Lecture: February 27, 2007

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  australopithecine radiation 4-2 mya
  
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  austs may have been an intermediate stage or an ancestor in human evolution
  
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  wide radiation, diverse adaptations, abundant fossil evidence
  
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  Taung baby found by Raymond Dart in S. Africa, foramen magnum (FM) looks like a biped
  
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  Robert Broom – started excavating Sterkfontein - a limestone cave – formed by water seeping in, causing collapses and creating limestone casts around bones
  

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  leopards would bring the kills to the caves – many of which were australopithecines
  
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  a large amount of early hominid fossils came from there
  

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  Mary & Louis Leakey – digging in Olduvai Gorge and found another australopithecine in 1959
  

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  Laetoli footprints found in 1978
  

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  Lucy found by Don Johanson, important because it was relatively intact skeleton
  
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  Species info –
  

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  Sites, major fossils, discovery
  
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  Age, ecological context
  
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  Anatomy – cranial, dental, postcranial, body size / dimorphism (how different the male and female body sizes are)
  
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  Behavior – diet, locomotion, cognition, etc.
  

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  Species name: genus + trivial name, both italicized (i.e. Homo sapiens)
  
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  Rules of precedence - whoever gets to the species first gets to name the species, and if a species is named but turns out not to be a species then that name can never be used again (nomen nutum)
  
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  Type specimen (holotype) – the one fossil specimen that all new specimens must be compared to (no type specimen for homo sapiens)
  
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  2 types of australopithecines – gracile and robust
  
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  Gracile As
  

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  A. anamensis – 3.9-4.2 mya, E. Africa
  
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  A. afarensis – 3-3.7 mya, E. Africa
  
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  A. africanus – 2-3mya, S. Africa
  
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  A. garhi – 2.5mya, E. Africa
  
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  A. bahrelghazali – 3.5 mya, C. Africa
  

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  Robust As
  

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  A. aethiopicus – 2.6mya, E. Africa
  
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  A. boisei – 1.5-2 mya, E. Africa
  
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  A. robustus – 1.5-2 mya, S. Africa
  
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  K. platyops – 3.5 mya, E. Africa
  

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  Ontogeny (development and formation throughout life) issues –
  

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  Humans develop at a slower rate than other primates
  
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  Takes longer for humans to develop all of teeth
  
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  People used to think that As progressed like humans, but more likely that they developed at stages like chimps
  

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  2 major concerns of primates in the wild – eating and not being eaten
  
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  Energy an animal requires based on
  

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  Basal metabolic rate – how much energy an organism uses while at rest
  
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  Active metabolism - how much energy used when active
  
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  Growth rate
  
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  Reproductive effort
  

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  Primates require the correct amount of water, amino acids (to make protein), fats, carbs, vitamins, and minerals
  
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  Primates must avoid toxins – most plants create secondary compounds that prevent them from being eaten
  
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  All primates have 1 primary protein source and 1 primary carb source
  
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  Each primate depends more on one food type than another – names for them:
  

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  Frugivore – depends on fruit
  
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  Folivore – leaves
  
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  Insectivore – insects
  
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  Gummivore – plant gum
  

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  Insectivores bigger than folivores who are bigger than frugivores
  
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  Fruits can be hard to find in rainforests because of short ripening time, few of one type of tree
  
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  Diurnal – active during the day, nocturnal – at night, cathemeral – both
  
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  Primates probably evolved from a nocturnal ancestor
  
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  Territorial primates defend territory and keep other males out, nonterritorial primates’ home ranges may overlap but encounters may be violent
  
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  Territoriality stems from resource protection and mate defense
  
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  Some primates have calls to alert others about predators, some primates of different species join together and keep watch for different types of predators
  
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  Sociality is common in primates but not common in mammals
  
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  Costs and benefits to socialization – better protection vs. competition for resources and mates
  
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  Still some debate as to primary reason why primates form social groups – protection v. resources
  
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  Scramble competition – when resources are distributed evenly across the landscape (ex. candy on the ground after busting a piñata)
  
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  Contest competition – when resources are limited and can be monopolized profitably (ex. musical chairs)
  
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  Dominance relationship – when a certain type of individual wins almost all the time
  
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  Female philopatry – the incentive to stay with one’s kin
  
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  Domination less important when between-group competition is stronger than within-group competition
  
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  Social organization evolution may be difficult to change
  
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  Inbreeding reduces viability of offspring, so males and females leave natal groups when reaching sexual maturity
  

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  Miocene temperature drop caused primates to have to deal with changing African environment
  
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  Hominins began appearing in fossil record 6mya, walked upright and ate new kinds of food, no longer just tree dwellers
  
