1. Domain: This is the broadest level, encompassing all life on Earth. Animals belong to the domain Eukarya, which means their cells have a nucleus.
2. Kingdom: Animals belong to the Animalia kingdom, meaning they are multicellular, heterotrophic (meaning they obtain nutrients from consuming other organisms), and typically mobile.
3. Phylum: This level groups animals based on fundamental body plan features. Some examples include:
* Chordata: Animals with a notochord (a flexible rod supporting the body) at some point in their development (e.g., vertebrates like fish, amphibians, reptiles, birds, and mammals).
* Arthropoda: Animals with an exoskeleton, segmented body, and jointed appendages (e.g., insects, spiders, crustaceans).
* Mollusca: Soft-bodied animals often with a hard shell (e.g., snails, clams, squid).
4. Class: Animals within a phylum are further classified based on more specific features. For example, within Chordata:
* Mammalia: Animals with fur, mammary glands, and give birth to live young.
* Aves: Animals with feathers and wings.
5. Order: This level groups animals within a class based on shared characteristics. For example, within Mammalia:
* Primates: Animals with grasping hands and feet, large brains, and typically five fingers and toes.
* Carnivora: Animals that primarily eat meat.
6. Family: Animals within an order are further classified based on shared characteristics. For example, within Primates:
* Hominidae: Great apes like humans, gorillas, chimpanzees, and orangutans.
7. Genus: This level groups closely related species. For example, within Hominidae:
* *Homo* (humans)
8. Species: This is the most specific level of classification, defining a group of organisms that can interbreed and produce fertile offspring. For example, within the genus *Homo*, the species *Homo sapiens* refers to modern humans.
In addition to these major levels, scientists also use other characteristics to further refine classification:
* Anatomy: Physical structures like the skeletal system, digestive system, and circulatory system.
* Physiology: How an animal's body functions, including metabolism, respiration, and reproduction.
* Embryology: The development of an organism from a fertilized egg.
* Genetics: The study of genes and their inheritance, which can reveal evolutionary relationships.
* Behavior: How an animal interacts with its environment and other organisms.
* Fossil record: The study of preserved remains of past organisms can provide information about evolutionary relationships and the history of life on Earth.
By using a combination of these criteria, scientists constantly refine and update the classification system to reflect the most current understanding of animal diversity and evolution.