PLACENTAL MAMMALS CLASSIFICATION

• Order PrimatesOrder Primates:– 200 species:

• Prosimians: lemurs, tarsiers, and lorises• Anthropoids: monkeys, apes, and humans

– Most are omnivores omnivores with teeth specialized for a varied diet

– Most tend to live in social groups

PRIMATE

PRIMATE

Biogeography of Mammals

• The history of Earth's geography has helped shape today's mammals

• During the Paleozoic Era, the continents were one large landmass, and mammals could migrate freely across it

• But as the continents drifted farther and farther apart during the Mesozoic and early Cenozoic Eras, ancestors of mammal groups were isolated from one another

• Each landmassEach landmass took with it a unique array of mammal groups

Biogeography of Mammals

• Similar ecological opportunities on the different continents have produced some striking examples of convergent evolution in mammals– Thousands of kilometers apart, mammals evolved

similar adaptations in form and function

• When some of the landmasses merged in the late Cenozoic Era, mammals dispersed and intermingled in new habitats

• Living mammals reflect the diversity that resulted from these events.

Convergent Evolution

• Similar ecological opportunities on different continents have resulted in convergent evolution among these and other mammals

• Mammals that feed on ants and termites evolved not once but five times in different regions

• Powerful front claws; a long, hairless snout; and a tongue covered with sticky salvia are common adaptations in these insect-eating animals

Convergent Evolution

CONVERGENT EVOLUTION

 Primates and Human Origins

• Our own species, Homo sapiens, belongs to the order that also includes lemurs, monkeys, and apes

• Carolus Linnaeus named our order Primates, which means “first” in Latin“first” in Latin

What Is a Primate?

• Just what are primates “first” in?

• When the first primates appeared, there was little to distinguish them from other mammals besides an increased ability to use their eyes and front limbs together to perform certain tasks

• As primates evolved, however, several other characteristics became distinctive

What Is a Primate?

• Primates share several important adaptations, many of which are extremely useful for a life spent mainly in trees

• In general, primates have:– Binocular visionBinocular vision– Well-developed cerebrumWell-developed cerebrum– Relatively long fingers and toesRelatively long fingers and toes– Arms that can rotate around their shoulder jointsArms that can rotate around their shoulder joints

HUMAN EVOLUTION• Paleoanthropologists: scientists who study human evolution• Classification of Humans:

– Class: MammaliaClass: Mammalia– Order: Primates (erect mammal)Order: Primates (erect mammal)

• Opposable thumb: ability to grasp• Flattened nails rather than claws• Forward facing eyes: stereoscopic vision• Color vision (cones in retina)• Periodic vertical positioning (upright erect posture)• Shrews, Tarsiers, Lemurs, Monkeys, Apes (gibbons, chimpanzees,

orangutans, gorillas), humans – Subgroup: Anthropoids (monkeys, apes, humans)

» Welled developed collarbone, rotating shoulder joints, and partially rotating elbow joints gives skeletal strength and flexibility

» Opposable thumb» Larger brain (cerebrum) (increase cranial capacity)

TARSIER

GIBBON

CHIMPANZEE

GORILLA

HUMAN EVOLUTION• Human Characteristics:

– BipedalismsBipedalisms: upright walking on two legs (unique human trait)– Broader PelvisBroader Pelvis allowing for bipedal posture and supporting internal

organs– Foramen MagnumForamen Magnum: opening in the skull where the spinal cord enters is

at the very bottom of the skull• Allows the vertebral column to support the head during bipedal walking• Sockets of pelvis positioned so that the leg bones extend vertically

downward• Central opening larger in female

– Larger cranial capacityLarger cranial capacity (1400 cc)– Vertical foreheadVertical forehead– Opposable thumbOpposable thumb capable of moving farther across the hand– Big toeBig toe aligned with other toes helping distribute body weight during

upright walking– V-shaped jawV-shaped jaw (round shape)– No spacing between smaller teeth (omnivores)No spacing between smaller teeth (omnivores)

