What were the First Animals to Walk on Land?

Terrestrial animals refer to animals that live on land, and most of them breathe air. Among the underground animals, some tiny animals that live by breathing dissolved oxygen in pore water are also terrestrial animals. Terrestrial animals breathe air in order to adapt to terrestrial life, prevent evaporation of water in the body, support the movement of the body, protect eggs and larvae, and the final product of nitrogen metabolism is not excreted as ammonia nitrogen but as urea and uric acid nitrogen.

Terrestrial animals are animals that live on land. Terrestrial animals live in a relatively dry environment, and their skin evaporation, breathing and excretion may cause the body to lose water. In order to ensure the water balance in the body and the normal metabolic activities of the cells, the terrestrial animal's shape, body color, growth and development , Behavior and ecological distribution are adapted to land life. For example, animals living in dry and cold areas have lighter body colors, while animals living in humid areas have darker body colors. Terrestrial animals must also adapt to significant changes in temperature on the land. Body temperature regulation and temperature tolerance are key factors for the animal's ability to survive on land. Terrestrial animals have two types of temperature: constant temperature and constant temperature. The body temperature of temperature-changing animals is mainly maintained and regulated by external heat sources such as the sun. Their body temperature changes with changes in the external environmental temperature. When the temperature drops or rises to the limit where they cannot adapt, these animals begin to dormant. . There is also a large category of terrestrial animals-isothermal animals. They rely on efficient metabolism in the body to generate heat and their own special thermal insulation structure to maintain body temperature. These animals are not as dependent on the environment as warming animals. They can move freely during the day, night, cold and summer, and have a strong survival competitiveness. They can continuously adapt to new living environments and have a wide range of life and distribution. ^[1]

Ancient animals have spent their "infancy" in the cradle of the ocean, and some of them will come later; to leave this cradle and look for a new world, it is the land they have never set foot on.

The earliest landed animals were the ancient scorpions and spiders, both of which were arthropods. In the Cambrian shallow seas, the most typical arthropods were trilobites, and the ancient scorpions and trilobites were close relatives. They may have been advanced from a common primitive ancestor at the earliest.

The landing of arthropods was not accidental. From the late Silurian to Devonian, due to the orogenic movement caused by crustal compression, the land rose from the ocean floor in large areas, the water surface area was reduced, the climate became dry, and Arthropods are often in shoals or quagmire. In order to adapt to this environment, they began to differentiate the trachea for breathing, and used appendages and segmented bodies to jump or crawl on the dry mud ground. Gradually, their gills degenerate, and they change into a terrestrial animal.

Since then, more and more animals have been able to survive on the land, and land has gradually become the second home of the animals. In this process, the landing of vertebrates is of great significance, because they will evolve into terrestrial intelligent life like humans in the future. ^[2]

The body structure of terrestrial animals has many characteristics, and they can all be explained from the basic laws of mechanics. In fact, this law is: the working ability of animals' limbs is proportional to the cube of their length; the work consumed to control their limbs is proportional to the cube of their length. Therefore, the larger the animal's body, the shorter their limbs, wings, and antennae. In all terrestrial animals, the smaller the animal, the longer the limbs. For example, the blind spider we are all very familiar with is a good example. If the animal's body size is very small, their shape will be similar to that of a blind spider. These phenomena can be explained by the laws of mechanics. However, if their bodies reach a certain size (for example, a fox), their bodies are no longer similar. This is because their feet cannot support the body's weight, and this makes their movement very inconvenient. However, in the ocean, the weight of animals can be balanced by the repellent effect of water, so their shapes may also grow into the shape of blind spiders. For example, deep-water crabs, which are only about half a meter long, but have long legs 3 meters. ^[3]

The most basic feature of animals is that they can move freely. Generally, animals can walk from one place to another freely, but plants cannot. This is one of the differences between animals and plants. Animals move around to get food and find a place to live, freeing them from predators. Different types of animals have different movement parts of their bodies. Most terrestrial animals are as small as bugs and spiders, as large as reptiles and mammals that move on their legs; monkeys and sloths are Rely on the assistance of the upper limbs to climb to the tree; the snail glides on the secretions of the abdomen; the snake advances through the twist of the entire body. Muscles play a very important role in animals during exercise. The muscles of vertebrates are closely linked with their bones, allowing animals to crawl, walk, fly or swim.

Animals such as antelopes, gazelles, and zebras that live in vast environments like grasslands are extremely important because they are closely related to their lives. Only extremely fast can make them free from predators such as cheetahs, lions and wild dogs, and will not become their prey. The muscles of these animals are mainly concentrated on the thighs and body, and their calves and feet are relatively light, which can effectively coordinate reciprocating movements. ^[4]

Mammals

Mammal Mammal is a thermostat, vertebrate, with hair on the body, most of which are viviparous, and feed offspring through the breast.

Terrestrial animal

Birds are usually feathered and ovum-like animals with high metabolism rates and long bones are mostly hollow, so most birds can fly. The earliest birds appeared about 150 million years ago. Their bodies are spindle-shaped, their forelimbs are specialized in wings, their bodies are feathered, their body temperature is constant, their muscles and chests are developed, their bones are healed, thin, hollow, and their brains are more developed. Airbags allow double breathing, without a bladder and a short rectum can reduce body mass. These physical characteristics are all adapted to flying.

birds

Terrestrial animal reptile

Reptiles are more adaptable to land life than their amphibians. The body is clearly divided into head, neck, torso, limbs and tail. The neck is more developed, can be flexibly rotated, increases the predation ability, and can give full play to the functions of sensory organs such as the head and eyes. The well-developed bones provide the conditions to support the body, protect the internal organs, and enhance athletic ability. Breathing with lungs, the heart consists of two auricles and incompletely separated ventricles, and gradually evolves in a direction that separates arterial blood from venous blood. The brain structure has been further developed than amphibians, and the sense organs have also increased complexity and enhanced functions.

Terrestrial animal amphibians

Amphibians are the most primitive terrestrial vertebrates. They have both new traits adapted to terrestrial life and traits adapted to aquatic life inherited from fish ancestors. Most amphibians need to lay eggs in water. There is a metamorphosis during development. Juveniles () are close to fish. Adults can live on land. After hatching, the metamorphosis is almost completed, and some larvae are maintained for life. Amphibians first appeared in the late Devonian period of the Paleozoic. The earliest amphibians had labyrinths, which are called labyrinths. In the Carboniferous period, there were also shell vertebrae with no labyrinth. The Permian was very prosperous, this era is also known as the era of amphibians. At the end of the Permian, all the crustaceans were extinct, and only a few of the dentate species continued to survive for a period of time in the Mesozoic. After entering the Mesozoic era, modern types of amphibians appeared. Their skin is bare and smooth, and they are called slippery amphibians.