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  5 factors distinguishing humans from apes
  
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    Walk bipedally
    
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    Dentition / jaw musculature is different
    
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    Larger brains in relation to body size
    
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    Develop slowly – long juvenile period
    
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    Elaborate and symbolic culture transmitted thru spoken language
    
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  Ardipithecus, Orrorin, and Sahelanthropus discussed (see lecture notes for more details)
  
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    Earliest fossils similar to humans
    

Anatomy of the primate postcranium important

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  force can cause bones to deform and (with enough force) break
  
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  (much of this reading is superfluous and covered in lecture)
  

(1925) “Taung Baby” in South African limestone quarry; ancestor of humans

(1959) “The Nutcracker Man” in Olduvai Gorge, Tanzania; stone tools, pushes back age of humans

(1974) “Laetoli Hominid 4”, Laetoli footprints in volcanic ash in Tanzania

(1978) “Lucy” in Hadar, Ethiopia

(1995) A. anamensis in Lake Turkana and Ethiopia

(1999) A. garhi in Bouri, Ethiopia

(2000) K. platyops “Man from Kenya with flat face”

1. 
   Ingestion – food in front of mouth (often incision)
   
2. 
   Stage I transport – food goes to post-canine region
   

3. 
   Mastication – breakdown of food by (pre)molars (“chewing”)
   

Cusps = pestle; valleys = mortar

Unilateral mastication – chew on one side at a time (balancing side – side you are not chewing on and working side – side on which you are chewing)

Temporo-Mandibular Joint (TMJ) has 2 degrees of freedom:

1) Abduction (opening), Adduction (closing)  vertical motion

jaw closing muscles: temporalis (side of temporal lobe)

jaw opening muscles: most important = diagastric

2) Translation (protrusion and retrusion)  horizontal motion

4. 
   Stage II transport – formation of bolus, then to back of oral cavity
   
5. 
   Swallowing
   

Humans: epiglottis and soft-palate are not in contact; shared space for food and air which means much more likely to choke (only mammal for which this is true)

6. 
   Digestion
   

Stomach churns food and excretes acids to break it down

Small intestine – enzymatic breakdown

Liver secretes enzyme to remove waste and filter food

Pacreas

Long intestine – fermentation (microbes); primary water absorption

Apes: opposite

A. Boisei – teeth 3x larger than humans

Megadontia quotient (tooth size per body mass)

1. 
   Boisei < A. Africanus < A. Afarensis
   

Very low bite force for humans (7.9) v. male chimp (13.1)

v. A. Bosei (22.1)

Stresses, however, are about the same (Boisei spreads stress over large surface area)

- Spatulate incisors

- Incisiform canines

- Big front teeth – stripping pith (major fallback food)

- Molarized premolars; more “square shaped”, bigger; cusps

- Enamel thickness

Humans have slightly larger enamel compared to other A.

Prevents your teeth form wearing down; grinding

More cycles, harder food

-- adaptations for chewing so much (spend most of their day eating) –

- cross-sectional area of muscle tells you how many muscle fibers you have, the more the thicker

cross sectional area of temporalis (in the skull) shows you how thick the chewing muscles are

orientation of temporalis (posterior v anterior)

force on front of teeth – posterior orientation

force on molars – anterior orientation (hominids)

-Mechanical advantage

(3^rd class lever system)

condyle higher increases force

pull zygomatic forward, moves masseter forward, increasing length of in-lever and creates more force

facial retraction and rotation

pull teeth inward to create shorter in-lever

-Wide zygomatic arches

sideways movement of jaw

tougher food generates horizontal motion

Force resistance:

resist generated force in order to not create microcracks

Mandibular strains (wishboning, twisting, bending)

Resist strain by putting mass in the plane of the strain

Facial twisting and bending

Make it more flatter, wider, and taller to resist force

Anterior nasal pillars

Putting it all together:

Chewing with high forces, but similar occlusal stresses

Big, thick teeth

High buttressed faces, mandibles

--- BECAUSE eating tough and hard foods (USOs and seeds)

Gracile (fruit/pith/USOs) v. Robust – tough diets, huge muscles etc. (fiber/tubers/seeds)

--Strippers (Africanus) have more scratches than biters.--

more piths (robust)

Incisors: more wear (gracile)

Less wear (robust)

**CARBON**

Carbon12 = stable, C13 also stable and C14 is radioactive

C3 plants – leaves, fruits, corn (browse)

C4 plants – grasses (graze)

Differences btwn C3 and C4: C4 plants have more C13

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  Primate females always provide extensive care for young; males occasionally (mostly in monogamous bonds)
  
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  Males do not care for offspring when can be using resource to acquire additional mates or when extra care would not necessarily increase offspring fitness
  
