People often wonder about the origins of animals. There is a lot of evidence that animals developed from plants and even prehistoric creatures such as dinosaurs were plant-eating creatures. The fossil record shows that these animals existed in the Earth’s early Mesozoic era millions of years ago. How did animals evolve?
Animals are multicellular, living organisms in the Kingdom Animalia. They are characterized by a nervous system, a digestive system, a chest, a hind leg, a head with a skull, teeth, and fins. With very few exceptions, animals breathe oxygen, consume food, can breed internally, move, can regenerate, and reproduce. In the distant past, fish lived in rivers and lakes and were part of the communities that surrounded modern towns. They were carnivores, but in the Neolithic age, they began to be hunters, and by the Early Mesolithic age, they were starting to produce milk teeth.
One of the most interesting evidences of animal evolution is the fact that whales have their brains in the back of their mouths! While this might seem to be a strange detail, it is actually an example of convergent evolution. Convergent evolution is when one animal develops characteristics that are independent of its own ancestors.
How did animals develop over time? The major animal groups are trichopterians, cetaceans, amphibians, birds, mammals, and reptiles. Over the last million years or so, there has been a great expansion of the animal kingdom. One of the biggest expansions is in land animals, where land animals like dinosaurs and small whales have become very large. This has caused some major evolutionary changes, especially in relation to how animals look.
Insects are the most common of all animals. They have developed wings, which allow them to fly, since they do not have legs. Most insects have wings in only one area, but there are some with two, or even three flaps of wings. They also have various mouth parts, such as mouthfuls, which allow them to bite into things. Most insects are arboreal, meaning they walk around on the ground, but there are some aquatic insects that have developed a tail for swimming.
The last group of animals is aquatic. Fish, amphibians, crustaceans, and sharks are all classified as aquatic animals. They are classified as either semi-aquatic or fully-aquatic depending on whether or not they breathe through lungs. Most fish don’t breathe through their lungs, while crustaceans and sharks do.