Fingers, Toes, and Shoulders 

• Primates normally have five flexible fingers that can curl around objects

• Most also have flexible toes• Flexible digits (fingers and toes) enable many primates

to run along tree limbs and swing from branch to branch with ease

• Primates' arms are well adapted to climbing because they can rotate in broad circles around a strong shoulder joint

• In most primates, the thumb and big toe can move against the other digits– The presence of this adaptation allows many primates to hold

objects firmly in their hands or feet

HUMAN EVOLUTION

HUMAN EVOLUTION

Well-Developed Cerebrum 

• The large and intricate cerebrum of primates—including a well-developed cerebral cortex—enables them to display more complex behaviors than many other mammals

• For example, many primate species have elaborate social behaviors that include adoption of orphans and even warfare between rival primate troops

HUMAN EVOLUTION

Binocular Vision 

• Many primates have a flat face, so both eyes face forward with overlapping fields of view– This facial structure gives primates excellent

binocular vision

• Binocular visionBinocular vision is the ability to merge visual images from both eyes, thereby providing depth perception and a three-dimensional view of the world

• This is a handy adaptation for judging the locations of tree branches, from which many primates swing

TARSIER

Evolution of Primates• Humans and other primates evolved from a common ancestor that lived

more than 65 million years ago• Early in their history, primates split into several groups• Primates that evolved from two of the earliest branches look very little

like typical monkeys and are called prosimians• Members of the more familiar primate group that includes monkeys,

apes, and humans are called anthropoids

Primate Evolution

• This diagram illustrates the phylogeny of modern primates

• The two main groups of primates are prosimians and anthropoids

Primate Evolution

Prosimians

• With few exceptions, prosimians alive today are small, nocturnal primates with large eyes that are adapted to seeing in the dark– Many have doglike snouts

• Living prosimians include the bush babies of Africa, the lemurs of Madagascar, and the lorises and tarsiers of Asia

Anthropoids  • Humans, apes, and most monkeys belong to a group called

anthropoids, which means humanlike primates• This group split very early in its evolutionary history into two

major branches: These branches became separated from each other as drifting continents moved apart– One branch, found today in Central and South America, is called

the New World monkeys• After Columbus's voyage to America, Europeans began to use the term New

World to refer to North and South America• New World monkeys, which include squirrel monkeys and spider monkeys,

live almost entirely in trees• These monkeys have long, flexible arms that enable them to swing from

branch to branch• New World monkeys also have a long, prehensile tailNew World monkeys also have a long, prehensile tail

– A prehensile tail is a tail that can coil tightly enough around a branch to A prehensile tail is a tail that can coil tightly enough around a branch to serve as a “fifth hand” serve as a “fifth hand”

Anthropoids 

• The other anthropoid group, which evolved in Africa and Asia, includes the Old World monkeys and great apes– Old World monkeys, such as langurs and macaques, spend

time in trees but lack prehensile tails

• Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans

• Recent molecular studies confirm that chimpanzees Recent molecular studies confirm that chimpanzees are humans' closest relatives among the great apesare humans' closest relatives among the great apes– Humans and chimps share an astonishing 98 percent of Humans and chimps share an astonishing 98 percent of

their DNA!their DNA!

Hominid Evolution

• Between 6 and 7 million years ago, the hominoid line gave rise to a branch that ultimately led to the ancestors and closest relatives of modern humans

• The hominid family, which includes modern humans, displayed several distinct evolutionary trends

• Fossil evidence shows that as hominids evolved over millions of years, they became able to walk upright and developed thumbs adapted for grasping

• They also developed large brains

Hominid Evolution• The skull, neck, spinal column,

hipbones, and leg bones of early hominid species changed shape in ways that enabled later species to walk upright

• The figure at right shows some ways in which the skeletons of modern humans differ from those of gorillas

• The evolution of this bipedal, or two-foot, locomotion was very two-foot, locomotion was very important, because it freed both important, because it freed both hands to use toolshands to use tools

• Meanwhile, the hominid hand Meanwhile, the hominid hand evolved an opposable thumb evolved an opposable thumb that enabled grasping objects that enabled grasping objects and using toolsand using tools

Hominid Evolution• Hominids also displayed a

remarkable increase in brain size

• Chimpanzees, our closest living relatives among the apes, have a brain size of 280 to 450 cubic centimeters

• The brain of Homo sapiens, on the other hand, ranges in size from 1200 to 1600 cubic centimeters!

