Everyone who has seen the "List of Fengshen Gods" or "Fengshen Yanyi" knows that there is a person named Tu Xingsun in it, he will "escape the earth" He can drill into the ground to hide, in the land and the ground horizontal, vertical three-dimensional space free shuttle, he wants to sneak attack who is invincible, to escape is even easier.
Of course, Tu Xingsun is a character in mythological novels, but in the natural world, animals that will "escape" or live underground, such as low-level ants, earthworms, centipedes and other invertebrate soil animals, higher such as mongooses, moles, armadillos and other vertebrates, take the mammal mole, its eyes and ears are small, hidden in thick hair. As a result of living underground, their vision and hearing are severely degraded. However, their sense of smell and touch is very sensitive and can perceive the environment in the dark.
In addition to this, they are very resistant to low oxygen. This is also an important reason why they can live underground. Their bodies resemble a cylinder, and their two forefoots are wide and flat, like two large shovels, with great strength. Moving forward in the dirt, it is all up to these two "big shovels" to open the way. When they travel underground, they are like swimming in the water, and the two forefoots alternate, pulling the soil to the sides of the body. What is this strange digger digging and digging every day? Of course, I'm looking for something to eat! What do moles eat? Earthworms, tide worms, and all kinds of worms are all delicious in their eyes. Occasionally, they will also eat a little vegetarian and taste the roots of the plant. Moles have a quick metabolism and are always hungry, so they spend their days looking for something to eat.
In fact, mammals that mastered the art of earth or lived underground existed in large numbers as early as the Mesozoic Era. When we talk about the Mesozoic Era of mammalian origins, nature's first impression is the age of the dinosaurs. Then relatively weak mammals, under the pressure of giant predators such as dinosaurs, naturally want to find some ways to expand the ecological niche and improve the possibility of survival. In recent years, the explosion of Fossil Discoveries of Mesozoic Mammals centered on Western Liaoning has made us realize that mammals, even in the shadow of dinosaurs, have evolved adaptations to a variety of living environments such as the sky, land, rivers, forests, especially underground nests.
On April 7, 2021, Mao Fangyuan and Zhang Chi, associate researchers of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, in collaboration with Meng Jin, researcher of the American Museum of Natural History, discovered two new fossils of new mammal genera in the Early Cretaceous (about 130 million to 110 million years ago) strata of the Rehe Biota in Northeast China, the Chinese digger and the Chen's digger, which are the first fore-clawed excavator-type burrowing mammals found in the Rehe biota.
Fossil specimens of Chinese diggers and Chen's carapaceans
Restoration map of the main mammals of the Rehe biota (zhao Chuang painting)
As mentioned earlier, the less competitive pressure faced by burrowers does diminish a lot compared to ground-dwelling mammals. From the existing research, there are not many species that have evolved and developed cave habits in non-inferior reptiles, such as Oryctodromeus cubicularis in the early chalk in southeastern Montana, and Changmiania liaoningensis in the early chalk of western Liaoning in China, all of which are small plant-eating dinosaurs. Some common burrowing lizards and turtles and turtles do not pose much of an ecological threat to mammals. Compared to the dinosaur-rich ground, life underground seems to be less crowded in terms of habitat stress. Some of the small plant-eating reptiles of the lower pores that are closest to mammals are also common in their burrowing habits.
Niches are not crowded, meaning that food is relatively easy to obtain, as most early mammals were considered insectivores or omnivorous. Then in the underground environment, there are sufficient resources of insects (insects, worms, flatworms, etc.) and their larvae and eggs, plant rhizomes, fungi and other resources to provide energy for cave dwellers.
Cave dwellers generally have multiple tunnels and turns, which can effectively avoid predators in this environment, and some large predators are difficult to enter, posing a threat to cavers. Caves can also shelter from the wind and rain, maintain relatively constant temperature and humidity, store food, protect cubs, and even shelter from extreme weather and events. Therefore, it is not embarrassing to use your feet to cut out a few rooms and halls, and even life is quite comfortable.
