Chapter 7

Charles Dawson found a fossil that he said was the “missing link”

It had a human skull and an ape jaw Called Piltdown Man It was a hoax (human skull fused with an

orangutan jaw) Shows people (wrongly) thought human

ancestors were hybrid ape-men

It is not big brains It is bipedalism We began walking bipedally 7 mya

(million years ago) We got big brains only 2 mya

Please remember:Hominids are ancestors of any apesHominins are ancestors of humans

Historically, scientists believed the identifiable feature of human ancestors was big brains

This was not supported in the fossil record How would we tell bipedalism from a fossil?

Also remember that humans go in the ape classification of Hominoid

Why?

Also remember that humans go in the ape classification of Hominoid

Why? Y-5 molar No tail Shared DNA

1. foramen magnum underneath skull 2. short, wide pelvis 3. long legs 4. no opposable big toe 5. double-curved spine

Honing canine: apes’ canines cut and shred food and are large and dangerous and they have a diastema.

Humans have small, nonhoning canines and no diastema

Apes have powerful chewing muscles and a sagittal crest for extra power. Humans are weak chewers

Why? What invention did human ancestors have that made food processing easier?

It is hypothesized that our ancestors were knuckle-walkers, which allowed for easier upright standing

Climate and environmental changes may have selected for bipedalism

Darwin’s Hunting Hypothesis: because of similarities between humans and apes, he concluded Africa must be our origin. There must have been something to shift us to walking on the ground

Unique human traits:Bipedal vs quadrupedalTiny canines vs large canines Tool use vs no tool use Big brains vs smaller brains

Darwin’s Hunting Hypothesis: Darwin asked what advantages bipedalism had and he concluded it freed the hands for holding weapons

We now know that we walked many millions of years before tools were made, but his hypothesis laid the foundation

Another hypothesis involved the forest becoming fragmented, and hominids walking on two legs in between patches of trees. Used less energyCould see predatorsCould hold things with handsLess of the body in direct sunlight

Owen Lovejoy’s Provisioning Hypothesis: heavy parental investment by mothers led to bipedalism

Males would better provision females if bipedal (free hands to carry more food)

Better infant survival and higher fitness for mother

Small level of sexual dimorphism in fossils supports this (cooperation of male and female pair…not males fighting for one female)

Pros:Can carry things (frees hands)Can see predatorsCan save energy

Cons:We are slow If carrying items, makes us easy targetsBack injuries If injure a foot, very difficult to get around

Pre-Australopithecines Australopithecines Paranthropus

Rift Valley Volcanic rock

What dating technique?

Sahelanthropus tchadensis: earliest ancestor/oldest biped

“Chad Man” 7-6 mya Central Africa (Chad) Small brain (350 cubic cm, cc) Bipedal (foramen magnum) Nonhoning canine Close to the divergence of human line

from ape line

Sahelanthropus tchadensis

Orrorin tugenensis: “Original Man” 6 mya Mostly femurs (thigh bone) Show bipedalism Nonhoning canines

Aridpithecus ramidus: “Great-grandma” “Ardi” 4-6 mya Bipedal All species so far still spent time in the

trees…why? May be direct ancestor to

Australopithecines

Aridpithecus ramidus:

Australopithecines: Hundreds of fossils from at least 7

species Not 100% sure of all the relationships

Australopithecus africanus: Raymond Dart found a small skull in a

cave “Taung Baby” 4-3 mya Thought baby ape at 1st Small teeth, bidpedal foramen magnum Later adult fossils had small canines too *Showed that bipedalism came way

before big brains*

Australopithecus africanus:

Australopithecus afarensis: Kenya and ethiopia 3 mya Best-known and best-represented “Lucy” over 40% of skeleton (but over

80% because skeleton is symmetrical) If Ardi is great-grandma, Lucy is

grandma Foramen magnum, pelvis, legs, and feet

all bipedal Curved fingers (why?) Small brain still (430 cc)

Australopithecus afarensis: Smaller canines Laetoli Prints: fossilized footprints in

volcanic ash (how would you date these??)

Showed bipedalism and ‘first family’ (2 adults, 1 child)

Australopithecus afarensis:

Australopithecus:

Beginning 3mya, two lines of hominin evolution occurred, each with unique adaptations

One line went extinct and one line led to genus Homo

This next group is the second line that went extinct

Some still call this group “robust” Australopithecus but there are enough differences that I split them into a new genus Paranthropus

Paranthropus: 2.5 mya Larger, more robust bodies but small brains Sagittal crest Huge molars for crushing tough food Flaring face Do we have these adaptations? Specialized food source may have led to

extinction

Paranthropus:

AUSTRALOPITHECUS

Biped Slender Small brain Rounder head Smaller teeth Varied diet

PARANTHROPUS

Biped Robust Small brain (smaller

than A.) Flared head Sagittal crest Large molars Specializeed, tough

diet