• Most of the difference in brain Most of the difference in brain size results from an enormously size results from an enormously expanded cerebrum—the expanded cerebrum—the “thinking” area of the brain“thinking” area of the brain

Human and Gorilla Skeletons

• Modern hominids walk upright on two legs; gorillas use all four limbs

• According to the chart and illustration, what are the other differences between humans and gorillas?

Human and Gorilla Skeletons

Early Hominids 

• Paleontologists have unearthed a treasure trove of hominid species

• At present, most paleontologists agree that the hominid fossil record includes at least these genera—Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo—and as many as 20 separate species

• This diverse group of hominid fossils covers roughly 6 million years

• All these species are relatives of modern humans, but not all of them are human ancestors

– To understand that distinction, think of your family

• Your relatives may include aunts, uncles, cousins, parents, grandparents, and great-grandparents

• Of these, only your parents, grandparents, and great-grandparents are your ancestors

HOMINID EVOLUTION

• Hominids: subgroup of primates that includes human beings (Homo sapiens) and their immediate ancestors– Fossil record indicates a trend toward:

• BipedalismBipedalism• Increased cranial capacityIncreased cranial capacity• Evolution of cultureEvolution of culture:

– indicative of behavior that is dependent on learning and on passing knowledge from one generation to the next

– Culture is all the information and ways of living built up by a group of human beings

» Passed from one generation to the next

Early Hominids 

• Almost a third of all known hominid species have been discovered in the last 20 years

• This shows how rapidly knowledge of hominid fossils is growing

• It also explains why hominid evolution is both fascinating and confusing

• What once looked like a simple “human family tree” now looks more like a dense, branching shrub

• Many questions remain about how fossil hominids are related to one another and to humans

• Let's examine a few of the most important discoveries

Human-Fossil Seekers

HOMINID EVOLUTION

• Australopithecus:– Earliest genus of hominids– Means “southern ape”– First found in South Africa– No evidence of tools– Four species:

• Australopithecus afarensis• Australopithecus africanus• Australopithecus robustus• Australopithecus boisei

AUSTRALOPITHECUS

Australopithecus

• One early group of hominids, members of the genus Australopithecus, lived from about 4 million to a million years ago

• These hominids were bipedal apes that spent at least some time in trees

• The structure of their teeth suggests a diet rich in fruit

• Some Australopithecus species seem to have been human ancestors, while others formed separate branches off the main hominid line

Australopithecus

• The best known species is Australopithecus afarensis—described from a remarkably complete female skeleton, nicknamed Lucy, who stood only about 1 meter tall

• The humanlike footprints, which are between 3.8 and 3.6 million years old, were probably made by members of the same species as Lucy

• Since Australopithecus fossils have small brains, the Laetoli footprints show that hominids walked bipedally long before large brains evolved

Australopithecus Footprints 

• Between 3.8 and 3.6 million years ago, members of a species of Australopithecus made these footprints at Laetoli in Tanzania

• The footprints show that hominids walked upright millions of years ago

Australopithecus Footprints 

AUSTRALOPITHECUS

HOMINID EVOLUTION

• Australopithecus afarensis:– Oldest fossil dated between 3 million and

3.5 millions years old (Lucy)– Shorter than modern humans

(approximately 1.5m or 5 ft tall)– Bone structures indicate bipedalism – Cranial capacity between 380 and 450 cc

(1/3 modern humans)

HOMINID EVOLUTION

• Australopithecus africanus:– Lived 2.2 million to 3 million years ago– Slightly taller and heavier than A. afarensis– Cranial capacity slightly larger than A.

afarensis: between 430 and 550 cc

HOMINID EVOLUTION

• Australopithecus robustus:– Southern Africa

• Australopithecus boisei:– Eastern Africa

• Both species:– Lived between 1 million and 2 million years ago– Heavier skulls than A. africanus– Larger back teeth than A. africanus– Larger cranial capacity than A. africanus: between

