vertebrates v1.0

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

2. Cephalochordata

3. Vertebrata

Nonvertebrates

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. Vertebral column of bone or cartilage2. Jaws3. Paired appendages4. Internal gills5. 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

1.1. LegsLegs to support body’s weight2.2. LungsLungs to extract oxygen from air3.3. Redesigned heartRedesigned heart to drive larger muscles4.4. Pulmonary veinsPulmonary veins. . 5.5. Reproduction in HReproduction in H22OO to prevent egg drying6. System to preventprevent whole body desiccation. desiccation. The skin The skin

also aids in respiration. also aids in respiration. 7.7. Coetaneous respiration. Coetaneous respiration.

Over 7000 species of reptiles (class Reptilia) now live on Earth

All living reptiles exhibit three key features1. Amniotic eggs, which are watertight 2. Dry skin, which covers body and prevents water loss3. Thoracic breathing, which increases lung capacity

Reptiles, birds and mammals are amniotes

The amniotic egg has four membranes

Chorion – Allows O2 entry

Amnion – Fluid-filled 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 heat2. 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 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

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 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 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 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

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

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