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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.

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Monotremes
Marsupial
Placentals

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Distinction of How Groups are Different 

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Distinction of How Groups are Different 

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Monotremes:
Monotremes are members of the mammalian order Monotremata. They are the only mammals that don’t give birth to live young. Instead, they lay eggs. Despite this, monotremes still nurse their young with milk, have hair, and possess three bones in the middle ear: features that identify them as being mammals. Scientists believe that they were ‘left behind’ by the branch of mammals that would go on to become the marsupials and placental mammals. This is why the monotremes still lay eggs like their reptilian ancestors.

There are only five monotreme species: the platypus, and four species of echidna.

Marsupials:
A marsupial is a member of the infraclass Marsupialia. (Infraclass is an intermediate classification category that comes below class.) Marsupials are mammals whose young are born in a relatively undeveloped state. After being born, the young (called ‘joeys’) crawl into a special pouch in the mother’s body. Here they undergo further development, and have access to their mother’s milk. Most marsupials live in Australia, but some are found in the Americas.

Example of marsupials include: red kangaroo, koala, Tasmanian devil, and Virginia opossum.

Placentals:
A placental mammal is a member of the infraclass Placentalia. Placental mammals give birth to live young. While in the womb, the developing fetus receives nourishment from an organ called a placenta.

Examples of placental mammals include: tiger, blue whale, vampire bat, and man.

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Warm blooded animals included in the Amniota clade are collectively known as Mammals. Animals in the class Mammal are distinguished from other amniotes like birds, reptiles and amphibians by various physical features including the presence of hair, the neocortex region in their brains and the presence of mammary glands in females. The modern name "Mammal" is derived from the class's scientific name Mammalia and was first coined by Swedish zoologist Carl Linnaeus in the year 1758.

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They are born and then they grow up.

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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.

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Strisores
Nightjars
Frogmouths

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Distinction of How Groups are Different 

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Distinction of How Groups are Different 

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1. Possession of a beak

2. Skeletal structure

3. Pneumatic characteristic

4. Presence of air sacs

5. Possession of feathers

6. Possession of wings

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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.

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they are born (either alive from their mother or hatched from eggs)

they grow up

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All reptiles have a backbone, which means they are vertebrates.

All reptiles produce eggs. Most reptiles lay hard-shelled eggs, but a few give birth to live young.

All reptiles have scales or scutes

Reptiles are ectothermic or cold-blooded, which means they cannot control their own body temperature.

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Crocodilia
Sphenodontia
Squamata
Testudines

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Distinction of How Groups are Different 

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Distinction of How Groups are Different 

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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.

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Cold-bloodedness. Reptiles are cold-blooded

Respiration. All reptiles possess lungs, and none passes through an aquatic larval stage with gills, as do many of the amphibians

Skin and Scales

The Amniote Egg

Internal Fertilization

The Heart

Metanephric Kidney

Skull.

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they are born (either alive from their mother or hatched from eggs)

they grow up.

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Bony fish are members of the class osteichthyes, and are defined by their calcified skeleton, hinged jaw, gill arches, gill filaments, and gill rakers. They also have an operculum for pumping water across the gills and swim bladders to control buoyancy, as well as mucous-lined scales.

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Bony Fish
Cartilaginous Fish

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Distinction of How Groups are Different 

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Distinction of How Groups are Different 

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There are two types of fish that usually are contentious, and give a lot of people a hard time telling apart. If you can learn the differences between these two types of fish, it can be very easy for you to understand and tell them apart where necessary. Technically, the most obvious disparity between bony vs cartilaginous fish comes from the fact that the skeleton of bony fish is made of bones alone, while that of cartilaginous fish is made of cartilage.

Bony Fish:

Their endoskeleton is entirely made of bone

They have anterior tip mouth opening

They can either be fresh water or marine water fishes

Their exoskeleton is made up of cycloids (thin bony plates), aligned based on whether the outer edges are spiny or smooth

They have an operculum on either side of their gills

They possess an air bladder that also performs hydrostatic functions

Their tail fin is homocercal

They fertilize their eggs externally

Cartilaginous Fish:

Their endoskeleton is primarily made of cartilage

Their exoskeleton is made of placoid (very small denticles coated with lots of sharp enamel)

The buccal cavity of these fishes is ventrally positioned

The position of their tail finds is heterocercal

On either side, they have 5 gills that are overly exposed, so they do not have an operculum

Their mode of fertilization is through internal mechanisms

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Bony fish are members of the class osteichthyes, and are defined by their calcified skeleton, hinged jaw, gill arches, gill filaments, and gill rakers. They also have an operculum for pumping water across the gills and swim bladders to control buoyancy, as well as mucous-lined scales.

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Changes in the duration of sunlight (called photoperiod) can stimulate some species of bony fishes to begin reproduction.

Temperature change may trigger breeding in temperate and subpolar areas.

Other factors that may affect reproduction are presence of the opposite sex, currents, tides, moon stages, and presence of spawning areas.

Some bony fishes may spawn many times a year.

Many bony fishes reproduce once a year until they die.

Other bony fishes may reproduce only once during their lifetime. Pacific salmon (family Salmonidae) reproduce only once during their five-year lifespan, then die soon after.

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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.

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Elasmobranchii
Holocephali

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Distinction of How Groups are Different 

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Distinction of How Groups are Different 

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Elasmobranchii and Holocephali. The elasmobranchs include sharks and rays of which there are more than 800 species, whereas the Holocephali (chimaeras) is a much smaller group of about 40 species.

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Chondrichthyan males have a pelvic clasper, a specialized organ used in mating. Unlike most bony fishes, all chondrichthyans have internal fertilization. Reproduction can be oviparous (laying eggs, notably the "mermaid's purses" found on beaches), viviparous (live-bearing), or ovoviviparous (eggs carried within the mother).  They are particularly sensitive to low-frequency vibrations such as those emitted by injured animals. Sound is detected through the ears and through the lateral line , a series of fluid-filled canals along the head and sides of the body that contain sensory cells sensitive to vibrations. As in many nocturnal mammals, the inside of a shark's eye is covered with a tapetum , a membrane that reflects light back into the eye, making it easier to see in dim light. Unlike most fishes, sharks can reduce and expand their pupils. In some species, the eyes are protected during feeding by the nictitating membrane, a structure similar to an eyelid. The Elasmobranchi group has external nostrils on the lower side of the body; because of them, sharks can detect tiny concentrations of substances such as blood, which allows them to scent prey from distances of several hundred feet. Finally, sharks can detect electrical signals via the ampullae of Lorenzini, which are specialized organs distributed over a shark's head that detect changes in electrical currents. Sharks use these to sense the electrical fields emitted by the heart and muscles of their prey.

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Fishes that lack bone. Instead, the skeleton is composed of cartilage that is partly calcified.
In addition to the difference in their skeletons, cartilaginous fish have gills that open to the ocean through slits, rather than the bony covering that is present in bony fish.

Different shark species may have different numbers of gill slits.

Cartilaginous fish may also breathe through spiracles, rather than gills. Spiracles are found on top of the heads of all rays and skates, and some sharks. These openings allow the fish to rest on the ocean bottom and draw oxygenated water in through the top of their head, allowing them to breathe without breathing in sand.

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Cartilgious Fish
Boney Fish
Reptiles
Birds
Mammals