All chordates share the 4 features at some stage of their development:

Is a flexible skeletal support rod embedded in the animal’s back

Bone and cartilage are both part of the vertebrate endoskeleton

The Agnatha are the oldest class of vertebrates that includes sharks.

Bony fish, have skeletons made of bone.

Were the first vertebrates adapted to live both in water and on land.

Are animals that have hair, mammary glands, and three middle ear bones

Fish use specialized organs called gills to take in the oxygen dissolved in water.

Amphibians use many strategies to keep their eggs wet, including

Tadpoles are aquatic larvae of frogs

Metamorphosis is the change in form and habits of an animal.

Reptiles were the last amniotes.

Viviparous reptiles deposit their eggs into an external nest, and the eggs develop completely independent of the adult reptile

All living reptiles are ectotherms which body temperature changes based on the surrounding environment

Most turtles are omnivorous so they eat plants as well as animals

They are all semiaquatic predators that live in swamps and rivers in the tropics

Mammary glands are specialized glands that produce milk.