WEEK 5 Discussion Forum--Anthropology 1( need high quality assignment!! And due on time !!!)
Ivylee715
CHAPTER 8 Primate and Hominin Origins
Dating Methods • Relative dating methods tell you that something is older or
younger than something else
• Stratigraphy- based on the law of superposition, which states that a lower layer is older than a higher one
• Biostratigraphy: Using comparative fossils, mainly predictable dentition, that have been dated at one site to date another
• Paleomagnetism: Using magnetically charged particles in deposits to determine the earths magnetic poles at time of deposit • This method is used primarily as a double check in conjunction
with other methods
Dating Methods
• Chronometric (Absolute) dating methods are based on
calendar years
• K/Ar, or potassium argon method used to date materials
in the 5-1 mya range
• Carbon-14 method used to date organic material extending
back to 75,000 years
• Uranium series dating
• Thermoluminescence
• Electron spin resonance (ESR)
Early Primate Evolution
• The beginnings of the primate order date to the
initial placental mammal radiation at least 65 mya.
• The earliest primates date to the Paleocene (65-56
mya) and diverge from quite early primitive
placental mammals, called plesiadapiforms.
• A vast number of fossil primates from the Eocene
(56–33 mya) have been discovered and now total
more than 200 recognized species.
Eocene Primates • Fossil primates from the Eocene display distinctive primate features.
• North Africa fossils dating from the early Eocene (50 mya) and Egypt (37 mya)
• Some may have been ancestral to the lemurs and lorises, or the tarsiers, evidenced by a dental comb
• Most do not appear to be ancestral to any living primate
• When the Eocene primates in their entirety are examined, it is certain that they were:
1. primates,
2. widely distributed, and
3. mostly extinct by the end of the Eocene
• Darwinius, from the
Messel site in
Germany, discovered in
2009 and dates to 47
mya. Though initial
claims to connection to
living primates were
made, they have yet to
be confirmed and are
hotly debated
Oligocene Primates
The Oligocene (33–23 mya) has yielded fossil
remains of several species of early anthropoids.
By the early Oligocene, continental drift had separated
the New World from the Old World.
The earliest anthropoids may have reached South
America by “rafting” over from where they emerged in
Africa.
The ancestry of New and Old World monkeys was
separate after 35 mya.
Oligocene Primates from Fayum
• Apidium: Early primate genus found in the Fayum, a region
in Egypt
• Primitive dental arrangement suggests near or before
evolutionary divergence of Old and New World anthropoids
• Small, squirrel-like fruit and seed eating, adept at leaping and
springing
Oligocene Primates from Fayum
• Aegyptopithecus
• Largest of Fayum anthropoids, roughly the size
of a modern howler monkey (13-18 lbs)
• Short-limbed, slow-moving
• Bridges the gap between
Eocene fossils and succeeding
Miocene hominoids
Miocene Fossil Hominoids
• Existed for the entirety of the Miocene, 23 to 6mya
• Thousands of fossils have been discovered, many of
which only tenuous or disputed conclusions have
been drawn
• Geographically widespread with fossils discovered
across Africa, parts of Europe and Asia
Miocene Fossil Hominoids
African forms (23–14 mya)
Found primarily in Western Kenya, these have many
primitive characteristics.
Proconsul
Apelike derived teeth, but postcranially resembles a
monkey
Miocene Fossil Hominoids Asian forms (16–7 mya)
• The largest and most varied group found from Turkey through India/Pakistan and east to southern China, most are highly derived.
• Sivapithecus
• Found in Turkey and Pakistan
• Facial features similar to the modern orangutan, suggesting a fairly close evolutionary link.
Sivapithecus Compared
• Comparison of a modern chimpanzee (right), Sivapithecus (middle), and a modern orangutan (left).
• Both Sivapithecus and the orangutan exhibit a dished face, broad cheekbones, and projecting upper jaw and incisors.
Miocene Hominoid Fossils Conclusions
• Mostly large-bodied hominoids, similar to
orangutans, gorillas, chimpanzees, and humans not
siamangs and gibbons.