450 and 600 cc

Paranthropus

• Three later species, which grew to the size of well-fed football linebackers, were originally placed in the were originally placed in the genus Australopithecusgenus Australopithecus– However, they are now usually placed in their own However, they are now usually placed in their own

genus, genus, ParanthropusParanthropus• The known Paranthropus species had huge, grinding

back teeth• Their diets probably included coarse and fibrous

plant foods like those eaten by modern gorillas• Most paleontologists now place Most paleontologists now place ParanthropusParanthropus on a on a

separate, dead-end branch of our family treeseparate, dead-end branch of our family tree

Recent Hominid Discoveries  • Early in 2001, a team led by

paleontologist Meave Leakey announced that they had uncovered a skull in Kenya

• Its ear structures resembled those of chimpanzees, and its brain was rather small

• Yet some of its facial features resembled those of fossils usually placed in the genus Homo

• Paleontologists put this skull in a new genus, Kenyanthropus. Kenyanthropus is shown in the middle in the figure at right

• Evidence indicates that this species existed at the same time as A. afarensis

Recent Hominid Discoveries 

• Then, during the summer of 2002, paleontologists working in the desert in north-central Africa announced the discovery of an even more startling skull

• This fossil skull, tentatively called Sahelanthropus, is nearly 7 million years old

• If scientists agree that Sahelanthropus is indeed a hominid, it would be a million years older than any hominid previously known

Recent Hominid Discoveries  • Sahelanthropus had a brain

about the size of a modern chimp, yet its short, flat face is more like that of a human

• In fact, this skull seems more humanlike in certain ways than Lucy (A. afarensis), who lived several million years later

• While most hominid fossils have been discovered in eastern Africa, Sahelanthropus was discovered much farther to the west

• This suggests that there may be This suggests that there may be many more fossil hominids to many more fossil hominids to be found in widely separated be found in widely separated parts of Africa parts of Africa

HOMINID EVOLUTION

• Homo habilis:– Means “handy human”– Cranial capacity between 600 to 800 cc– Made and used stone tools– Found in southern and eastern Africa– Lived between 1.6 and 2 million years ago– Region of brain essential to speech was

developed in this species– Tool marks on animal bones indicated that they

ate meat– No taller than Australopithecines

HOMINID EVOLUTION

• Homo erectus:– Means “upright human”– Found in many parts of the world (first found on the Pacific

island of Java)– Lived between 0.5 million and 1.6 million years ago– Compared to modern humans:

• Skull is thickerSkull is thicker• Large brow ridgesLarge brow ridges• Low foreheadLow forehead• Very small chinVery small chin

– Cranial capacity between 700 and 1,250 cc– Tall as modern man– Used fire for cooking and warmth– Used modified finely crafted stone tools– Lived in groups

HOMO ERECTUS

HOMO ERECTUS

Hominid Skulls

• Paleontologists’ interpretations of hominid evolution are based on he study of fossils such as these skulls—Sahelanthropus tchadensis (left), Kenyanthropus platyops (middle), and Homo erectus (right)

• Sahelanthropus may be the Sahelanthropus may be the earliest known hominidearliest known hominid

• Which of these skulls most closely resembles the skull of a modern human?

Hominid Skulls

Rethinking Early Hominid Evolution 

• Together with other recent fossil finds, the discovery of Kenyanthropus and Sahelanthropus have dramatically changed the way paleontologists think about hominid evolution

• Researchers once thought that human evolution took place in relatively simple steps in which hominid species, over time, became gradually more humanlike

• It is now clear that hominid evolution did not proceed by the It is now clear that hominid evolution did not proceed by the simple, straight-line transformation of one species into anothersimple, straight-line transformation of one species into another

• Rather, like the evolution of other mammalian groups, a series Rather, like the evolution of other mammalian groups, a series of complex adaptive radiations produced a large number of of complex adaptive radiations produced a large number of species whose relationships are difficult to determinespecies whose relationships are difficult to determine

• Which hominids are true human ancestors?• Which are just relatives?• And how are all those species related to one another and to

modern humans?• At present, no one can answer these questions At present, no one can answer these questions

Rethinking Early Hominid Evolution 

• So what is known about hominid evolution?

