While there are many types of animals we could create, some are more likely candidates than others. To get started, knowing how they’re classified might give us ideas.
Animals are either invertebrates or vertebrates; i.e., spineless or not. The distinction has no other significance.
Invertebrates, which make up 97% of animals, include worms, sea urchins, jellyfish, snails, arachnids (spiders, scorpions), crustaceans (lobster, crab), corals, and insects. On Earth, they tend to be smaller than vertebrates, but Jabba the Hutt from Star Wars was a huge worm, and the giant spider from The Lord of the Rings is infamous. Our characters are unlikely to use invertebrates for domestication, sport, guards, or transportation unless we make them enormous, so our use of them is limited, but they can be food, pets, and used for materials. These purposes will be discussed in the next section. Swarms of such small animals, like insects, can pose a problem, and we can invent a swarm that takes place at given intervals (as with cicada) that people prepare for, for example. Imagine that with giant insects.
Vertebrates include the animals you probably thought of when starting this chapter: amphibians, birds, fish, mammals, and reptiles.
Amphibians include frogs, toads, and salamanders, and require water to breed, laying larva that metamorphose into the adult form. They are capable of living on land or underwater but need moist habitats to keep their skin damp. They can acquire air through their skins to assist their lungs, with a few having no lungs at all; this allows them to remain submerged indefinitely. They are typically small but one extinct species on Earth was up to thirty feet. Being cold-blooded, they rely on environment to regulate body temperature and have slow metabolism, meaning they require less food and expend less energy. Their tongues are muscular and can often protrude surprisingly far, being coiled up when not in use.
Some species have skin glands that secrete poison, whereas some secretions just make them taste bad so they’ll be spit out instead of consumed. Some are lethal to humanoids and this is a good reason to invent some amphibians for our world, for use as poisons. The poisonous ones are often brightly colored as a warning and are more likely to actively search for prey, their appearance warning away predators. The camouflaging amphibians ambush prey.
Frogs can be venomous, too. The difference between venom and poison isn’t well understood by lay people, but venom must be injected into the body. This typically means being stung, bitten, or stabbed. By contrast, poisonous animals can merely be touched and are relatively passive. Venom is typically for both offense and defense while poison is for defense.
Frogs and toads appear similar except the former has smooth skin and the latter warty; both have no tail, long folding legs, and big eyes. Salamanders look more like lizards, being low, flat, and possessing a tail. All have four legs, webbed toes, and no claws. Frogs and toads have excellent hearing. They periodically shed skin in one piece and sometimes eat it (yummy).
Virtually all amphibians are predators who hunt by sight and swallow prey whole, dining on small, slow moving insects and only chewing a little to subdue their meal. Holding still is how potential victims avoid being detected and eaten, but some amphibians hunt by smell and may be able to locate prey that doesn’t have a scent, even in the dark or when it’s not moving. Many amphibians are nocturnal and hide during the day.
While they are seldom seen (unless you invent large ones), amphibians are heard quite often during mating season, but their calls are fatiguing to themselves and could draw predators, in addition to attracting females. A deeper voice typically means a bigger amphibian. Frogs can actually scream when attacked and their vocalization can be aggressive to ward off competition. Some amphibians are territorial about sites for breeding, shelter, or food, and physically attack if necessary. Like reptiles, some salamanders can detach their tail if a predator has them by the tail, and regrow it.
There’s a tendency to overlook birds during world building and storytelling, probably because they have limited use to us except as food or symbols (like associating a dove with peace). Birds consume food smaller than them, so unless we have giant birds, they’ll be keeping clear of our species unless they’ve been domesticated and used like carrier pigeons, for example, or as pets, as in the parrot. Birds of prey like hawks can be used as hunters, possibly bringing our adventurers small game like rabbits or fish for dinner. Bird eggs are among the more useful aspects, but then what’s different about our bird’s eggs that we can’t get from a run of the mill chicken, for example?
As with all animals, when deciding to invent a bird, consider our purpose and those of our characters. We may find there’s little reason to invent one that isn’t an analogue; we can just combine aspects of different birds, like plumage, behavior, trainability, and prevalence, and slap a different name on them and be good to go.
Migration is one of the characteristics of a world that might be more worthwhile to consider. Not all birds migrate, but land birds can migrate 1600 miles and shorebirds up to 2500 miles, with the longest distance for one species being 6300 miles. Some species don’t necessarily return the next year, based on food availability (if that’s the driving force behind migration, as breeding is the other big motive). It isn’t just the carrier pigeon that can return to a specific place, as most birds can navigate incredible distances and return home.
Some species flock for safety in numbers, especially in forests where predators are harder to detect, and more eyes offer more chances to warn each other. Some birds also cooperate with other animals, such as sea-diving birds that take advantage of bait balls of fish; this happens when animals like dolphins herd small fish to the surface for themselves to eat, helping out the birds, too.
For general characteristics we might not be familiar with, most birds are diurnal but some operate at night, during twilight, or when tides are appropriate for feeding if they’re a bird that wades in coastal waters. Some birds are more intelligent than most other animals, which could be interesting when combined with ferocity and large size. In contrast to reptiles and amphibians, birds rapidly digest food so they can fly again; they have no teeth and swallow most things whole. On isolated islands, birds may become flightless due to a lack of predators.
Not all birds create a nest for eggs but generally hide them from predators if so. Incubation is from ten to eighty days and in many species is only once a year, with from one to nearly a dozen eggs. This is useful to know if we’re using enormous birds as in The Lord of the Rings because there would theoretically be a demand for such huge eggs.