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Chordates (phylum Chordata) are deuterostome
coelomates
-Nearest relatives are echinoderms (the only other
deuterostomes)
Four features characterize chordates
1. Nerve cord
2. Notochord
3. Pharyngeal slits
4. Postanal tail
Phylum chordata can be divided into three subphyla
1. Urochordata
Nonvertebrates
2. Cephalochordata
3. Vertebrata
Tunicates are marine animals
-Larvae are tadpole-like and have notochord and nerve cord
-Are free-swimming but do not feed
-Adults typically lose the tail and notochord
-Are immobile filter-feeders
-Many secrete a tunic (cellulose sac) that surrounds the animal
Lancelets are scaleless chordates
-Notochord persists throughout animal’s life
-Have no distinguishable head
-Feed on plankton
using cilia-generated
currents
-Closest relatives to
vertebrates
Vertebrates: chordates with a spinal column
-Distinguished from nonvertebrates by
1. Vertebral column – Encloses and
protects the dorsal nerve cord
2. Head – Distinct and well-differentiated
possessing sensory organs
Vertebrates also have
-Neural crest – A unique group
of embryonic cells that forms
many vertebrate structures
-Internal organs – Liver,
kidneys, endocrine glands, heart
and closed circulatory system
-Endoskeleton – Made of
cartilage or bone
-Makes possible great size
and extraordinary movement
Fishes have the following characteristics
1.
2.
3.
4.
5.
Vertebral column of bone or cartilage
Jaws
Paired appendages
Internal gills
Closed circulatory system
In the Carboniferous period (360-280 MYA), sharks (Class
Chondrichthyes) became the dominant sea predators
 Evolved teeth
 Streamlined
 Lateral Line system.
 A light, flexible, calcified, cartilaginous skeleton, and
paired fins made them superior swimmers
Bony fishes (Osteichthyes) evolved at the same
time as sharks about 400 MYA
 Internal skeleton of bone.
 Swim Bladder
 Gill Cover--operculum
 Actinopterygii—ray-finned fishes. Bones in fins no
muscle. Most fishes of today
 Sarcopterygii—fins with muscles, can function
independently, few fishes, gave rise to….
Amphibians (class Amphibia) are damp-skinned
vertebrates
-First vertebrates to walk on land
Successful invasion of lands by vertebrates required
several adaptations
1. Legs to support body’s weight
2. Lungs to extract oxygen from air
3. Redesigned heart to drive larger muscles
4. Pulmonary veins.
5. Reproduction in H2O to prevent egg drying
6. System to prevent whole body desiccation. The
skin also aids in respiration.
7. Coetaneous respiration.
Over 7000 species of reptiles (class Reptilia) now live
on Earth
All living reptiles exhibit three key features
1. Amniotic eggs, which are watertight
2. Dry skin, which covers body and prevents water
loss
3. Thoracic breathing, which increases lung
capacity
Reptiles, birds and
mammals are
amniotes
The amniotic egg has
four membranes




Chorion – Allows
O2 entry
Amnion – Fluidfilled cavity
Yolk sac –
Provides food
Allantois –
Excretes wastes
Modern reptiles developed two important
characteristics:
1. Internal fertilization: Sperm fertilizes egg before
protective membranes are formed
2. Improved circulation: Oxygen is provided to the
body more efficiently
Comparing the circulatory systems of fish, amphibians, and
reptiles.
Birds (class Aves) are the most diverse of all terrestrial
vertebrates
 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 heat
2. Flight skeleton
-Bones are thin and hollow
-Many are fused (collarbone and
keeled breastbone)
3. Physiological adaptations—efficient respiratory
system.
1. Efficient respiration
-Air passes all the way through lungs in a single
direction
2. 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 structure
2. 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
Prototheria (most primitive)
-Lay shelled eggs, oviparous
-One living group
-Monotremes
Theria
-Viviparous: Young are born alive
-Two living groups
-Marsupials and placental mammals
Egg has chorion and amnion, but no shell
Embryo 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 gave rise to two groups:
 New World Monkies
◦ All arboreal
◦ Flat, spreading noses
◦ Prehensile tails

Old World monkeys and Hominoids (Apes and Humans)
◦ Ground-dwelling or arboreal
◦ None have prehensile tail
The taxonomic group “apes” is paraphyletic
 Some apes are more closely related to hominids than
to other apes.
 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
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
Australopithecus afarensis
Homo--2 MYA: Homo habilis
H. Habilis
Homo erectus
Homo heidelbergensis (oldest)
Homo neanderthalensis and Homo sapiens
H. Hablis was replaced by Homo erectus
Homo 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
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 CroMagnons
Out of Africa Hypothesis
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