• As shown in the figure at right, the hominid fossil record now dates back nearly 7 million years, close to the time that DNA studies suggest for the split between hominids and the ancestors of modern chimpanzees

• In addition, there are many known fossil hominid species, several of which display a confusing mix of primitive and modern traits

• It will probably take many years of work to more fully understand this fascinating and complex story

Hominid Evolution • The diagram shows fossil hominids

and the time ranges during which they may have existed

• The time ranges are likely to change as paleontologists gather new data

• The question mark after Sahelanthropus tchadensis indicates that scientists are not yet certain that this species is a hominid

• Paleontologists do not yet have enough information to know how hominid species are related

• It is now clear that hominid evolution did not proceed by the simple, straight-line transformation of one species into another

• Current hypotheses about early Current hypotheses about early stages of human evolution stages of human evolution recognize the incompleteness of the recognize the incompleteness of the datadata

Hominid Evolution

HOMINID EVOLUTION

• Homo sapiens: “thinking human”– Neanderthals:

• Fossils from 35,000 and 130,000 years ago found in Europe, Asia, and Africa

• Early Homo sapiens• Heavy bone• Thick brow ridges• Small chin• Cranial capacity: 1,450 cc (slightly larger than cranial capacity of

modern humans)• 1.5m or 5ft tall• Stocky• Adapted to cold weather• Lived in caves and stone shelters• Carefully shaped stone tools

HOMINID EVOLUTION

• Homo sapiens: “thinking human”– Cro-MagnonsCro-Magnons:

• Fossils found in Europe, Africa, Asia, and Australia• Cranial capacity approximately 1,400 cc• High forehead• Prominent chin• Lack brow ridges• Taller than Neanderthals: 1.6 m or 6 ft• Sophisticated culture• Made a variety of tools: blades, harpoons, scrapers, drills,

fishhooks, needles• Decorated walls of caves with paintings of animals they

hunted• Regarded as modern humans

HOMO SAPIEN

HOMO SAPIEN

HOMO SAPIEN

The Road to Modern Humans

• The hominids that have been mentioned so far, such as Paranthropus and Australopithecus, all lived millions of years before modern humans

• When did our species, Homo sapiens, appear?• Other species in our genus existed before H.

sapiens, and at least two other species in the genus Homo existed at the same time as early humans

• As is the case with earlier hominid fossils, As is the case with earlier hominid fossils, paleontologists still do not completely paleontologists still do not completely understand the history and relationships of understand the history and relationships of species within our own genusspecies within our own genus

Hominid Evolution • The diagram shows fossil hominids

and the time ranges during which they may have existed

• The time ranges are likely to change as paleontologists gather new data

• The question mark after Sahelanthropus tchadensis indicates that scientists are not yet certain that this species is a hominid

• Paleontologists do not yet have enough information to know how hominid species are related

• It is now clear that hominid evolution did not proceed by the simple, straight-line transformation of one species into another

• Current hypotheses about early stages of human evolution recognize the incompleteness of the data

HOMINID EVOLUTION

• Theories of Hominid Evolution– Two different views still being debated

HOMINID EVOLUTION

Hominid Evolution

The Genus Homo 

• About 2.5 million years ago, a new kind of hominid appeared

• Its fossils show that it resembled modern humans enough to be classified in the genus Homo

• Because these fossils were found with tools made of stone and bone, researchers called the species Homohabilis, which means “handy man”

The Genus Homo 

• Homo habilis was the first of several species in our genus to arise in Africa

• About 2 million years ago, a species larger than H. habilis appeared

• It had a bigger brain and downward-facing nostrils that resembled those of modern humans– Today, most researchers call the African fossils of this

species Homo ergaster• At some point, one or more species in the genus

Homo began migrating out of Africa through what is now the Middle East– That species may have been That species may have been H. ergasterH. ergaster or a closely related or a closely related

species named species named Homo erectusHomo erectus

Out of Africa—But Who and When?

