Phylum: Chordata

Chapter 34

What you need to know!

The 4 chordate characteristics. Adaptations that allowed animals

to move onto land. Traits which distinguish each of the

following groups: Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Birds, and Mammalia.

How the 3 classes of mammals differ in their reproduction.

Characteristics of all Chordates

1. Notochord: Longitudinal, flexible rod located between the digestive and the nerve cord

2. Nerve cord (dorsal, hollow): eventually develops into the brain and spinal cord (arthropods ventral)

3. Pharyngeal slits: become modified for gas exchange, jaw support, and/or hearing

4. Muscular, postanal tail

Neurulation (Vertebrates)

Neural Tube: dorsal folding of the ectoderm forming a hollow nerve tube

Neural Crest: embryonic cells (mesoderm) near the neural tube that migrate throughout the body to form special bones like the jaw and cranium

Animation: http://

learningobjects.wesleyan.edu/neurulation/animation.php

Macroevolutionary Trends

Vertebrata Pronounced Cephalization: concentration

of sensory and neural equipment in the head

Cranium (skull): encloses brain Endoskeleton: notochord becomes

cartilage or bone (vertebral column) enclosing the hollow nerve chord Bone is more advanced than cartilage

Hinged Jaw Closed circulatory system with a ventral

chambered heart

Land Adaptations Gills lungs Paired lobed fins legs (tetrapod) Amniotic Egg (shelled egg): several

extraembryonic membranes that are not part of the embryo, but produced by embryonic tissue: Amnion: protects embryo, contains

amniotic fluid for shock absorption Allantois: forms extra sac for waste disposal

and gas exchange Yolk Sac: nutrient stockpile Chorion: gas exchange

Amniotic Egg

Major Divisions Fish

Class Chondrichthyes: flexible endoskeletons and jaws (i.e. shark and stingray)

Class Osteichthyes (bony fish): most numerous vertebrates, boney endoskeleton, scales (i.e. trout and salmon)

Class Amphibia: gas exchange across skin (most use lungs), soft water-based eggs, larvae have two-chambered hearts, adults have three chambers (i.e. frogs and salamanders)

Class Reptiles: gas exchange in lungs, intercourse, amniotic egg, scales (keratin), ectothermic, three chambered heart (i.e. turtles, lizards, and alligators)

Major Divisions

Birds (subdivision of reptiles): amniotic eggs, scales on legs, wings, feathers, endotherms, four chambered heart

Class Mammalia: milk from mammary glands, hair, endotherms, four chambered heart, large brains, teeth

Mammalian Subdivisions

1. Monotremes: egg laying mammals (i.e. platypuses and spiny anteaters)

2. Marsupials: born early, complete embryonic development in a pouch (i.e. kangaroos and opossums)

3. Placental mammals (eutherians): long pregnancy, fetus develops in the uterus (i.e. dogs and humans)