□ Xu Jing (special feature of China Daily)
Why on earth did dinosaurs disappear from the earth? The scientific community has been debating this for a long time. According to western media reports on April 20th, British scientists put forward a new speculation that if the physiological structure of dinosaurs was similar to that of today's reptiles, then 65 million years ago, due to the great changes in the earth's environment, the sex of dinosaur offspring was greatly affected by temperature, resulting in serious gender problems.
Serious gender imbalance, fewer and fewer female dinosaurs, so that the dinosaur family gradually can not continue to reproduce.
The earth's climate became cold, and the dinosaur family only added males.
In the animal kingdom, the sex of vertebrates is determined by the chromosomes of both parents at the moment of fertilization. If an X chromosome meets a Y chromosome, then the next generation is male. If two X chromosomes meet, the next generation will be female. This is how the sex of lizard offspring in mammals, birds, snakes and reptiles is determined. However, due to the differences in physiological structure and metabolism, most oviparous reptiles have a unique way to determine the sex of their offspring. They are affected by the temperature of their nests during the incubation process, and turtles and crocodiles are typical examples. Even if they lay two layers of eggs in the same nest, the sex of the hatched larvae is different due to different temperatures.
In recent years, Professor david miller from the University of Leeds led a research team to conduct related research. They think that the physiological structure of dinosaurs is very similar to that of today's egg-laying reptiles. They infer that the sex of dinosaur offspring is likely to change with the change of temperature, and suggest that cold weather conditions will lead to more male babies in dinosaur families, which is likely to be an important reason for the extinction of dinosaurs.
Asteroids hit the earth, gender imbalance, and eventually extinction.
At present, there is a unified view in the scientific community: 65 million years ago, an asteroid collided with the earth, causing many dinosaurs and other ancient creatures to die. The collision caused a lot of dust to fly all over the sky, and volcanic activity became more frequent, which led to the increase of volcanic ash in the atmosphere. As a result, the earth was once overcast and there was little sunshine, and the temperature of the earth dropped sharply.
Miller believes that the surviving dinosaurs continue to survive and reproduce under such conditions. However, due to the cold weather, most of the young dinosaurs hatched by dinosaur mothers are male, which makes the male-female ratio in the dinosaur world seriously unbalanced. With the gradual decrease of female dinosaurs, the dinosaur family also went extinct.
Sherman Silbo, another expert of Miller's research team, also said: "65 million years ago, life on earth did not completely die out. At that time, the temperature changed a lot, but the genetic system of those giants (dinosaurs) did not change, so they could not adapt to the environment, and even the dinosaur family lost its balance. "
It has been pointed out that turtles and crocodiles appeared on the earth long before asteroids hit the earth. How did they escape this disaster and successfully multiply to the present? Recently, experts have also explained this. Some scientists wrote in the paper: "These animals (turtles and crocodiles) have been living in the land-water border areas, such as river beds and shallow water pits, where the environmental changes are relatively small, so they have more time to adapt to the environmental changes."
The previous dinosaur extinction theory
Scientists who hold this view believe that the orogeny in the late Cretaceous caused drastic changes in the climate, many plants died, and dinosaurs who ate plants also died.
■ "Disease Theory" American authoritative pathologists believe that when the dinosaur species reached its peak on the earth, a mysterious virus or plague similar to AIDS currently faced by human beings suddenly swept the whole earth, making the species that dominated the earth/kloc-0.4 billion years extinct.
■ "Geomagnetic motion theory" was put forward by scholars represented by Kenny College in the United States. The earth's magnetic pole and polar circle moved many times, and each movement led to great changes in the natural environment, and dinosaurs were doomed to extinction.
■ "Constipation Theory" People who hold this view believe that the food of herbivorous dinosaurs was mainly cycads, ferns and other plants. Later, these plants became extinct, and dinosaurs had to eat mulberry and other plants, causing constipation and death.
■ "Racial aging theory and mammalian competition theory" Those who hold these two views believe that in the competition for survival, "latecomers" mammals not only compete with dinosaurs for food, but also eat up dinosaur eggs and make dinosaurs extinct.