Lecture 8 Flashcards
Encephalized
ratio of brain to body size - higher rates for a given species the more encaphalized it is
obligate bipeds
necessary for the special to be bipedal
Facultative bipedalism
adopting a two legged posture only under particular circumstances as an exception to non habitual non-bipedal forms of locomotion
Orthograde
indicating upright or erect posture, notably with regard to the trunk
primates often do this when feeding or grooming others either on the tree or on the ground
Bipedalism Features
- foreman magnum position so that the head is ontop of the spinal column
- s shape in spinal - gives balance of trunk and head
- size of hip joint - weight transfer from trunk to legs
- short broad pelvis and flaring of illium
angle between tibia and knee and then with the femur above the knee is more inwards - foot: loss of opposable toe and development of strong longtidinal and transverse arches in the mid foot
- rearrangement of gluteus medium and gluteus minibus so they act across the hip joint in contraction to provide stability and balance while walking
Benefits to Bipedalism
surveillance - can see over tall grass and be able to see further
can carry objects or infants
managing environmental heat load because the upright posture exposes much less surface area to solar radiation and breezes are stronger higher up - greater convective cooling
less costly in energy compared to quadrapedalism
Drawbacks to bipedalism
heart has to circulate blood against gravity to a much greater degree
fallen arches in feet, prolapse of intervertebr discs in lower back, hernia and knee problems
child birth - obstetric dilemma - children being born very helpless, cannot provide for themselves, completely dependent upon the mother
narrow pelvis for smaller brain size?
Male provisioning hypothesis
provisioning = giving food
bipedalism had a selective advantage in a more open, expansive habitat in which males could range widely carrying tools, weapons and return with food to home base
then would share resources with monogamously pair bonded females and their offspring
Concealed ovulation
males cannot tell when a women is ovulating like the way other primates can tell so they bring food to guaranty paternity
reduction in birth spacing, correlated with a number of variables and access to food resources, higher energy in animal protein
- population increase
- reduction in sexual dimorphism in bones and teeth
Teeth
canine reduction size in hominins
loss of honing complex (diastema gap in which the canine was sharpened)
reduction in sexual dimorphism of teeth
increase in enamel thickness
occlusal plate
orientation of chewing surfaces of upper and lower dentitions -> canines pass through this
Diastema
space between adjacent teeth in which the canine can fit and be sharpened between lower canine and premolar
Canine honing
sharpening the upper canine through repeated contact with 3rd premolar in the sectorial p3
- reduction and loss of complex could be due to less intrasexual selection within males for females or a correlated response because there were fewer female aggressive encounters
Thick enamel
diet changing to hard foods
helps prevent damage to a tooth by restricting the spread of cracks from deep within the tooth
Endocasts
impressions of the inner surface of the cranium and outer surface of the brain, which may occur naturally as fossils or as moulds in the lab
- shows each lobe impression and fissures, vascular supply of arteries and veins and sutures of cranium
- provide information on size, shape and structure of brain
- showed movement of lunate sulcus to the back of brain and increase size of parietal and temporal lobes - this allowed for a greater amount of language capacity
- humans have a decreased size of visual cortex ,but we have increase tool making, memory, social communication and facial recognition
What is a hominin
- bipedal
- lack honing complex dental configuration,
- use, produce and are dependent on tools
- have complex cognitive functions
- have language
Teeth of a hominin
humans have a more elliptical shape, it is less long
smaller teeth and thinner enamel.
