Explain how vertebrates are classified into further subgroups. |

Vertebrates are members of the phylum Chordata. Therefore, vertibrates are sometimes called chordates. All chordates contain a spinal cord. One way that scientists classify different subgroups of vertebrates is based on how organisms obtain oxygen. Vertebrates breathe either through their skin, gills, or lungs. Being endothermic or exothermic is another classifier of vertebrate subgroups. Endothermic vertebrates are warm-blooded, while exothermic vertebrates are cold-blooded. The third classifier used to subcategorize vertebrates is reproduction. Some vertebrates reproduce internally, while others reproduce externally. Some vertebrates are oviparous, which means they lay eggs. Others are viviparous, which means they give birth to live young. Vertebrate subgroups include jawless fish, cartilaginous fish, bony fish, amphibians, reptiles, birds, and mammals. A brief explanation is each vertebrate subgroup is provided below.

Jawless fish

Jawless fish belong to the class Agnatha. They do not have jaws, have slender bodies, and have a skeleton that is made of cartilage. Hagfish and lamprey are examples of jawless fish.

Cartilaginous fish

Cartilaginous fish also have a skeleton that is made of cartilage. However, cartilaginous fish do have jaws. Examples include sharks and rays.

Bony fish

Bony fish are fish that have calcified and bony skeletons. Most modern fish are bony fish. Examples of bony fish include pike, trout, bass, and salmon.

Amphibians

Amphibians are cold-blooded chordates that undergo metamorphosis. Amphibians usually transition from a gill-breathing larval stage into a primarily terrestrial adulthood. Frogs, toads, and salamanders are examples of amphibians.

Reptiles

Reptiles are also cold-blooded. The skin of a reptile is dry and scaly. Reptiles lay eggs on land. Snakes, crocodiles, and tortoises are examples of reptiles.

Birds

Birds are warm-blooded vertebrates that have feathers, beaks, and wings. Most birds can fly. Examples of birds are penguins, flamingos, robins, and goldfinches.

Mammals

Mammals are warm-blooded vertebrates that have fur. Offspring of mammals are reproduced internally within the placenta. Mammals have mammary glands from which they feed their offspring milk. Examples of mammals are dogs, cats, rabbits, and humans.