• Most forms discovered are so derived that they are
probably not ancestral to any living form. (except
Sivapithacus)
• Definite hominins from the Miocene has not been
indisputably confirmed. Some finds suggest that
hominins diverged sometime in the latter Miocene.
Who are the Hominins?
• Name for all members of the tribe Hominini
• Includes all bipedal hominoids back to the divergence with
African great apes.
• Refers to all great apes (orangutans, gorillas, chimpanzees,
and bonobos) and humans
• Defined by dental features, bipedal locomotion, large brain
size, and tool making behavior
• Characteristics that developed at different rates, called
mosaic evolution
Mosaic Evolution
• A pattern of evolution in which the rate of evolution in one
functional system varies from that in other systems.
• In hominin evolution, bipedal locomotion is a defining
characteristic; other features such as brain development
and behavior become significant in later stages
• In other words the traits that make us human did not all
evolve at the same time, and different species evolved at
different rates with different traits
Traditional Classification of Hominoids
Revised Classification of Hominoids
Paleoanthropology
• Paleoanthropology is defined as the study of early
humans.
• Paleoanthropologists reconstruct the anatomy,
behavior, and ecology of our ancestors:
• It is a diverse multidisciplinary pursuit seeking to
reconstruct every bit of information possible
concerning the dating, anatomy, behavior, and
ecology of our hominin ancestors.
• Locate early hominin sites, collect faunal remains
and artifacts
Early Hominin Tools
• Earliest tools likely made of perishable materials
• Hominin bipedalism would have made tools easier to
transport
• Oldowan-Earliest recognized stone tool culture, including
very simple tools, mostly small flakes
Hominin Bipedalism
• Habitual bipedalism, efficient and standard bipedal locomotion is seen only in hominins.
• Hominins are also obligate bipeds, meaning they cannot locomote efficiently in any other form
• Advantages of bipedalism:
• Freed the hands for carrying and tool use
• Offers a wider view of surroundings.
• Bipedal walking is an efficient in covering long distances.
Obligate Bipedalism: Structural Alterations
• Foramen magnum positioned under the skull to balance
the skull and enable the head to be held upright
• Two distinctive curves in spine to keep weight centered
above pelvis
Obligate Bipedalism: Structural Alterations
• Pelvis is comparatively much shorter and broader and extends
around to the side, stabilizing the line of weight transmission
from lower back to hip joint, supporting internal organs in
upright posture
Obligate Bipedalism: Structural Alterations
• Foot as stable support instead of a grasping limb
• Elongated legs to increase the length of stride
• Full extension of knee and narrow stance to maintain center of
support directly under the body
Finding Early Hominin Fossils
• East Africa sites along the Great Rift Valley where more than
2,000 hominin fossils have been found
• South Africa sites with geological strata more complex than
along the East African Rift Valley
Possible Early Hominins
• These are grouped as the Pre-Australpiths
• They are classified as homimin, but it’s disputed by some
• Sahelanthropus tchadensis
• Small braincase and huge browridge
• Intermediate foramen magnum
• Vertical face, hominin like teeth
• No post-cranial remains to prove locomotion
• Ardipithecus
• Ardi, a female skeleton is 50% complete, earliest hominin to have
so many parts of the body preserved
• Pelvis and foot show both derived and ancestral characteristics
• Divergent big toe shows high climbing ability and life
adapted to the trees
Orrorin Tugenensis
• First hominid with preserved post cranial remains
• Best evidence among the Pre-Australiths for bipedalism
• Dated to 6mya
Australopiths (4.2–1.2 mya)
• The group of well studied, diverse and widely distributed of the early African hominins are called australopiths.
• This group of hominins is made up of two closely related genera: Australopithecus and Paranthropus.
• Existed over a 3 million year time range from approximately 4.2 mya until becoming extinct apparently close to 1 mya.
Australopiths (4.2–1.2 mya)
• Major features
1.They are all bipedal though not necessarily the
same as Homo
2.They all have relatively small brains at least as
compared to Homo.
