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Are vertebrates (which means they have a backbone or spine).

Are endothermic. Also known as “warm-blooded,” endothermic animals regulate their own body temperate which allows them to live in almost every climate on Earth.

Have hair on their bodies.

Produce milk to feed their babies.

1) egg-laying mammals or monotremes
2) pouched mammals or marsupials
3) placental mammals

in placental,  young remain in the mother's body until their body systems are able to function independently.  In marsupials, young must spend time in their mother's pouch
and their young feed on milk from the mother's mammary gland, and in Monotremes, they lay eggs.

A brand-new life begins when an animal is born or hatches from an egg. ... In time, adult animals produce their own young

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Feathers. Feathers are the defining characteristic of Aves, found on every living species of bird and no other class of animal. ...

Wings. All birds have wings, although not all birds fly.

Beak.

Eggs.

Skeleton.

Strisores — night jars, frogmouths, and other nocturnal birds, along with diurnal swifts and hummingbirds.
Columbaves — turacos, bustards, cuckoos, pigeons, sand grouse, and mesites.
Gruiformes — cranes, rails, crakes, Sungrebe, fluff tails, and others.
Aequorlitornithes — shorebirds, flamingos, grebes, gulls, tropic birds, penguins, and other waterbirds.
Inopinaves — all land birds, including hawks, owls, toucans, falcons, parrots, and songbirds.

the differences between the groups are the environments that they live in and the type of food that they eat.

Birds are born inside hard-shelled eggs. For many days to weeks they are protected and kept warm by their parent(s). This is called incubation.

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Cartilagious Fish
Boney Fish
Reptiles
Birds
Mammals

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The first and foremost characteristic of the reptiles is that are cold blooded. They are able to regulate their inner body temperature to the temperature of the environment. They have scaly skins but absence of hair or fur. The scales of the reptiles develop as a surface cells filled with Keratin.

Crocodilia — crocodiles, gharials, caimans and alligators: 23 species.

Sphenodontia — tuataras from New Zealand: 2 species.

Squamata — lizards, snakes and amphisbaenids ("worm-lizards"): about 7,900 species.

Testudines — turtles and tortoises: approximately 300 species.

the differences between the different groups are the places that they live and their food that they eat.

Great diversity marks the reptile family, which includes snakes, lizards, alligators and turtles. ... They have similar life cycles that begin as eggs and progress to hatchlings and then to juveniles before they arrive at the adult stage of life.

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1. Body spines are modified scales.

2. Protective spines are common in slow-swimming fishes and others that need to protect themselves without moving.

3. Some fishes actively engage spines.

Most surgeonfishes (family Acanthuridae) have mobile, razor-sharp precaudal fin spines that they use to protect themselves.

The triggerfishes (family Balistidae) have three dorsal spines that lock together. These spines may allow a triggerfish to securely lodge itself between rocks and keep predators from swallowing it.

Some pufferfishes (family Tetraodontidae) have spines that cover the entire body. The spines lie flat until the pufferfish inflates its body.

It is divided into two classes: Actinopterygii − Ray-finned fish — contains most of the superclass's species. Sarcopterygii − Lobe-finned fish.

the difference between the groups is the fins.

there is great variation in the development stage at which offspring are released: fertilized eggs, larvae, juvenile fish, or even sexually mature adults. Oviparous bony fishes release eggs, and the developing embryo is nourished by a yolk sac.

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Paired fins.

Paired nostrils.

Scales.

Two-chambered hearts.

Skeletons made of cartilage rather than bone. Cartilage is supportive tissue that does not have as much calcium as bones, which makes bones rigid. Cartilage is softer and more flexible than bone.

Cartilaginous-any member of the diverse group of cartilaginous fishes that includes the sharks, skates, rays, and chimaeras

each group is different in that it is on a different part of the food pyrymid, with sharks being on the top.  Also, their bodily makeups are a lot different.

There is no parental care after birth; however, some Chondrichthyes do guard their eggs. Also, skates typically have a prominent dorsal fin while the dorsal fin is absent or greatly reduced in rays. Cartilaginous fish all breathe through 5 to 7 gills, depending on the species.