Discovering The Animal Kingdom: A guide to the amazing world of animals

By Marianne Taylor

Discover the wonders of the natural world and the animals that inhabit it in this stunningly visual hardcover guide.

Nature writer Marianne Taylor guides readers through the development of life on earth, from the first living cells to the astonishing diversity we see in species today. Journeying from the invertebrates, including spiders, crustaceans and insects, to fish, amphibians, reptiles, birds and mammals, this fascinating book explores the animal kingdom is all its oddity and splendour. A numbers of feature spreads give a deeper focus on themes such as coral reefs, the importance of insects in ecology and the era of the dinosaurs.

Sections include:
• Animal Evolution
• Invertebrates: insects, molluscs,
• Vertebrates: fish, reptiles, birds, mammals
• Ecology and conservation

Featuring superb full-color wildlife photography as well as a range of diagrams and infographics, this is a captivating guide to the wonders of the animal kingdom which can be enjoyed by the whole family.

ABOUT THE SERIES: Arcturus' Discovering... series brings together spectacular hardback guides which explore the science behind our world, brought to life by eye-catching photography.

• Language: English
• Publisher: Arcturus Publishing
• Release date: Dec 1, 2021
• ISBN: 9781398817050

Marianne Taylor

Marianne Taylor is a writer and editor, with a lifelong interest in science and nature. After seven years working for book and magazine publishers, she took the leap into the freelance world, and has since written ten books on wildlife, science and general natural history. She is also an illustrator and keen photographer, and when not at her desk or out with her camera she enjoys running, practicing aikido, and helping out at the local cat rescue center.

Book preview

ANIMAL EVOLUTION

The wonderful diversity of animals that inhabit our planet today has come about through evolution. This near-miraculous but biologically inevitable process has shaped animals to thrive in every kind of natural environment, and continues to do so today.

A Wolf giant tortoise (Chelonoidis becki) on the rugged west slope of Wolf Volcano, Isabela Island, Galapagos. Many hybrids of mixed parentage with different shell shapes found on different islands in the archipelago, thanks to early explorers moving the animals from island to island.

// The origins of Earth and the solar system

The universe came into being about 13.75 billion years ago—we think. How did we conclude this? When humankind devised telescopes that could look beyond the Milky Way—our home galaxy—we discovered that many other galaxies existed. We also found that all of the galaxies we can see are moving away from each other—evidence that the universe is expanding as time passes. By looking at the rate of expansion, we can imagine that process in reverse, and work backwards to a time when all of the matter that today forms all of the stars and planets was condensed into a single point.

In its first milliseconds of existence, the universe was extremely hot and expanding in all directions incredibly rapidly. This is sometimes described as the big bang, though some scientists say it would be more helpful to picture this process as the big stretch—a rapidly inflating balloon, rather than a chaotic explosion. Exactly how and why this happened is still mysterious, and these may be questions we’ll never be able to answer. But what happened—and still happens—to matter in the expanding and fast-cooling universe is (a little) easier to understand. Over time, the tiniest fundamental particles begin to coalesce into atoms, and atoms come together under the force of gravity to form clouds of gas. When a cloud of gas contracts under gravitational pressure, it turns into a swirling disc. Its gravitational center forms a star. The remaining material circles (orbits) the star, and through gravity this material may coalesce into planets (and their moons).

Our home star is the Sun. It is a vast sphere of gaseous plasma, generating enormous amounts of light and heat. It is orbited by eight planets, themselves orbited by a total of more than 200 moons (Saturn alone has at least 82 moons), and by countless smaller objects – planetoids, meteors, asteroids and comets. The planets nearest the Sun (Mercury, Venus, Earth and Mars) are small and rocky in nature, while the more distant bodies (Jupiter, Saturn, Uranus, and Neptune) are large and gaseous. The Earth orbits about 93 million miles (149.6 million km) out from the Sun. Its own gravity holds a cloud of gas—an atmosphere – around it. Without its atmosphere, Earth’s average surface temperature would be about -0.4ºF (-18ºC), but the atmosphere traps enough of the Sun’s heat to maintain an average surface temperature of 57.2ºF (14ºC).

At this point in our solar system’s lifespan, our planet sits comfortably within the habitable zone (shown by the blue ring), but as the Sun ages and grows, the zone will move away to the outer planets.

Life probably began in warm, shallow water, and this habitat is still extremely rich in life of all kinds.

This nebula, 900 light years from Earth, is a cloud of gaseous molecules, possibly the remnants of a large star that exploded (supernova). New galaxies form from large amounts of this kind of interstellar dust.

Does life exist in other worlds?

Earth is the only planet in our solar system known to hold life, and scientists believe that this is because its temperature permits the existence of liquid water, on which every known living thing depends. However, there is no doubt at all that there are other solar systems – in our galaxy and beyond – that hold planets and moons that have liquid water and in many other ways will be just like Earth. Astronomers estimate that the Milky Way alone may contain as many as 40 billion such planets. So, the odds are very good that life exists elsewhere in the universe.