3.They all have large teeth, particularly the back
teeth, with thick to very thick enamel on the
molars.
Australopithecus afarensis
• Found primarily at Hadar, Ethiopia and Latoli, Tanzania
• Primitive in relation to later Australopiths
• Very sexually dimorphic
• Obligate and habitual bipeds that were still capable of climbing
• Evolutionary bridge between early pre-Australopiths and the
later hominin species
Laetoli footprints
• Dated at between 3.5 and 3.7 mya.
• Fossilized hominin footprints were found in an ancient volcanic
bed in Laetoli, Tanzania.
• Despite agreement that these individuals were bipedal, some
researchers feel they were not bipedal in the same way as
modern humans.
Note the deep impression of the heel and the large toe in line (adducted) with the other toes.
Infant A. afarensis skeleton • A mostly complete female infant
A. afarensis skeleton was announced in 2006.
• The discovery was made at the Dikika locale in northeastern Ethiopia, near the Hadar sites.
• Dated to 3.3 mya.
• First immature hominin prior to 100,000 ya
• Key to developmental study
Later More Derived Australopiths (2.5–1.2 mya)
• Over time australopiths became adapted to varied niches, became more derived and showed physical changes making them distinct from their immediate ancestors.
• There were at least three separate lineages of hominins living between 2.5 and 1 mya.
• Australopithecus
• Paranthropus
• Homo
Paranthropus
• Very derived australopith
• Displays features characteristic of a varied and tough diet
• Massive teeth
• Large jaws and sexually dimorphic sagittal crest
• Small brain capacity
• Large, broad, flat face
• Two species:
• Paranthropus boisei: Very dentally
robust specimens from East Africa
• Paranthropus robustus: Less dentally
robust species from South Africa
Austrolpithicus africanus
• Dated to 3 and 2 mya
• Discovered in South Africa
• The Taung child, discovered in 1924
• Well preserved child's skull
• Small relative braincase
• Large teeth, but reduced from Paranthropus
• Clear markers for obligate bipedalism
Austrolpithicus sediba
• Considered by initial reports to be transitional between the
australopiths and early Homo, but contested by others
• Dated to less than 2mya
• Early Homo remains have been dated earlier leading to the
challenges to the A. sediba lineage claims
• Austrlopith charactristics;
• Small brain
• Long arms, curved fingers
• Primitive foot features
• Homo characteristics
• Very derived hand
• Possible brain changes
Early Homo (2.0+-1.4 mya)
• Evidence suggests at least one, possibly two species lived
in East Africa for at least a million years.
• One lineage likely evolved in H. erectus, the other went
extinct
• Homo habalis remains have been discovered in Turkana
and Olduvai and are the best known early Homo species
• Early Homo show:
• Significantly increased brain size
• Associations with stone tools
• Skull shape unlike the australopiths
• Face shape and teeth still robust
Homo naledi • Dicovered in 2013
• Over 1500 fossils found in the Dinaledi Chamber in the Rising
Star cave system representing at least 15 individuals
• Largest collection of a single species ever found in Africa
• Full age range from infants to adults have been found
• Unique mix of australopith and Homo characteristics
• Small brain, trunk, pelvis and femur similar to australpiths
• Cranial shape, hands and feet close to Homo
• Remains may have been intentionally placed
• Not yet dated
Three Options for Dating H. naledi
What’s the Big Picture • Even with new finds all the time there will always be gaps in the
fossil record, it may always be incomplete
• There are patterns to be found:
• Early hominin species had restricted ranges, this can lead to rapid
speciation from population isolation
• Most species appear to have been at least partially tied to arboreal habitats
• Some (mainly Paranthropus) diets of coarse, fibrous plant foods, such as
roots may have routinely taken them farther away from the trees and led to
divergence
• Very little evidence for an evolutionary trend of increased body size or of
markedly greater encephalization except for some early Homo
• No association of any pre-australopith or australopith hominins with
patterned tool use
• All early African hominins show an accelerated developmental pattern like
the great apes, one quite different from Homo sapiens