Of course, the most common should be the semi-burrowing mammal type, only when you need to rest or encounter danger, return to a safe and warm and quiet cave, but foraging activities still choose to be on the ground with more resources, such as some common voles, gerbils, weasels, groundhogs, hares, foxes, coyotes, badgers, anteaters, aardranths, armadillos, wombats, kangaroos, etc., and even early humans, have maintained a semi-burrowing habit.
In addition to the recent discoveries of Chinese diggers and Chen's cerapids, mammals with semi-burrowing habits already existed in the Mesozoic Era, such as the Akidolestes of the early Cretaceous River biota and the Repenomamus of the early Cretaceous Tricus that could prey on small dinosaurs, all of which, according to morphological statistics, had semi-burrowing habits. It can be seen that even predators still need to balance the series of problems of resource access, energy maintenance and life safety, and cave dwellers undoubtedly have relative advantages.
And those who are purely cave dwellers such as moles, hoofed rabbits, mole-shaped rats, etc. (mainly for tubetooth, poor tooth, rodent), because of adapting to the full dark cave life, vision degradation is serious; hearing is mainly low frequency, to adapt to the spread of sound in solid media such as soil; but other sensory organs are more sensitive, such as smell and touch, to accurately perceive and detect food; because of cave life, their movement speed is slower, the metabolic rate is low; some spines will also grow to expand the flexibility and ductility of the body. Adapt to narrow tunnels and turns; the tail will also become shorter, reducing drag; and it will also evolve tools that are conducive to digging soil.
At present, mammals with burrowing underground life have been found in fossils in western Liaoning, China, such as the Chinese digger (Fossiomanus) and the mininghorn (Jueconodon) of the Rehe biota in western Liaoning, and the late Jurassic digging columnar tooth (Docofossor). In North America, such as the Fruitafossor in the Late Chalk of Colorado, North America, these animals have developed biological characteristics to cope with underground life.
Ecological Restoration of Chinese Diggers and Chen's Sharp Toothed Beasts (Zhao Chuang-eel)
To roost, nature will climb trees; to enter the river, it is bound to paddle; if you want to walk on the ground, you must be able to plane holes. But with so many types of excavation, the tools that everyone uses to plan holes are not the same. The tools that have evolved are mainly divided into the following three categories:
Forelimb excavation. The limbs of these classes are short and powerful, with broad palms and long, strong claws. It has strong flexor and extensor muscles, which provide strong impetus for planing and digging behaviors, such as living mole rats and badgers, Chinese diggers and sharp toothed beasts of the Rehe biota, and excavators of the late Jurassic Yanliao biota.
Tooth excavation. These are mostly rodents, such as voles, gophers, naked mole rats, etc., with a pair of strong front teeth, strong masseter muscles, hard tooth enamel and lifelong continuous growth of incisors, can assist in the use of incisors to gnaw, shovel, dig out the channels that adapt to their survival.
Head assist digging. In addition to digging directly with forelimbs and teeth, some animals have strong, triangular skulls to assist in digging holes. These types of skulls are thickened, nasal bones develop, and the occipital, neck, and shoulders are thick to support the skull. Similar structures are found in the carnivorous golden retriever and the Mesozoic thizophores.
Fossils of The Chen's Sharp Toothed Beasts
Of course, there are some mammalian phylums that adapt to underground life, and there are some extremely special body designs. For example, the hemoglobin of moles contains special hemoglobin, which enables moles to live in a low-oxygen, high-carbon dioxide environment. The hammer bone of the desert mole is extremely enlarged, collecting low-frequency sound localization and replacing degenerative vision. Naked mole rats have evolved cold-blooded or warming properties, unlike mammalian constant temperatures, to conserve energy in the conditions of constant underground temperatures. Of course, these special changes have not yet found evidence in the Mesozoic fossil phyla, but in any case, the Mammals of the Mesozoic Era have been able to make full use of the resources and ecological environment underground and obtain a higher survival rate, which has continued to this day.