The vertebrates are animals with backbones. So far, nearly 75,000 vertebrate species are known. Here is a look at the 5 groups of vertebrates, their characteristics, and examples of each group.
Characteristics of Vertebrates
Vertebrates share several similar characteristics. In addition to having a backbone, they have a nervous system partially enclosed by the backbone and muscles with bilateral symmetry. A vertebrate has a distinct head and central nervous system, enclosed circulatory system with a heart, and senses that include vision, hearing, and smell. They mainly reproduce sexually.
5 Groups of Vertebrates
The five main groups of vertebrates are fish, amphibians, reptiles, birds, and mammals. There are actually more categories, since bony fish are separate from jawless fish (lampreys and hagfish), cartilaginous fish (sharks and rays), and lobe-fin fish (lungfish and coelacanths).
- Agnatha (Jawless Fish)
- Chondrichthyes (Cartilaginous Fish)
- Sarcopterygii (Lobe-Finned Fish)
- Osteichthyes (Bony Fish)
- Amphibia (Amphibians)
- Reptilia (Reptiles)
- Aves (Birds)
- Mammalia (Mammals)
Closer Look at the 5 Groups
Collectively, fish include cartilaginous fish, like a shark, and bony fish, like a tuna or perch. But, most of the time, when people talk about five groups of vertebrates they only mean the bony fish. Bony fish share several distinctive characteristics:
- Fish are ectotherms. In other words, they are cold-blooded. Their temperature depends on their environment.
- They have gills. Fish live in water get oxygen from gases dissolved in it.
- They have scales and fins.
- Some lay eggs, while others give birth to live young in the water.
Examples of amphibians include frogs, toads, newts, salamanders, and axolotls. Like fish, they are cold-blooded. Unlike fish, they spend part of their lives breathing air. Here are major characteristics of amphibians:
- Amphibians are cold-blooded.
- They spend part of their life in the water, breathing with gills, and part of their life with lungs breathing air. Sometimes the adults still live in the water, while other species live on land.
- Amphibians under a metamorphosis from their aquatic larval form into the adult form with lungs.
- They have thin, moist skin that usually is smooth. They can breathe through their skin as well as their gills or lungs.
- Most amphibians lay jelly-like masses of eggs in water.
Examples of reptiles include turtles, lizards, alligators, and snakes. Like fish and amphibians, they are cold-blooded. Like amphibians, they have four limbs or, in the case of snakes, evidence of limbs. But, amphibians need water, while reptiles are adapted for life on land.
- Reptiles are cold-blooded.
- They have lungs and breathe air.
- Their young resemble small adults. There is no metamorphosis.
- Reptiles have dry, scaly or plated skin.
- Most reptiles lay leathery eggs, although some give birth to live young.
Examples of birds include eagles, sparrows, ostriches, and chickens. Birds are actually the living descendant of dinosaurs. So, all birds are dinosaurs, but not all dinosaurs were birds. Unlike fish, amphibians, and reptiles, birds are warm-blooded. Like reptiles, they hatch from eggs, breath air, and are adapted to life on land.
- Birds are endothermic or warm-blooded. Their metabolism regulates body temperature so that it remains fairly constant.
- Birds have lungs and breathe air.
- While baby birds look a bit different from their parents, there is no metamorphosis.
- Birds have wings, beaks, and feathers.
- They lay hard-shelled eggs.
Examples of mammals include cats, dogs, squirrels, foxes, whales, and humans. Like birds, mammals have lungs and are warm-blooded.
- Mammals are warm-blooded.
- They have lungs.
- Mammals give birth to their young (with a few exceptions) and feed their young milk.
- Mammals have hair or fur.
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