The Vertebrate Genealogy

Chapter 30

What is a chordate?

There are 4 anatomical structures that appear during some point during the animal’s lifetime:1. Notochord – long flexible tube between the

gut and the nerve cord - becomes gelatinous material between vertebrae in humans

2. Dorsal, hollow nerve cord – becomes CNS 3. Pharyngeal slits

4. Muscular postanal tail – most chordates have a tail that extends beyond the anus

What is a chordate?

Survey of Vertebrate Classes

Fishes: Agnatha, Chondrichthyes, Osteichthyes

Tetrapods: Amphibia, Reptilia, Aves, Mammalia

Amniotes: Reptilia, Aves, Mammalia Have a shelled water-retaining egg

Class Agnatha

Sample organisms: Hagfishes, lampreys

Jawless vertebrates Feed by sucking blood

after clamping onto prey or by scavenging

Do not have paired appendages

Class Chondrichthyes

Sample organisms: sharks and rays

Cartilaginous fishes – have relatively flexible skeletons made of cartilage rather than bone

Most sharks are carnivorous and have acute senses

Class Osteichthyes Bony fishes

Have hard skeletons (due to ossification)

Sample organisms: perch, trout Breathe by drawing water over 4-5

pairs of gills covered by operculum (protective flap)

Most bony fishes are oviparous Females lays large numbers of

eggs, fertilization occurs externally

Class Osteichthyes

Class Amphibia The first vertebrates

(tetrapods) on land Amphibians must deposit

their shell-less eggs in water

Sample organisms: frogs & salamanders

Amphibian = “two lives” Tadpole – larval stage Metamorphosis occurs Frog – legs develop

Salamanders – have tails Frogs – do not have tails

The Amniotic Egg The amniotic egg is a

reproductive adaptation that allowed terrestrial vertebrates to complete their life cycles on land

The shell prevents the egg from drying out

4 layers of protection: Amnion – prevents

dehydration, cushions shocks Yolk Sac – stockpile of

nutrients Allantois – disposal sac for

certain metabolic wastes Chorion – gas exchange

Class Reptilia Sample organisms: lizards,

snakes, turtles, crocodiles Reptiles have scales made of

keratin that cover their skin Obtain oxygen with their lungs Fertilization occurs internally

Most reptiles lay amniotic eggs on land

Ectotherms – body temperature fluctuates with the environment

Class Aves

Birds are tetrapods with feathers

Their forelimbs are modified as wings

Sample organisms: owl, sparrow, penguin, eagles

Lay amniotic eggs Endothermic – regulate their

own body temps. Anatomy adapted for flight

Form & function

Class Mammalia Mammals have hair Endothermic Mammary glands that produce milk Most mammals are born, not hatched Three major groups:

Monotremes – lay eggs platypuses, echidnas

Marsupials – complete development in a maternal pouch Kangaroos, koalas, opossums

Placental mammals – complete development within the uterus, joined to the mother by the placenta Sheep, bats, elephants, humans

Paleoanthropology

Paleoanthropology is the study of human origins and evolution

Correcting misconceptions: “Let’s first dispose of the myth that our ancestors

were chimpanzees or any other modern apes. Chimpanzees and humans represent two divergent branches of the anthropoid tree that evolved from a common, less-specialized ancestor.”

Paleoanthropology 1974 – Ethiopia

“Lucy” is an Australopithecus skeleton

3.18 million years old Homo habilis

2.5 million years ago Enlargement of the human

brain Homo erectus

First hominid to migrate out of Africa into Asia and Europe

Taller than H. habilis and a larger brain capacity

Paleoanthropology

2 models of how Homo sapiens evolved

To think about…

“Of the many crises in the history of life, the impact of one species, Homo sapiens, is the latest and potentially the most devastating.”

- Neil Campbell, 4th ed.