Terrestrial Fauna

the aggregate of animals that inhabit dry land. Terrestrial fauna comprises approximately four-fifths of all of the earth’s animal species. This large number is explained by the greater variety of living conditions on land than in the watery environment, the many sharp changes in the geological history of the land, for example, in climate and relief, and the isolation of continents and islands.

These factors also account for the much higher rates of speciation of animals living on land and for the marked differences between the terrestrial fauna of different regions. At the same time, no forms of coelenterates, echinoderms, sponges, nemertines, brachiopods, Pogonofora, acraniates, tunicates, bryozoans, en-teropneusts, cephalopods, or lamellibranches occur on land. The biomass of terrestrial fauna is approximately 1,000 times smaller (according to some data, 10,000 to 100,000 times smaller) than the terrestrial plant biomass. In contrast, the world ocean’s animal biomass is almost 30 times larger than its plant biomass.

Since air is much less dense than water, land animals usually have a strong internal or external skeleton. Those lacking a skeleton, such as worms and slugs, possess a flexible body. Insufficient humidity in the air resulted in the development of a thick integument to prevent the evaporation of body moisture, especially in insects, reptiles, birds, and mammals. Some animals, such as mollusks, are protected against evaporation by a layer of mucus that covers the body. In others, the respiratory organs (lungs and tracheae), which are most subject to drying, are situated inside the body. The thick eggshells of terrestrial animals are another example of adaptation to an insufficiency of moisture in the air. Some animals are capable of storing moisture.

A rapid metabolic rate is characteristic of terrestrial animals because there is more oxygen in air than in water (207 cu cm in 1 liter of air compared to 7 cu cm in 1 liter of water). Most land animals are highly mobile, as they need to fly, run, or jump in order to search for food. There are very few sedentary animals on land, the insect suborder Coccoidea being an exception. As a result of the sharp temperature contrasts on land, birds and mammals developed a constant body temperature (warm-bloodedness). The groups of animals that are taxonomically most highly organized—insects among invertebrates and mammals and birds among vertebrates—originated on land.