in the amount of robusticity.

1. Postorbital constriction
2. Marked sagittal crest
3. Broad cheekbones
4. Megadont dentition (huge molars), very coarse diet.
5. Heavy brow ridges and cranium
6. Small incisor and canine teeth.
7. Marked sexual dimorphism
8. Definite bipedalism, likely less arboreal than less robust australopithecines.

Question 19

Australopithecus Robustus ( 2 - 1 million years ago).

Answer 19

1. Market sagittal crest
2. Heavy brow ridges
3. Heavy cranium in general
4. small incisors & canines
5. Marked sexual dimorphism
6. Broad cheekbones
7. Megadont (large molar teeth).

Question 20

Australopithecus Boisei (2.4 - 1.2 million years ago).

Answer 20

1. Heavy brow ridges
2. Marked sagittal crest
3. Megaodont (large molar teeth)
4. Broad cheekbones
5. Small incisors & canines
6. Huge mandible

Question 21

Postorbital constriction

Answer 21

Narrowing of the braincase behind the eye orbits.

Question 22

Early Hominid Trends

Answer 22

1. They had very restricted ranges or territories. Each species exploited a small area that could have been easily isolated from other populations of its own species, leading to speciation.
2. Despite obligate bipedalism, most early hominid species at least partially tied to arboreal habitats, keeping them more adapted to these environments than modern humans are.
3. Little to no trend toward increased body size or of markedly greater encephalization (increase in brain size). Relative brain size increased by no more than 10-15% over a period of 3 million years. Tied to this, no clear association of any of these hominids with sophisticated stone tool manufacture.
4. An accelerated developmental pattern (reaching adult maturity quickly), similar to apes and different than the delayed developmental pattern characteristic of humans.