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Lecture

ANT203 - January 10 2012.pdf


Department
Anthropology
Course Code
ANT203Y1
Professor
Xueda Song

Page:
of 5
Dating (chapter 10)
Paleoprimatologist: a person who specializes in the study of the nonhuman primate fossil
record
Paleoanthropologist: a person who specializes in the study of ancient humans; a
multidisciplinary endeavour including geologists, archaeologists, physical anthropologists
and paleoecologists
Interpreting fossil remains
1. Geological knowledge / relative dating (stratigraphy, paleoenvironments, plant/
animal fossils)
2. Absolute Dating techniques (carbon, uranium, K/Ar)
3. Statistical analysis (application of computerized phylogenetic techniques, i.e. to
determine clades, number of branches on evolutionary "tree")
4. Broad knowledge of primates and mammals (from biophysics to socioecology, to
interpret functional anatomy and behaviour)
5. Knowledge of other sciences (biochem, molecular biology, genetics,
sedimentology, geophysics, zoology, ecology, etc...)
Taphonomy: the study of the process of sedimentation and formation of a site, and whether
materials are in primary or secondary context. Includes the process that occurs with an
organism after its death.
Context: the environmental setting where an archaeological trace is found.
Primary context: the setting in which the archaeological trace was originally
deposited.
Secondary context: one in which the specimen has been moved (such as by the
action of a stream).
Taphonomic processes and diagenesis: must consider soil pH / drainage, water, geology,
weathering (sun, wind), roots, animal and insect activity (bioturbation), subsequent human
activity, looting
Dating methods: placing sites and fossils into a time frame
Relative dating: whether an object is older or younger than other objects
stratigraphy
the law of superposition states that a lower stratum (layer) is older
than a higher stratum
drawback: disturbances shift strata and objects, making it difficult to
reconstruct history
biostratigraphy (aka faunal correlation)
comparing faunal remains to those from other sites with known
dates
dates when fossil pigs, elephants, antelopes were present can be
used to cross check the other dating methods
flourine analysis
applied to bones to assess the amount of flourine in ground water
incorporated during fossilization (the longer the time, the more
flourine incorporated)
drawback: only useful with bones found at the same location
Chronometric (absolute) dating: age in years
Potassium / argon
involves the decay of potassium into argon gas
K/Ar has a half-life of 1.25 billion years
best samples include rocks heated at extremely high heat, e.g. by
volcanic activites
Carbon-14
decay of radioactive isotope 12C and 14C; half-life of 5730 years
used to date organic materials, e.g. cloth, wood, bone
limit: <1000 years old - 75000 years
Thermoluminescence
relies on the principle of radiometric decay
stone contains trace amounts of radioactive elements (uranium or
thorium)
heating releases displaced beta particles that glow
by heating the sample and measuring its amount of glow, a date can
be determined
Paleomagnetism
geologists carefully take a sample of sediment containing
magnetically charged particles for paleomagnetic dating
they must very precisely record the exact compass orientation so that
it can be correlated with the sequence of magnetic orientations
"Molecular clock" dating
measured by genetic mutations, which occur at a regular rate
infer time since last common ancestor, primate divergences, cladistic
relationships
Overview of the Fossil Primates (Chapter 9)
key questions:
1. what were the oldest primates like, and how do they compare with the most oldest
living primates (lemurs and lorises)?
2. who are the oldest members of Hominoidea, and how do they compare with their
modern counterparts?
Derived traits
key to recognizing human beginnings
examples include orthograde body position (upright) and forward-facing eyes
During the Late Mesozoic, primates were one of many groups of small mammals, from
which diverged:
Euarchonta, the superorder designated for the sister (closely related) orders of tree
shrews, flying lemurs, and primates
origins of primates maybe 80-90 MYA?
the Last Common Ancestor
refers to a hypothetical species that was the last to exist beore speciating into myriad
sister orders
all of the taxa that come after the major speciation are referred to as the
crown group
stem groups are the taxa in a clade before a major speciation event
based on molecular and morphological evidence, the origin of primates (the
divergence time for the LCA) was sometime between 90 and 65 MYA
During the Cenozoic, most primate evolution unfolded. The time period is divided into
seven epochs:
1. Paleocene (65 mya; primate-like mammals, Plesiadapiformes)
2. Eocene (55.8 mya; first true primates, Promisians)
3. Oligocene (33 mya; early Catarrhines, precursors to
4. Miocene (23 mya; monkeys and apes emerge, first humanlike creatures appear)
5. Pliocene (5.3 mya; early humans diversify)
6. Pleistocene (1.8 mya; early Homo develops)
7. Holocene (0.01 mya; the present epoch)
Archaic primates
a major radiation of archaic primates, Plesiadapiforms, occurred 65-52 mya
three main species:
Purgatorius (see text for image)
Plesiadapidae
chipmunk-marmot sized mammals
incisors that were not continuously growing and did not self-
sharpen like those of rodents
Carpolestes
Altiatlasus - classification unsure
Eocene Eurpimates Emerge (55.8 mya)
five distinctive traits:
forward-facing eyes
greater encephalization
postorbital bar
nails, not claws, opposable big toe
features suggest adaptation to a warmer climate w/ year-round rainfall and lush,
broad-leaved evergreen forests
continental isolation
North America and Asia were connected and shared species; Africa,
Antarctica, Australia, and South America remained isolated by water
this was a time of rapid diversification for all mammals