chapter 19

Robust Australopithecines trend

- relatively restricted geographic range. They are found in disparate areas, meaning they were likely very specialized for certain kinds of habitats. - They were bipedal, but likely not as efficient at bipedalism as species that come later. - No great increases in brain/body size - Rapid growth and development (unlike humans)

Australopithecus Robustus

2.0 - 1.5 mya South Africa Sagittal Crest Massive flat face, forward projecting zygomatics Large molars, small incisors Thick enamel with more pits (harder foods than A. africanus) High sexual dimorphism (males taller and heavier) Lifespan around 17 years

australopithecus boisei

2.3-1.2 mya in east africa Homo habilisand Homo erectus also in east Africa during the same time period. high level of sexual dimorphism (females less robust, shorter and lighter) A. boisei is descended from A. aethiopicus, continuing a trend in this particular lineage towards hyper-robusticity. They share many of the same features with aethiopicuslike the flaring zygomatics, large sagittal crest, and large molars with thick enamel, but these features are even more emphasized in this species than the last. This means that boisei was becoming even more specialized to fit their niche.

Australopithecus afarensis

3.0-3.7 MYA. Lucy is a well known fossil Small brain, prognathic face. Had a slightly more parabolic dental arcade than previous hominins. Definitely bipedal but had some arboreal adaptations like curved phalanges

first toolmakers

3.2-3.4 mya, cut marks on animal bones in dikika region of europe. evidence of butchering antelopes and bones broken to get bone marrow 3.3 mya: oldest stone tools found in kenya created by knapping (hitting stones together to strike off sharp flakes)

Australopithecus anamensis

3.9-4.2 MYA large canines, intermediately sized molars, thick enamel, U-shaped dental arcade (primitive/ape-like) on post-cranial remains we see some derived traits associated with bipedalism (thickened tibial plateau; supports more weight in bipedal locomotion)

Lucy

A forty percent complete skeleton discovery of an Australopithecus afarensis, or a species within the category of hominid. She was rediscovered on November 24, 1974 in Hadar, Ethiopia. 3.5 feet tall, adult 11-12 years broader and wider and more bowl-shaped than a chimp pelvis but not as effective as human

Australopithecus africanus

A gracile australopithecine from South Africa and lived 2.5-3.3 MYA Less prognathic face with smaller teeth and very reduced canines. Clearly bipedal with human-like pelvis and S-shaped spine. Straight phalanges!! So they were relying less on arboreal traits and focusing on terrestrial bipedalism. Slightly larger brain.

laetoli footprints

Associated with A. afarensis. Footprints of at least 2 individuals, from 3.6 mya. Show the strides with bones and tissues. Footprints is similar to ours, even with adducted hallux. A double arch and rounded heel in foot as well! Clearly social, traveling together

Selam

Dikika child, 3 year old female child A. afarensis skeleton. Still had some arboreal tendencies. - The scapula is upwardly rotated compared to that of a human. This means that afarensis was still likely partially arboreal, as this is a trait adapted to brachiation. - presence of the hyoid bone. The hyoid is a floating bone in the throat to which the base of the tongue anchors. Because of this, its morphology is very important for speech. The hyoid bone of this individual is morphologically more similar to apes than humans, so we can infer that australopithecines probably weren't capable of speech.

Taung Child

First hominin fossil found in Africa in 1925. ~3 years old Thought to have been killed by an eagle; other australopithecine remains have been found in hyena dens, or with leopard tooth marks.

gracile australopithecines

Members of the genus Australopithecus possessing a more lightly built chewing apparatus; likely had a diet that included more meat than that of the robust australopithecines. Found in south and east africa. 4-1 mya. Bipeds. Small brained and small bodied A. anamensis A. afarensis A. africanus A. garhi

Nutcracker Man

Robust Australopithecus boisei. Sagittal crest; adaptation for heavy chewing; HUGE molars, large face, lived in a dry savannah/woodland habitat. Large face with sexual dimorphism

zygomatic bones

bones on the side of our face that form the cheeks. In the robust australopithecines, the zygomatic bones flare out dramatically, causing their face to appear very wide in comparison to the graciles. While this allows extra room for the enlarged chewing muscles to pass underneath them, it also has a buttressing effect on the face that supports it with the increased power and force coming from the jaw.

dietary hypothesis

gracile: larger anterior teeth --> omnivores -- tooth movement: crushing -- microwear: complex robust: deep jaws, large cheek teeth --> hard seeds and nuts (heavy reliance on grasses, need lots of grinding) -- tooth movement: shearing -- microwear: simple

nuchal crest

large raised crest across the back of the skull on the occipital bone that is also a large muscle attachment an attachment for the muscles of the neck and back, and its prominent size in the robusts would have helped counteract the huge amount of force that was happening at the front of the skull.

Australopithecus aethiopicus

lived right around the time of the adaptive radiation event, from 2.7 to 2.3 MYA east africa lived at the same time as A africanus and A garhi

Australopithecus garhi

most likely candidate for the link between the australopithecine and homo genera. lived about 2.5 MYA, smaller teeth and more gracile. arm-leg ratio was more human like and have been found in association with primitive stone tools as well as butchered animal bones

sagittal crest

ridge of bone almost like a mohawk following the sagittal suture on the skull. Looking at the side view and the top-down view, of the robust australopithecine, you can see this is where the large chewing muscles attach and anchor down to provide a ton of power.

true

t/f - Lucy had a bicondylar angle of the femurs, bringing center of gravity beneath the pelvis. This allows them to walk without a swaying motion. - Wider and more flared pelvis than human. Not as efficient. - Arms relatively longer to body and upwardly rotated scapula so arboreal adaptation

true

t/f australopithecine were likely prey animals. small, ~3ft tall and didn't have much defense so lived in a group for protection used bone tools for scavenging

true

t/f in gracile australopithecines, anterior teeth are more emphasized and the premolars/molars are much smaller but in robust australopithecines, they have megadontia (gigantic teeth) and mostly have chewing teeth (premolars/molars)

true

t/f robust lineage went extinct about 1 MYA. Homo lineage came into the scene and were more flexible (general diet) and adaptable. bigger brains and more bipedally efficient and had tools for digging and stuff

true

t/f robust species are descended from gracile australopithecines. This tells us that during the adaptive radiation event, there were some niches that favored more gracile features, and some that favored more robust features.

false

t/f the robust australopithecines have modern descendents

false

t/f there are more differences between robust and gracile australopithecines other than difference in skull size

robusticity of the skull

the one big difference between gracile and robust australopithecines This is because the robust species skulls are emphasized where chewing muscles are attached. Look at the large sagittal crest on the individual on this slide as well as the large nuchal crest around the back of the skull. This is due to their different diets -the gracile species ate much softer foods compared to the robust species.

Robust Australopithecines

three known species of these, known for their robust cranial features with large muscle attachments, dense bone, and powerful dentition. We will cover Australopithecus aethiopicus, A. boisei, and A. robustus.

The black skull

turned black after sitting in manganese-rich soil for millions of years. It shares a prognathic face and a similar small brain capacity, around 410 cc with its ancestor afarensis. the features that make it truly distinct from its gracile ancestor are the derived, hyper robust features. These include widely flaring zygomatics, a large sagittal and nuchal crest, and huge molars with very thick enamel.