// A timeline of life on Earth

The planet Earth formed about 4.54 billion years ago, making it about one-third the age of the universe itself. The newborn Earth was a hostile and volatile place. Its gravity was pulling in other smaller objects that were orbiting the Sun, and these collisions caused violent volcanic activity. The biggest collision of all, with a hypothesized Mars-sized object known as Theia, produced the cloud of debris that went on to form our planet’s only moon.

Over time, Earth cooled down, and its molten rock surface condensed into a solid crust. Volcanic eruptions released various gases, which went towards forming Earth’s first atmosphere. This contained virtually no oxygen, but was made mostly of carbon dioxide, with some nitrogen, methane, ammonia and hydrogen, and water vapor. When the planet’s surface had cooled enough, the water vapor condensed and rain fell, forming rivers and oceans on top of the rocky crust. The first forms of life evolved in these waters. Some of these simple bacteria-like microorganisms were capable of photosynthesis – using carbon dioxide, water, and sunlight to produce glucose, a simple sugar that is a key energy source used by nearly all living things. The chemical reaction of photosynthesis releases oxygen as a by-product.

Thanks to these first photosynthesizers, oxygen accumulated in Earth’s atmosphere. The process of breaking down glucose to release energy can be done with oxygen (aerobic respiration) or without oxygen (anaerobic respiration). Before photosynthesis, nearly all respiration was anaerobic. However, because aerobic respiration is a much more efficient process, the first simple organisms that could use oxygen for their respiration began to proliferate and to out-compete their anaerobic cousins. This was the trigger for an explosion of oxygen-consuming life on Earth, which led to the evolution of complex life forms.

// How life began

One of the greatest mysteries that scientists grapple with is the origin of life—and even the very nature of life. Why can’t we bring a dead animal back to life, even though all of its bodily systems are still there? The spark of life that’s required to do this is elusive, and indeed seems to be almost mystical. How can something like this have appeared from non-living material?

What we understand as alive does change, though, depending on what we are looking at. All of the animals familiar to us seem obviously alive—we can see them breathe, move, eat, have offspring, and eventually die. But can we consider an organ or a single cell in that animal’s body to be alive in the same way? And what about other organisms? It’s not as easy to see these same signs of life in a plant, a mushroom, or a bacterium—and what about a virus?

Biologists today recognize several distinct characteristics of life that must be fulfilled for an entity to be regarded as a living thing. The most widely used list comprises the following seven traits:

• They respond to their environment in some way;

• They grow and change in some way;

• They can reproduce themselves;

• They have metabolic processes that build up and break down molecules (for example, respiration);

• They maintain a stable internal environment

• They are made of one or more membrane-bound cells;

• They pass their traits on to their offspring, through genetic inheritance.

An animal, a plant, a mushroom and even a bacterium displays all seven characteristics. A virus, however, does not – for example, it neither grows nor does it have a cellular structure, so it does not fully qualify as a living thing.

Looking at the structure of a virus can help us imagine what early life (or protolife) on Earth might have been like. The simplest types of virus consist of some RNA (ribonucleic acid, a molecule that can replicate itself, and tells a cell how to build proteins) in a protein coat. Is it possible that strands of RNA could have existed in a free state, replicating themselves and being almost-alive? Their building blocks – simple molecules made of carbon, hydrogen, oxygen, and nitrogen, are the nucleic acids. Laboratory studies show that it is possible to create nucleic acids by applying lots of energy to water that is rich in dissolved ammonia, methane and carbon dioxide, as would have existed in the first oceans on the planet. That energy could have come in the form of ultraviolet radiation emitted by the Sun.

Many scientists agree that this RNA world scenario may well be how life first appeared. The simplest modern living things – the bacteria and the similar-looking archaebacteria or archaea – are known as prokaryotes. They are little more than a tangled ring of DNA (deoxyribonucleic acid, the double-stranded version of RNA) held inside a membrane formed of fats and proteins. Life forms with complex cell types (whether they are single-celled or multicellular organisms) are known as eukaryotes. A eukaryote cell is much bigger than a typical prokaryote. Its DNA is held inside a separate membrane (forming the cell nucleus) and it has other structures (organelles) inside the cell, too, each with their own function. Eukaryotes probably first evolved when larger prokaryotes engulfed smaller ones. Mitochondria—structures found in eukaryotic cells that generate energy—are very similar to free-living bacteria, since they have their own DNA, which is quite distinct from the cell’s nuclear DNA.

RNA strand

Virion (a single virus particle)

Animals are aware of the difference between life and death, and humans are not the only animals that show grief at the permanent loss of a companion.

