Birds (class Aves) are the most diverse of all terrestrial vertebrates-28 orders, 166 families, about 8600 species

Arose about 150 MYA; Archaeopteryx

Birds still retain many reptilian and dinosaur traits-Amniotic eggs and scales on legs; skeletal elements, DNA

Two major traits distinguish them, however from dinosaurs:1. Feathers

-Provide lift for flight and conserve heat2. Flight skeleton

-Bones are thin and hollow -Many are fused (collarbone and keeled breastbone)

3. Physiological adaptations—efficient respiratory system.

Most paleontologists agree that birds are the direct descendants of theropod dinosaurs

Archaeopteryx is the first known bird

-Had skull with teeth

-Feathers on wings and tail

-Forelimbs nearly identical to those of theropods

The most ancient living birds appear to be the flightless birds, such as ostrichs

The largest of the bird orders, Passeriformes, appears to have evolved the latest

Many adaptations enabled birds to cope with the heavy energy demands of flight

1. Efficient respiration-Air passes all the way through lungs in a

single direction2. Efficient circulation

-Muscles receive fully oxygenated blood-Rapid heartbeat

3. Endothermy-Body temperature (40-42oC) permits higher

metabolic rate

There are about 4500 species of mammals (class Mammalia)-Lowest number among 5 vertebrate classes

Mammals differ from other vertebrates in two fundamental traits:1. Hair

-Long, keratin-rich filaments that extend from hair follicles

-Insulation, camouflage, sensory structure2. Mammary glands

-Females possess mammary glands that secrete milk

Other notable features of mammals include:-Endothermy

-Depends on more efficient: -Circulation – Four-chambered heart -Respiration – Diaphragm

-Placenta-Specialized organ that brings fetal and

maternal blood into close contact

The mammalian lineage also gave rise to several adaptations in some groups:

1. Specialized teeth -Different types of

teeth are highly specialized to match particular eating habits

2. Digestion of plants -Herbivorous mammals rely on mutualistic partnerships with bacteria for cellulose

breakdown3. Development of hooves and horns -Hooves are specialized keratin pads

-Horns are bone surrounded by keratin-Antlers are made of bone, not keratin

4. Flying mammals: Bats -Bat wing is a leathery membrane of skin and muscle

stretched over 4 finger bones

-Bats navigate in the dark by echolocation

Fossil record shows that mammals evolved from therapsids about 220 MYA-First mammals were tiny, shrewlike, insect-eating, tree-dwelling creatures

-May have been nocturnalMammals reached their maximum diversitymaximum diversity in the

Tertiary periodTertiary period (65-2 MYA)The last 15 million years saw a decline in the total

number of mammalian species

Prototheria (most primitive)-Lay shelled eggs, oviparous-One living group

-Monotremes Theria

-Viviparous: Young are born alive -Two living groups

-Marsupials and placental mammals

Only three living monotremes:-Duck-billed platypus-Echidna

-Have single opening, cloaca for digestive and reproductive tracts

Egg has chorion and amnion, but no shellEmbryo is nourished by abundant yolk

-After birth, it crawls into marsupial pouch-Latches onto nipple & continues to develop

Examples:-Kangaroo-Opossum

Produce a true placenta that nourishes embryo throughout its development-Forms from both fetal and maternal tissue

Includes most living mammals

Primates are the mammals that gave rise to our own species-They evolved two features that allowed them to succeed in an arboreal environment

1. Grasping fingers and toes-First digit is opposable

2. Binocular vision-Eyes are shifted toward the front of the face

About 40 MYA, the earliest primates split into two groups: prosimians and anthropoids

Prosimians-Most are nocturnal-Only a few survive:

-Lemurs, lorises and tarsiers

Anthropoids are diurnal-Include monkeys, apes and humans

Almost 30 MYA, some anthropoids migrated to South America-Descendants called New World monkeys

-All are arboreal-Grasp objects with long, prehensile tails

Anthropoids that remained in Africa gave rise to two lineages-Old World monkeys

-Ground-dwelling or arboreal-None have prehensile tails

-Hominoids-Apes and humans-Have larger brains than monkeys and lack tails

The taxonomic group “apes” is paraphyletic -Living apes consist of gibbons, orangutans, gorillas and chimpanzees

Hominids consist of humans and their direct ancestors-Common ancestor was more like a chimpanzee than a gorilla

The common ancestor of apes and hominids is thought to have been an arboreal climber-Hominids became bipedal, walking upright-Apes evolved knuckle-walking

Differences related to bipedal locomotion1. Human vertebral column is more curved2. Humans carry much of the body’s weight on the lower limbs3. Spinal cord exits the bottom of the skull.4. Limbs have changed in proportion.

There are two major groups of hominids

-Genus Australopithecus -7 species-Older and smaller-brained

-Genus Homo-3-7 species (depending how you count them)

Bipedalism seems to have evolved as australopithecines left forests for grasslands

Did it follow or precede brain enlargement?-African fossils demonstrate that bipedalism extended back 4 MYA-Substantial brain expansion, on the other hand, did not appear until about 2 MYA

Therefore, upright walking came first-However, why it evolved is still a matter of controversy

The first humans (Genus Homo) evolved from australopithecine ancestors about 2 MYA-Thought to be Australopithecus afarensis

In the 1960s, hominid bones were found near stone tools in Africa-Early human was called Homo habilis

-It closely resembled Australopithecus, but had larger brains

H. Hablis was replaced by Homo erectusHomo erectus was a lot larger than H. habilis

-Had larger brain and more rounded jaw-Able to talk

H. erectus became widespread in Africa-Then migrated to Asia and Europe

H. erectus survived for over a million years-Longer than any other human species

Modern humans first appeared in Africa about 600,000 years ago-Three species are thought to have evolved

-Homo heidelbergensis (oldest)-Homo neanderthalensis-Homo sapiens

Some investigators lump all 3 into H. sapiens

H. heidelbergensis -Coexisted with H. erectus in Africa-Had larger brain & more advanced anatomy

H. neanderthalensis-Appeared in Europe 130,000 years ago-Were short, stocky and powerfully built-Had massive skulls

Neanderthals made diverse tools -Took care of sick and buried dead-First evidence of belief in “life after death”

They abruptly disappeared about 34,000 years ago-Replaced by fossils of H. sapiens called the Cro-Magnons

Out of Africa Hypothesis

Recent DNA analysis indicates that Cro-Magnons and Neanderthals didn’t interbreed-Neanderthals are our cousins, not our ancestors

Cro-Magnons had a complex social organization-Thought to have full language capabilities

H. sapiens is the only surviving hominid

-Best fossils are 90-100,000 years old

Hallmarks of H. sapiens evolution

-Progressive increase in brain size

-Effective making and use of tools

-Refined and extended conceptual thought

-Use of symbolic language

-Extensive cultural experience

Human beings differentiated in their traits as they have spread throughout the world

All humans are capable of mating with one another and producing fertile offspring

Some contemporary anthropologists divide people into as many as 30 “races”-Others only three: Caucasoid, Negroid, and Oriental

Humans have relied on visual cues – primarily skin color – to define races

However, groupings based on overall genetic similarity are different from those based on skin color or other visual features

Different groups of people have interbred during the entire course of history -This constant gene flow prevented the formation of different human subspecies

Only 8% of genetic differences can be accounted for by racial differences-Therefore, human races do not reflect significant patterns of underlying biological differentiation