A pet is any domesticated animal that can be kept as a pet. Pets are commonly used by people for companionship, companion pet, or simply a fun recreational activity. There are four broad types of domestic animals that can be kept as pets: cats, dogs, birds, and mammals.
Animals are multicellular, meaning they are alive. The majority of animals are vegetarian, but there are some omnivores that feed on vegetation, fruits, seeds, and small animals such as insects, fish, and worms. Most animals breathe air, eat organic matter, can move, reproduce internally, and can survive in an oxygen enriched environment. The four different categories of animals make up the classifications of domestic animals. Each group has characteristics of its own, although they generally do not display the same set of traits in all four categories.
Insects belong to the Kingdom Animalia, the segment of the vertebrate animal family with the highest taxonomic rank. Virtually all insects have wings, although some insects are only two celledes with their wings spread widely apart. Some insects are wingless, such as aphids, while others are winged, such as flying insects. In both cases, an animal in this kingdom is capable of flight, although it may not be capable of swimming.
Archaeology is the study of animal remains over time, and dinosaurs are a good example of how much can be learned about prehistoric animals by looking carefully at their skeletal remains. Dinosaurs are the most common prehistoric animal species, with millions of years of fossils from which to learn about their habits, feeding patterns, lifestyle, and relationships to other animals. Nearly all dinosaurs died off around 65 million years ago, but a small number survived the extinction, resulting in a smaller number of the dinosaurian family tree. One problem that arises from studying fossils is that they are composed of protein. Therefore, it is difficult to extract DNA from fossils.
The class of animalia includes not only insects but all living things in this world, as well as many classifications of living things (e.g., protozoa, bacteria, fungi, etc.). Every living animal species belongs to at least one class of animalia, although classifications sometimes become obsolete as a result of evolution. Insects are part of the animal kingdom. The term animal therefore refers to any living thing with both an exoskeleton and a soft abdomen and mouth. An invertebrate is a living animal that does not belong to any class of animalia. The invertebrates are, as we see, the true inhabitants of the earth.
A group of animals that are considered true land animals are called vertebrates. A class of animals that are considered true water animals are called aquatic. There are two basic groups of animals (e.g., land and water), each having many subtypes: land-land and water-water.