Prokaryotic cell

Eukaryotic cell

// How evolution works

Imagine that you are a fennec fox, living in the Sahara Desert. You are a deadly predator—of insects and perhaps the occasional lizard. To find and capture your prey, you need keen senses (those ears aren’t just there for decoration) and stealth. However, you might also be the hunted rather than the hunter. To escape your predators, you need alertness and speed. It will help you out a lot if you have excellent sandy-coloured camouflage, too, and top-notch kidneys to deal with desert life. Your big ears also help you keep cool. If you want to have babies, you have to be fit enough (in both senses of the word) to attract and keep a partner, and you have to be nurturing enough and a good enough provider to take great care of your offspring so that they survive to adulthood. If you have all those attributes in abundance, you will probably live a long life, and leave behind many descendants.

It’s easy to see that an animal that functions very well in its environment will survive longer than one that doesn’t. It’s also easy to see that breeding success is a combination of living long enough to have lots of breeding opportunities and functioning very well in the specific ways involved with breeding. Those that are less well adapted have shorter lives and fewer offspring. This is the process of natural selection, or survival of the fittest.

The fennec fox has a sandy-colored coat to blend in with its desert habitat, and its large ears help it cool down as well as hear every tiny sound.

The idea of natural selection presupposes that all of the animals in a population are at least a little different to one another, in all kinds of ways – and indeed they are. Much of this variation is there from the start of life, and is down to genetic variation. Not only do animals inherit a different combination of genes from their parents, but genes can also spontaneously change (mutate). With natural selection at work on genetic variation, each new generation is the offspring of a non-random sample of the generation before—the progeny of the best.

Surely after many generations of this, though, you will just end up with better fennec foxes? Let’s try, then, a further thought experiment. Let’s take half of our Sahara-evolved fennecs and distribute them in other habitats. Some can go to a snowy mountain and some to a deep rainforest. We will leave them to it for a few hundred millennia, then return. What do we find? The traits that made these animals so well adapted for desert life are no longer advantageous, but other traits have been favored instead. For example, on the mountain, the foxes with the thickest and whitest fur and smaller ears would have survived best, and passed on these traits through the generations. In the forest, a thinner and darker coat is better, and extreme kidney efficiency has become redundant. Meanwhile, the fennecs that stayed in the desert have carried on being well adapted to desert life. We now have three very different and distinct lineages of fennecs—they differ in the way they look, their anatomy and their behavior—and if we reintroduced them they might not even recognize one another as close cousins.

Dark or melanistic morphs of the peppered moth outnumber pale morphs in environments where industrial pollution blackens walls and tree trunks.

Now, stretch out this process for many millions of years, and replace our deliberate meddling (which in reality would probably kill off our subjects before they had a chance to adapt) with slow-paced but very far-reaching changes to the entire planet’s environments. The scene is set for evolution to occur and, over our planet’s lifetime, produce the wonderful and diverse array of living things we see today.

Adaptive radiation: a single tanager species reached the Galapagos islands about 2.3 million years ago, and there, over many generations, it diversified into many different species (the Galapagos finches), with varied bill shapes to eat the different kinds of food available.

// The first animals on Earth

The very earliest indisputable traces of life on our planet date back to 3.5 billion years ago—a billion years after the planet came into being. There are, however, much older fossils that may also indicate the presence of simple life—if so, then bacteria-like organisms already existed when Earth was less than half a billion years old.

For more than half of its existence, Earth only held these very simple, bacteria-like life forms. The first complex single-celled organism appeared just 2 billion years ago, and multicellular life forms have been around for a little over 1.5 billion years. The earliest true animals? They are a mere 900 million or so years old. This is because while all animals are multicellular, not all multicellular organisms are animals.

When we think of an animal, we probably picture a cat, a dog, a horse—something that’s just like us. But we and our fellow mammals make up a tiny fraction of the animal kingdom. Even if we add in all of the other vertebrates—the birds, reptiles, amphibians, and fish—we are still only looking at barely 5 percent of all animal life, and a very recently evolved 5 percent at that. The first kinds of animals on Earth resembled modern-day sea sponges and comb jellies. The former, branching out of the seabed, might have struck us as much more like plants, and the latter, with their strangely amorphous, soft and translucent bodies, look more like drifting blobs of snot than living things; they don’t have distinct body parts like we do, and are akin to colonies of co-operating cells. However, the truth of their animal nature is revealed not in their outward form, but in the anatomy of those cells.

If you have ever looked at plant and animal cells under the microscope, you will know that there are several distinct differences. One of the most obvious is that the plant cells have a rigid cell wall which often gives them a rather geometric shape, while animal cells only have a flexible cell membrane and tend to look round and soft. Fungal cells also have a cell wall. This is a key difference between animals and other multicellular life.

A comb jelly. This simple but successful creature is a modern representative of one of the most ancient animal lineages.

Plants are producers – making their own energy stores by using sunlight. This energy passes up the food chain, via plant-eating primary consumers such as zebras, and on to animal-eating secondary consumers such as lions.

Another important difference between animals and plants is how animals obtain their food. Plants can make glucose out of carbon dioxide and water, through the process of Sun-powered photosynthesis. Animals must consume other organic material. This means that animals cannot exist without