How many species of animals are there? What is the largest animal, and how are we related to rats? Peter Holland, the author of The Animal Kingdom: A Very Short Introduction, tells us 10 things everyone should know about the animal kingdom, and how we humans fit in.
- An animal must have several characteristics to be an animal: it has a body built of many cells, it gets the energy necessary for life by eating other organisms, it has the ability to move, and can sense its environment.
- Animals are a natural group, or clade, descended from a shared common ancestor. This clade is called the Animal Kingdom, or Metazoa.
- Animals originated in the sea, but they have colonized fresh water, land, and air. Some, such as flukes and tapeworms, have invaded the bodies of other animals, while a few, such as dolphins, have returned to sea again.
- Nobody knows how many species of insects exist; estimate range from a few million to over 30 million. At least 800,000 different species have been described and named formally.
- The “big four” of the insect orders, accounting for over 80% of prescribed species are the beetles; butterflies and moths; bees, wasps, and ants; and flies.
- Mostly, animals are divided into two groups: vertebrates and invertebrates. Millions of invertebrate species are described, whereas only around 50,000 different vertebrates are known.
- Large size, efficient blood circulation, dynamic skeleton, intricate brain, protective skull, and elaborate sense organs are the features that set vertebrates apart.
- There are only five living species of monotreme, or egg-laying, mammal: the platypus, and four types of spiny anteater. All other mammals are “therians” and have live birth.
- Humans are opportunist omnivores, just like mice and rats. That means that they eat pretty much anything that is available to them at the time.
- The largest and heaviest that has ever lived is the blue whale. It weighs 150 tons and can be up to 30 meters long — and it is still alive today.
Featured image credit: lion-portrait-animal by Sponchia. Public domain via Pixabay.