reduction in canines
lack honing complex
Tool use
we use and produce tools at a much higher degree that gives us a certain characteristic
other organisms use tools like chimps, crows, magpies, but we use it to a much greater degree
we are entirely dependent on tools for survival
Cognitive function
size of brain and configuration should be increased
Language
modern day hominoids do not have the capacity to achieve language
- mouth is capable of producing sound in combination with voice box
- understanding of symbols in use of meaning
- brain is capable of telling tongue how to move and shape
- language always changes just like our culture
Bipedalism
Cranium/skull need to be balanced on top of spinal column
braincase needs to enter from the bottom not on the side for balance
Foreman magnum - moves to base of skull
S curve spine - distribute weight and provide flexibility and important for childbirth
more rounded chest cavity - rounded rib cage
- pelvic joint and femoral joint - feet need to be closer together when you walk instead of shoulder distance, so femur need to be angled to pelvis inwards and femoral tibia joint to angle the opposite way so that fee are closer together
- redistribution of musculature (from upper body to lower legs)
- foot: no opposable big toe, forward facing
- arch in mid foot and longitudinal muscle
Darwins Hunting hypothesis
frees up the hands to allow you to carry tools to hunt meat and do all things that humans want to do
he came up with these ideas before humans were discovered in Asia/Africa (his time he thought they were in europe)
- meat eating happened way after humans were bipedal
Patchy Forest Hypothesis
Peter Kodman and Henry mcHenry
much cooler and drier environments, forests started to disappear and became patchier, interspread within large savannahs
- bipedalism evolved to efficiently and quickly get from one forest to another
problem; bipedalism evolved in forested environments
Provisioning Hypothesis
Owen Lovejoy’s
Human offspring take a long time to mature and become dependent, mother needs hands to carry baby because it is entirely confined
bipedalism frees up hands and frees up ability to carry and provision (give food) to offspring
Sahelanthropus tchadensis (Toumai)
Micheal Brunet
found in South America - chad
lived 7mya
base of skill (foreman magnum) - indicates could be bipedalism
lack of honing complex
specimen was severely fragmented - not conclusive
Orrorin tugenensis
Brigette Senut and Martin Pickman
kenya
6mya
Transitional detention from hominoids to hominids, reduction in size of enamel
name means original man of tugenensis
or dawn of tugen
1st example of actual biped - lived in forested environments
ruined the patchy forest hypothesis because it lived before the pliocene
Pliocene
5.3-2.5 mya
Climate: cool and dry
reduction in forested areas
hominins proliferated during this time
Olduvia Gorge
place in africa
a lot of hominin fossils
Ethiopia, kenya, south africa
Aradipithecus ramidus
Tim white found in aramis, ethiopia 4.4mya meaning base root biped, transitional dentition - loss of honing complex, small teeth but lots of enamel cranium and pelvis indicated bipedalism
Ardipitheucs kababba
teeth didn’t quite fit in with the ramidus
basal family ancestor
5.5mya
Australopithecus anamensis
Kanapoi Meave Leakey and Alan Walker 4.2 mya Bipedalism and primitive detention sexually dimorphic species teeth look like a very large male - intersexual competition single male/multi female groups dentition were folivores and omnivores (fruit and meat) gracile
Australopithecus afarensis
Hader- Dylan Johnson Laetoli - Mary Leakey lucy specimen 3.8-3.0 mya Clearly bipedal, has spine, pelvis and femur and tibia marked by sexual dimorphism brain case calvarium Transitional dentition Mary Leakey found volcanic ashbed that had footprints of bipedal adult and bipedal subadult to show that there was no knuckle walking and the taking care of the young gracile
Robust Australopithecines
Australopithecus africanus (3-2.5mya): Taung Child - Raymond Dart 1924 Paranthropus Robustus (2.6-1.2mya): Kroomdrai - Robert Broom 1938 Paranthropus Boisei (2.6-2.0mya): Olduvai gorge: mary leakey 1959
Robust:
larger muscle attachment, larger/flatter faces, large sagittal crests with muscle attachment
very strong
Gracile
small slightly built
lack dentition associated with megadonts
Megadonts
very large molars with very thick enamel
good for chewing the hard diet
absence of honing complex - diastema
elliptical or parabolic shape
End of Pliocene
australopithecus garhi middle awash berhane Asfaw 2.5 mya found stone tools - pushed back tool making in time and into a new species
Australopithecus Diet
detention and musculature resembles modern day gorilla/chimp
a lot of foliage, a lot fo chewing, heavy musculature and dentition
- musculature creates sagittal crest growing in response to chewing
- flat cheeks from chewing
- non specialized diet - could eat leaves, insects, fruits
very large gut - folivores need this to break down cellulose
teeth exhibit wear = horizontal stratifications of leaves being pulled through
ate C3 plants - bushes trees and grasses
some c4 (rare) sorghum, millet, corn, and sugar cane
Predators
terrestrial primates subject to predation - need to be big
- predators of australopithecus was leopards
- leopards were subject to harassment for prey so they would take the australopithecus up to a tree with their incisors dug into their skull and their body in-between their legs
Taung child had injuries in the eyelobe from avain attack (large birds like crowned hawk eagle) from beak and talon
Endocasts of australopithecines
show that there is left and right hemispheres and that they exhibit no asymmetry
- lateral sulcus
- they matured very quickly - quicker than chimps, humans, and modern day hominoids
