Earth History, Ch. 19 1faculty.chas.uni.edu/~groves/EHCh19lecturept1.pdfEarth History, Ch. 19 15 Earliest hominids • Sahelanthropus is an intermediate between early apes and first

Earth History, Ch. 19 1

Ch. 19—The Neogene World

• Neogene Period

includes Miocene,

Pliocene and

Pleistocene epochs

• Beginning of

Holocene was

approx. 12,000

years ago

Cen

ozo

icPaleogene

Neogene

Paleocene

Eocene

Oligocene

Miocene

Pliocene

Pleistocene

65

24

5.3

1.812,000 years

Holocene


Today’s outline

• Glaciation

• Human evolution


Continental glaciation

• Early Neogene climate was relatively mild

• In mid-Pliocene time, ~3.2 million years

ago, modern ice age began

• Ice age continues today, although glacial

maxima and minima are cyclical, and we

are now in an “interglacial” episode


Northern

Hemisphere

continental

glaciers


Continental glaciation• Bering Land Bridge was ice-free and a corridor for faunal

interchange between North America and Asia


Waxing and waning of glaciers

• High frequency glacial and interglacial cycles:

– Periodic changes in the tilt of Earth’s axis relative to

plane of orbit

– Periodic changes in the orbit itself, due to gravitational

pull of other planets

• Cycles can be documented through oxygen

isotope records

• Waxing and waning has displaced plant

ecosystems by up to 20° latitude


Oxygen

isotope

record

(these should be

positive numbers)


Displacement of floral

ecosystems


Origin of the Great Lakes and

Lake Bonneville

• Retreat of glaciers after the most recent

glacial interval left behind large basins that

eventually filled with water

– Great Lakes formed within the past 10,000 to

15,000 years

– Lake Bonneville covered much of Utah; now

the Great Salt Lake is a “tiny” remnant


Great Lakes and Lake Bonneville


What was the ultimate cause of

Pliocene-Pleistocene glaciation?

• Probably related to creation of Isthmus of

Panama

– Modification of global ocean currents

– Separation of Atlantic and Pacific oceans

resulted in dramatic cooling of Arctic Ocean

water



Human Evolution:

Superfamily Hominoidea

includes gibbons, man,

and apes.

Homo is the only genus

in Family Hominidae;

sapiens is the only species

in the genus Homo.


Early origins

• Earliest “hominoid” fossils are from Africa, ~20 Ma (early Miocene)

• These early “hominoids” are probably ancestral to both modern hominids and pongiids, but fossil record is spotty

• mid- to late-Miocene was a time of “hominoid”radiation throughout Africa and Eurasia (more “apes” then than now!)


Earliest hominids

• Sahelanthropus is an intermediate between early apes and first true hominids

– Known from Chad in beds 6-7 Ma

• Earliest true hominids appeared at ~5.3 Ma, the australopithecines

– Australopithecus, Paranthropus

• Australopithecus (4.0-2.3 Ma) was intermediate in appearance between modern apes and humans (not an evolutionary intermediate):

– Males larger than females (4.5 ft vs. 3.5 ft)

– Brain size barely larger than modern chimp

– Bi-pedal, but spent much time in trees


Sahelanthropus tchadensis

Discovered in 2002 by

Dr. Michel Brunet


Australopithecus

“Lucy”, a female of the

species A. afarensis,

found in 3.2 Ma beds

In Ethiopia


Bi-pedal

Australopithecus

tracks preserved

in volcanic ash,

~3.0 Ma, from

Tanzania


Early Homo

• Australopithecus branched into at least two

species (A. afarensis and A. africanus)

• earliest Homo originated from

Australopithecus approximately 2.4 Ma

• By 2.0 Ma, at least two species of early

Homo were in existence


Hominid

stratigraphy


Early Homo

• Characteristics of early Homo:

– Large brain (800 cm3 vs only 450 cm3 for

Australopithecus)

– Smaller teeth

– Ability to make and use stone tools

• Meat in diet

– Spent most of the time on the ground (not in

trees)


Hominid brain capacity


skull of Homo habilis

2.5 Ma stone tools


Brain size vs. mode of life

• Brain of all newborn primiates = ~10% of body weight

– Brain growth stops shortly after birth in monkeys and apes

– Brain growth continues for ~1 year in Homo

• Homo development is delayed relative to chimps and apes

• Delayed maturation of Homo requires significant parental care

– Parents must hold babies, thus arms not free to hold onto tree branches



Brain size vs. mode of life

• Development of large brain may be related

to climatic change in Africa (~2.5 Ma):

– Drying out of climate reduced forests

– Life on ground may have paved the way for

prolonged parental care

– Bipedalism probably preceeded increase in

brain size


Homo erectus

• Homo erectus evolved from early Homo

approximately 1.6 Ma

• First hominid to migrate beyond Africa

– “Peking Man”, “Java Man”

• Looked similar to modern humans, but:

– Slightly smaller brain (1000 cm3 vs 1400 cm3)

– Narrower pelvis


Homo erectus

Bones of an 11 or 12 year

old boy (1.6 Ma)


Homo neanderthalensis

• Neanderthal fossils are known in Eurasia in beds ranging from 100,000 to 35,000 years old

– Probably originated from a European or Asian population of H. erectus or related species

• Fossils commonly found in cave deposits

– Probably practiced some form of religion

– Buried dead family members with food and tools


Neanderthal

burial


Homo sapiens

• Homo sapiens (modern humans) originated

in Africa ~150,000 ybp (presumably from

an African popolation of H. erectus or

related species)

• DNA from H. sapiens and H.

neanderthalensis indicates that ancestral

populations may have diverged by 500,000

ybp


Homo sapiens

• Homo sapiens seemingly stayed in Africa

for several tens of thousands of years before

migrating to Europe

• Oldest European fossils of H. sapiens are

~33,000 ybp—about the same time H.

neanderthalensis vanished

Documents

Earth History, Ch. 19 1faculty.chas.uni.edu/~groves/EHCh19lecturept1.pdfEarth History, Ch. 19 15 Earliest hominids • Sahelanthropus is an intermediate between early apes and first