Biology 102 - Chordates

I. Phylum Chordata

A. Characteristics

1. Notochord - rod of stiffening tissue

2. Dorsal, hollow nerve cord

3. Pharynx with gill slits in the lateral walls

B. AInvertebrate@ Chordates

1. Urochordata (tunicates) - sea squirts

a. larvae with chordate characteristics

b. adults are sessile

c. filter feeders

2. Cephalochordata (lancelets)

a. filter feeders

b. adult has chordate characteristics

C. Vertebrates - animals with backbones

1. Three chordate traits plus vertebrae of bone or cartilage

2. Evolutionary trends

a. cephalization

(1) nervous system

(2) jaws

b. fins - stabilize and guide

c. filter feeders-to-bulk feeders

d. freshwater-to-land

(1) legs

(2) lungs

D. Agnatha - jawless fishes (ostracoderms)

1. filter feeders

2. Armored body

E. Gnatostoma - jawed fish

1. Placoderms - primitive jawed fishes

a. jaws from gill supports

b. paired fins - pectoral and pelvic

2. Lampreys and hagfishes

F. Chondrichthyes - cartilaginous fishes

1. Skeleton of cartilage

2. Scales of bone - like teeth

G. Osteichthyes - bony fish

1. Skeleton of bone

2. Mostly gills for gas exchange

3. Gas bladder for flotation

4. Ray-finned fishes

a. smaller fins with little bony supports

b. great diversity

5. Lobe-fined fishes - living fossils

a. larger fins with bony supports

b. gas bladder connected to pharynx

c. ancestors of land dwelling vertebrates

d. lung fishes

H. Amphibia

1. Stronger bony skeleton

2. Legs--the paired appendages

a. little muscle

b. bend vertebral column to walk

3. Lungs

4. Reproduce in water

5. Diversity of amphibians

a. salamanders

b. frogs and toads

I. Reptiles

1. Completely terrestrial

2. Reproduce on land

a. internal fertilization

b. embryo protected in an egg

c. embryo with amnion - protective sac

3. Kidneys modified to conserve water

4. Scaly skin

5. Diversity of reptiles

a. synapsida - early form that evolved into mammals

b. turtles

c. ichthyosaurs and plesiosaurs swimming and fish-like

d. crocodilians, pterosaurs, dinosaurs and birds

e. snakes, lizards and tuatara

J. Aves -- the birds

1. Really a group of reptiles

2. Flight

a. feathers

b. modified skeleton and muscles

K. Mammals

1. Evolved from synapsid line of reptiles

2. Characteristics

a. mammary glands

b. hair

c. modified teeth for chewing

3. Primitive mammals -- platypus and spiny anteater

4. Marsupials - pouched mammals

a. young born tiny, hairless and blind

b. finish development in the pouch

c. found primarily in Australia

d. adaptive radiation similar to rest of mammals

5. Placental mammals

a. young develop in uterus

b. placenta for transfer of nutrients, gases and wastes

c. adaptive radiation (Eocene-Oligocene)