• Researchers agree that our genus originated in AfricaResearchers agree that our genus originated in Africa• But many questions remain• When did hominids first leave Africa?• Did more than one species make the trip?• Which of those species were human ancestors and which were merely relatives?• Fossil data and molecular evidence suggest that hominids left Africa in several

waves as shown in the figure• By a million years ago, migrants from Africa had crossed Asia and reached China By a million years ago, migrants from Africa had crossed Asia and reached China

and Java, and populations of and Java, and populations of H. erectusH. erectus were living in several places across Asia were living in several places across Asia

Out of Africa—But Who and When?

• Many researchers have hypothesized that H. erectus was the first of our genus to leave Africa

• Two recently discovered fossil skulls may offer additional evidence that H. erectus did leave Africa and migrate long distances

• The skulls, which strongly resemble African H. erectus fossils and are about 1.75 million years old, were discovered in the country of Georgia, which is north of Turkey and far from Africa

Out of Africa—But Who and When?

• However, other evidence makes the situation less clear• Another 1.75-million-year-old skull found in Georgia resembles 1.9

million-year-old Homo habilis skulls from Kenya• Does this skull indicate that H. habilis left Africa before H.

erectus?• The scientific jury is still evaluating the evidence

Out of Africa—But Who and When?

• Paleontologists are also unsure exactly where and when Homo sapiens arose

• One hypothesis, the multi-One hypothesis, the multi-regional modelregional model, suggests that modern humans evolved independently in several parts of the world from widely separated populations of H. erectus

• Another hypothesis, the out-of-Another hypothesis, the out-of-Africa modelAfrica model, proposes that modern humans evolved in Africa between 200,000 and 150,000 years ago, migrated out to colonize the world, and replaced the descendants of earlier hominid species

• Scientific debate, and the search for more data, continue

Hominid Migration• Data show that relatives and ancestors of modern humans left

Africa several different times• But when did early hominids leave Africa, and how far did they

travel?• By comparing the mitochondrial DNA of human populations By comparing the mitochondrial DNA of human populations

around the world, and by continuing to study the fossil record, around the world, and by continuing to study the fossil record, scientists hope to improve our understanding of the complex scientists hope to improve our understanding of the complex history of Homo sapienshistory of Homo sapiens

Hominid Migration

Modern Homo sapiens

• The story of modern humans over the past 500,000 years involves two main groups– The earliest of these species is now called Homo

neanderthalensis, named after the Neander Valley in Germany where their remains were first found

• NeanderthalsNeanderthals, as they are commonly called, flourished from Europe through western Asia between about 200,000 and 30,000 years ago

• Evidence from Neanderthal sites in Europe and the Middle East suggests that they not only made stone tools but also lived in organized social groups

Modern Homo sapiens

• The other group is anatomically modern Homo sapiens—in other words, people whose skeletons look like those of modern humans– These H. sapiens, who probably arose in Africa, appeared in

the Middle East around 100,000 years ago• They joined Neanderthals who had been living in

that region for at least 100,000 years• As far as anyone can tell, Neanderthals and Homo As far as anyone can tell, Neanderthals and Homo

sapiens lived side by side in what is now Israel, sapiens lived side by side in what is now Israel, Lebanon, Syria, and Turkey for around 50,000 years, Lebanon, Syria, and Turkey for around 50,000 years, using similar tools and living in remarkably similar using similar tools and living in remarkably similar waysways

Modern Homo sapiens

• That situation may have changed dramatically around 50,000–40,000 years ago

• According to one hypothesis, that's when some populations of H. sapiens seem to have fundamentally changed their way of life

• They used new technology to make more sophisticated stone blades, and made elaborately worked tools from bones and antlers

• They produced spectacular cave paintings• These Homo sapiens buried their dead with elaborate rituals• In other words, these people began to behave like modern In other words, these people began to behave like modern

humanshumans• About 40,000 years ago, one such group, known as Cro-About 40,000 years ago, one such group, known as Cro-

Magnons, appeared in EuropeMagnons, appeared in Europe

Modern Homo sapiens

• By 30,000 years ago, Neanderthals had disappeared from Europe—and from the Middle East as well

• How and why they disappeared is not How and why they disappeared is not yet knownyet known

• But since that time, our species has But since that time, our species has been Earth's only hominidbeen Earth's only hominid