a major group of multicellular, eukaryotic organisms of the kingdom Animalia. Their body plan eventually becomes fixed as they develop, although
some undergo a process of metamorphosis later on in their life. Most animals
are motile, meaning they can move spontaneously and independently. Animals are
also heterotrophs, meaning they must ingest other organisms for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago.
have divided animalss into two main groups: Vertebrates
(animals with a backbone) and Invertebrates
(animals without a backbone)
Animals with backbones can be divided into five more groups: Mammals, Birds, Fish, Reptile, Amphibians
What Is a Mammal?
The word mammal comes from the Latin mamma, meaning breast, because female mammals produce milk to nurse their babies. Nearly all mammals give birth to live young, and all are warm-blooded, maintaining a near-constant body temperature regardless of environmental conditions. They are vertebrates and use lungs to breathe air and are the only animals that grow hair. Mammals are the only animals with hair or fur that protects it agains the elements - heat, cold, wind, rain, bacteria, and even infection. Mammals probably appeared on Earth some 200 million years ago.
What Is a Bird?
There are about 10,000 bird species, found in every shape and size, from the tiny hummingbird to the majestic condor. They occur in all the colors of the rainbow and are loved for their musical songs. Some birds can even mimic human speech. All birds lay eggs to incubate their young, and all have feathers—a trait no other animals can claim. Birds also have wings, evolutionary adaptations of ancient forelimbs. Most use their wings for flight, but others, like ostriches and penguins, are grounded.
What Is a Fish?
Fish are ancient water-dwelling creatures found all over the globe. They are the world's oldest vertebrates, with the first fish appearing some 500 million years ago. Today more than 24,000 species populate the waters of the world. Fish are vertebrates and breathe using gills, which draw oxygen from the water and into the bloodstream. Most have bony skeletons, though sharks and rays have skeletons made of cartilage. Nearly all reproduce by laying eggs.
What Is an Amphibian?
Amphibians lead double lives—one in water and one on land. Many begin life with gills, then develop lungs as they age. They are vertebrate animals that include frogs, toads, salamanders, and newts as well as odd, wormlike caecilians (seh-SILL-yuns). They are cold-blooded, using the environment to regulate their body temperature. Early amphibians were the first animals to leave the sea and venture onto land, forming a crucial link from fish to terrestrial reptiles.
What Is a Reptile?
Reptiles have been around for 300 million years, and during the age of the dinosaurs, they ruled the Earth. Those days are long gone, and those giants have vanished, but some 6,500 species of reptiles still thrive today. Crocodiles, snakes, lizards, and turtles are all reptiles. Most reptiles live on land, and most lay eggs. They are vertebrates, and, unlike any other animals, are covered in scales. They are cold-blooded, and regulate their body temperature by seeking or avoiding the sun's heat.
Etymology of animals:
The word "animal" comes from the Latin word animale, neuter of animalis, and is derived from anima, meaning vital breath or soul.
Characteristics of animals:
Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and usually multicellular, which separates them from bacteria and most protists. They are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. In most animals, embryos pass through a blastula stage, which is a characteristic exclusive to animals.
Structure of animals:
Animals have bodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and nerve tissue, which sends and processes signals. All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. During development it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible.
energy sourcing of animals:
Predation is a biological interaction where a predator feeds on its prey. Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of the prey. Selective pressures imposed on one another has lead to an evolutionary arms race between prey and predator, resulting in various antipredator adaptations.
Most animals feed indirectly from the energy of sunlight. Plants use this energy to convert sunlight into simple sugars using a process known as photosynthesis. When animals eat these plants (or eat other animals which have eaten plants), the sugars produced by the plant are used by the animal. They are either used directly to help the animal grow, or broken down, releasing stored solar energy, and giving the animal the energy required for motion.