idiosyncratic variation

sexual variation

geographic variation

age-related variation

idiosyncratic variation: variation between individuals

sexual variation: bones differ between males and females, indicate gender behavioral differences (even in transsexuals)

geographic variation: variation from place to place

age-related variation: changes with age 

how people died & how many people died in past populations 

enamel

dentine

enamel: hard exterior of the tooth

dentine: soft interior of the tooth

herbivores have exposed dentine that gets worn away to expose enamel ridges

enamel is glued to dentine by cementum

teeth begin to grow at the tips/cusps as enamel 

different teeth for different functions

like humans 

their teeth have flat cusps for chewing

ever-growing teeth with exposed dentine that gets worn away to expose enamel ridges 

simple molars found in apes 

gap (diastema) between lower canine and lower third sectorial premolar

lower P3 has elongated sideways enamel to sharpen the upper canine 

found in apes and monkeys, but not humans 

first lower premolar

in C/P3 honing complex, it has elongated enamel for honing the upper canine 

gap between teeth

large canines fit into the gap and can be honed 

deciduous

adult

deciduous: baby teeth

some people have multiple sets

humans' deciduous teeth erupt later to allow breast-feeding  

adult teeth

teeth form (deposit enamel) at a known rate and can be used to predict a baby's age, but the pattern of eruption varies

enamel hypoplasia (disruption in enamel formation) indicates trauma (illness, lack of milk, starvation, etc.)

the reconstruction of behavior/appearance based on teeth relies on the observation that form is related to function

teleological view: function is the reason for form 

fibrous joints in the skull

form in the membrane bone of the top part of the skull

as ossification centers move towards each other, they leave sutures in between

bones grow along sutures, allowing the brain to grow very quickly and in all directions

if some sutures are closed, the brain will keep expanding in the direction of the unclosed sutures, causing an irregular skull shape

chewing

reduced force in humans compared to apes 

field studying what happens to an animal after death

developed by Louis Benford, who collapsed the field of archaeology as it was then

sequence involves the death of an organism; damage aboveground (eaten, trampled, moved by water); burial; damage by plant roots and acid, soil deposited on top compressing the bones; geological effects (fault lines, rivers); eventual fossilization (replacement of minerals with rock); exposure of fossil

Steno

Principle of Superposition 

Steno: clergyman who studied shark anatomy

argued that sharks encased in stone were encased before the stone solidified

Law of Superposition: Steno's theory that rocks closer to the surface are younger than those below

Steno suggested that rock layers were due to local flooding events 

layers of rock/earth

deposited at different times

used in stratigraphy to determine how old the contents of a layer are 

Smith

Principle of Faunal Succession 

William Smith: British canal-builder who found fossils in rock layers

Law of Faunal Succession: fossils occurred in layers of rock (strata) in the order in which they lived 

relative dating technique based on the sequence of the layers of earth

differs by area 

only good for dating organic material less than 50,000 years old (relatively recent)

uses known half-life of carbon (5,730 years)

as soon as an animal or plant dies, the carbon 14 accumulated in its body begins decaying to carbon 12 

the ratio of carbon 14 to carbon 12 can be used to date a fossil 

potassium-argon dating

argon-argon dating 

can't date organic matter, requires volcanic matter

a potassium-rich layer of ash from a volcanic explosion contains lots of potassium that slowly decays into argon, so more argon = older

anything less than a million years old can't be dated this way

argon-argon is a more refined technique for recent eruptions 

recently-developed relative dating technique based on the known times when the Earth's magnetic poles reversed alignment

also uses biostratigraphy to get an idea of what time period the magnetic materials

are from 

the time it takes for half of the radioactive particles to decay

used in absolute dating (such as carbon 14, potassium-argon, and argon-argon dating) 

era

period

epoch 

centers of bone formation that converge and eventually become bone

800 in a developing embryo, 400 by birth: this translates to 206 bones in an adult skeleton