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  Females invest heavily in ea. offspring; reproductive success depends on ability to obtain enough resources to provide for herself and offspring
  
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  High-ranking females reproduce more successfully than low-ranking females- fight to gain access to food and other resources
  
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  Tradeoff between number of offspring and quality of care provided
  
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  Shift in nature of care/attention; less as offspring grow
  
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  Male reproductive habits dependent on distribution of females
  
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  Sexual selection leans to adaptations that allow males to compete more effectively for access to females; often stronger than natural selection
  
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    Intrasexual selection (competition among males)
    
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      Favors large body size, canines and weaponry
      
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      In multi-male, multi-female groups where females mate with many males, sexual selection favors higher sperm count **hence Lieberman’s references to the benefits of larger testicle size**
      
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    Intersexual selection (female choice)
    
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      Favors: 1) increased male fitness, 2) good genes providing increased offspring fitness, 3) traits making males more conspicuous to females
      

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  Only a few morphological traits developed to attract females
  
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  Substantial variation in reproductive success of males over the course of their lifetimes
  
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  Infanticide as sexually selected male reproductive strategy; linked to changes in male membership and status, shortens IBI, don’t kill own offspring
  
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    Substantial reproductive benefits
    
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    Female response: enlist aid of other males for protection or attempt to confuse males about paternity
    

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  Spread of woodland and savanna led to evolution of first hominids 6mya
  
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  Differences between humans form other hominids: bipedalism, larger brains, slower development, dental morphology, cultural adaptation (Ie. Language)
  
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  A. ramidus similar to humans and chimps (foramen, locomotion, sm. Canines)
  
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  Orrorin Tugamensis similarity to females
  
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  Australopithecus, Paranthropus and Kenyanthropus lived in Africa between 2-4mya
  
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  A. anamensis – bipedal but more apelike skull
  
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  A. afarensis – E. Africa 3-4mya and is best known of the australopithecines
  
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    Derived features shared with humans but ancestral traits include brain size similar to apes
    
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    Bipedal but not necessarily same efficiency of stride
    
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    Laetoli footprints indicate another bipedal species in E. Africa at same time as A. afarensis
    
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    A lot of time in trees
    
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    Sexually dimorphic in size
    

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  A.africanus found in South Africa 3-2.2 mya
  
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    Matured rapidly like chimps
    
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  A. garhi around 2.5mya in E. Africa
  
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  A. habilis/ rudolfensis
  
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    Larger brain and more humanlike teeth ** probably not on test**
    
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    Assigned to australopithecines because not as similar to homo
    

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  Paranthropus aethiopicus = hominid with teeth and skull specialized for heavy chewing
  
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  Paranthropus robustus = more recent species found in S. Africa, very robust
  
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  Kenyanthropus platyops = E. Africa between 3.5mya and 3.2mya
  
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  Reasons for bipedalism:
  
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    Efficient form of ground locomotion
    
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    Erect posture allows hominids to keep cool
    
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    Leaves hands free
    
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    Harvesting of fruit from small trees
    

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  Increased seasonality in rainfall favors a greater dependence on foods available during dry season; corns, tubers, and meet
  
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  Chimps as effective hunters but rarely scavenge
  
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  Early hominids using tools like chimps did
  
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  Chimps share food but very rarely except for mothers and offspring sharing
  
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  Early hominids lived in multi-male, multi-female groups with little male investment in offspring
  

Last common ancestor, something between chimps and humans, around 6 to 8 million years ago

Chimp-like early hominids – like chimps, with bigger, thicker cheek teeth, might be bipeds

Gracile and robust Australopithecines

How do we stand and locomote bipedally?

How does one shift from quadrupedialism to bipedalism? (What are adaptations for bipedalism?)

What was early hominid bipedalism like? (and how would we figure it out?)

When and how did bipedalism evolve?

Why did it evolve?

Problem – what’s the relationship between form and function (of the bones we find)?

Form affects function is by performance – i.e. if I make my legs longer, I can walk more effectively and use less energy  affected by natural selection and sometimes by habitual activity (i.e. running not making your legs longer, but thicker, yet still more efficient)

typical quadrupeds: run and walk on their toes, fore/hind limbs are about the same length, short digits, narrow chests, immobile shoulders, small tails

Arboreal quadrupeds (monkeys) have special adaptations – tend to run on feet rather than just toes, very long olecranon process, scapulas are more on the side (shoulders more mobile)

We evolved from arboreal, suspensory quadrupeds (apes) – very mobile shoulder and hip joints, usually no tails, much shorter olecranon process, very long arms and fingers, mobile wrists, and stabilized trunks due to shorter lumbar regions