The evolution of horseshoe about 65 million years ago, an asteroid with a diameter of 10 km broke into the earth's orbit, causing natural disasters such as tsunami, earthquake and volcanic eruption, which led to the extinction of dinosaurs. However, mammals have a wide range of energy sources because of their insectivorous and omnivorous nature. Coupled with their small size and small demand for energy, mammals survived the extinction and gradually flourished.
Due to the extinction of dinosaurs, most of the earth's ecological niches were vacated, and mammals began to fill the void. Among them, not only carnivores but also herbivores appeared, and the ancestors of Chiroptera were one of them.
During the Paleocene-Eocene, the temperature of the earth soared in a short time because the carbon dioxide content of the earth reached a critical value. The high temperature climate makes the earth's water source evaporate a lot, and then it falls to the earth in the form of rain. In this hot and rainy weather, the forest is gradually flourishing. Even the polar regions have no permanent glaciers, but a large rainforest.
For the ancestors of Chiroptera, the plants in the rain forest are tender and juicy, and the staggered forest trees can provide them with better shelter, and the Chiroptera gradually flourished.
However, the earth's environment is not static, and a catastrophe is coming. For some reason, the earth suddenly cooled down, which caused the original ocean current to be broken, the earth's rainfall decreased, and the air became much drier.
Many forest vegetation is no longer suitable for growth. Instead, grass plants have flourished. Maybe for us, whether it is leaves or grass, it is a plant. For Chiroptera, what plants to eat is not to eat, and the prosperity of grass can also satisfy the survival of Chiroptera.
But this is not the case. Herbs are relatively low, and a lot of sand and gravel are mixed. In addition, the leaves of herbs are hard, which makes it difficult for Chiroptera to adapt to this change, so a large number of Chiroptera became extinct during this period.
In order to adapt to this environment, the surviving Chiroptera evolved high crown teeth, that is, the teeth are super long enough to wear for a lifetime. In addition, because there is no shelter in the grassland, carnivores can easily find them. In order to avoid predators, some Chiroptera began to evolve hooves, while horses are more extreme. They only have one middle finger, and the middle finger evolved hooves, while other toes degenerated. This way of walking greatly improved the horse's grip on the ground and made it run faster.
Because a horse has only one horseshoe, humans can install horseshoes on its horseshoes, but it will not affect their walking. Horses' hooves are equivalent to human nails, and they will grow with the growth of horses. The reason why human beings install horseshoes for horses is that after human beings domesticate horses, they need to rely on them to carry heavy objects and act as means of transportation.
Because the horse consigns heavy objects for a long time, the horseshoe is seriously worn. If the horseshoe is not revised for the horse, when the horseshoe is worn to the horse's foot, the horse will be unable to walk because of eating pain, which will delay the progress of human beings.
Why don't cows nail their paws? Cows are herbivores like horses, but they are far related. They belong to Artiodactyla and have even toes.
The evolution path of cattle is different from that of horses, and the main difference is their hooves. Cattle have multiple hooves, so they are called Artiodactyla, while horses have only one hoof, so they belong to Artiodactyla.
The two hooves of a cow can be separated from each other or gathered together when walking, so it is difficult for people to install the hooves for them.
Moreover, cattle are mainly used for farming in our country, rather than carrying heavy objects, so the hoof of cattle wears slowly, and even if the hoof is not installed, it will not cause serious harm to cattle.
At present, in many places, the way cattle cultivate the land has been abolished and they are cultivated by machines instead, so the burden on cattle becomes less. Nowadays, people raise cattle not for cultivation, but for meat quality and milk, so cattle don't need to nail their feet to protect them.
In fact, some horses used for breeding don't nail horseshoes either. This is because horses used for breeding hardly participate in transportation and manned work, but are kept in stables. They don't have much daily walking and consumption of horseshoes, so these horses don't nail horseshoes. But sometimes the horseshoe will grow too long and affect walking if it is not repaired for a long time.