The largest dinosaurs in the world are four stories tall. How did they grow into such giants?

Although life has been on land for more than 400 million years, there have been no animals longer than 20 meters except for the large sauropod dinosaurs. So how did the sauropod dinosaurs grow so big? How much did they eat a day? How did they support such a huge body, and how did the various organs in their bodies coordinate?

How big is the largest dinosaur

There are many competitors for this throne, including Barosaurus, Supersaurus, Patagoniasaurus, Diplodocus, etc. However, the largest dinosaur recognized by paleontologists is Argentinosaurus. Its body length reaches 38 meters, which is equivalent to the length of three buses connected end to end, and its height is 10 meters, which is close to the height of a four-story building. The weight of this "giant" is also quite amazing, estimated to be between 60-90 tons, which is more than the total weight of ten elephants. The giant Ruyangosaurus discovered in Henan, my country, some experts speculate that its body length can reach 38.1 meters after the bones are restored, and it should also be a strong competitor for the world's largest dragon.

The largest terrestrial mammal that has ever appeared in history, the Paraceratherium, was more than 8 meters long and weighed 22 tons, less than one-third of the size of the Argentinosaurus. With its body size, it was just a small follower in front of the Argentinosaurus.

Some people believe that the oxygen content in the Mesozoic Era when dinosaurs lived was much higher than it is now, the climate was warm, the plants were lush, and there was food everywhere, so sauropods could grow so huge. Is this really the case? According to the latest research, the average atmospheric oxygen content in the Jurassic and Cretaceous periods was lower than the current 21%. The energy value of ferns, the staple food of sauropods, is not much different from that of today's herbs. In the Cenozoic Era when mammals flourished, there was no shortage of warm climates and lush plants, but no species appeared that could challenge the king status of sauropods in size. Therefore, the amount of atmospheric oxygen and the abundance of food may not be the main reason why dinosaurs became larger.

Then we need to change our thinking and look for the answer from the research object itself. Fortunately, this question is not only of interest to ordinary people like us, but also attracts the attention of dinosaur experts. Professor Martin Sander, a famous German paleontologist, launched an 11-year research project on the gigantism of dinosaurs, and answered the following questions about why sauropod dinosaurs could become giants.

What did you rely on to grow so big?

What everyone is most concerned about is how sauropod dinosaurs carried their huge bodies that were as heavy as a mountain.

First of all, the soles of sauropod dinosaurs are very wide. When they walk, they can distribute their huge body weight to the four soles, reducing the pressure on the ground and preventing themselves from getting stuck.

Secondly, although sauropods were huge, their bone walls were thin and hollow with many holes, which greatly reduced the weight of the bones. Most sauropods had air sacs similar to birds, which surrounded the spine and even filled the gaps in the limb bones, reducing the pressure on the whole body. In a sense, large sauropods were not a solid mountain of meat, but hollow and inflated.

Research has found that sauropod teeth are worn only on one side, which means they swallowed the plants directly after peeling them off, without chewing them at all. This way of eating can save chewing time, eat quickly and continuously, and greatly increase the amount of food eaten per unit time.

The restored picture of Argentinosaurus, the picture comes from Tuchong.com

Today's herbivores such as cattle and horses have well-developed chewing abilities, which indeed improve the efficiency of food utilization, but limit the efficiency of eating, and therefore also limit the continued growth in body size.

Another advantage of sauropods in feeding is that their necks, which are half their body length, are like an extra-long feeding pole that can sweep across a large area of ​​plants with just a swing. This allows them to feed over a large area with just a short movement, saving energy during long feeding periods.

With the help of these two weapons, an adult Argentinosaurus can eat more than 500 kilograms of plants every day, making it a plant "vacuum cleaner" of the Mesozoic era.

Paleontologists have found gastroliths in sauropod dinosaur fossils, and speculated that they might have used gastroliths to grind food into powder before digestion through the peristalsis of the stomach, just like today's chickens, ducks and other animals, which eat small stones to help digestion.

More importantly, the reason why sauropods have huge stomachs is that they have an extended gastrointestinal tract that helps them store and digest large amounts of plants for a long time. These intestines house some bacteria that can decompose plants, forming a special structure similar to a "fermentation tank" to help digest huge amounts of plants. However, the gas produced by the decomposition of a large amount of plants also turns sauropods into walking methane tanks, so paleontologists joked: "If you travel back to the Mesozoic era, you must not walk behind sauropods, because these dinosaurs must fart frequently."

Sauropods have a unique air intake system. Their huge bodies consume a lot of oxygen all the time, so they need an efficient respiratory system. In addition to strong lungs, the respiratory system of sauropods also has the previously mentioned air sacs that are spread all over the body like birds. These air sacs are connected to the lungs and are divided into two parts, front and back. Whether inhaling or exhaling, there is always fresh air flowing in the lungs, which greatly improves the efficiency of gas exchange and increases the absorption of oxygen. Therefore, in the Mesozoic Era, when the oxygen content was even lower than today, sauropods were able to rely on them to obtain more oxygen to meet their own survival needs.

Sauropod dinosaurs could also rely on their air sac structure to speed up air flow to dissipate heat, thus preventing functional disorders or even death caused by excessive body temperature.

The huge body of sauropods requires a powerful heart to supply blood to the body. Its four-chamber heart is not only strong and powerful, but also has undergone structural enhancements such as thickening of blood vessel walls and strengthening of muscular venous pumps during the evolution process, ensuring blood circulation throughout the huge body.

Efficient growth and reproduction strategies

Although sauropods were huge, they were very small when they were born, less than 1 meter long and weighing only 5 kilograms. In order to grow up faster, young sauropods had a high basal metabolic rate and maintained an amazing growth rate of 1 ton per year.

When sauropods reach adulthood, their basal metabolic rate changes from high to low, entering a low energy consumption state. However, after adulthood, sauropods will continue to grow slowly until death, so the older they get, the bigger they get! Mammals basically stop growing after adulthood, and their body size does not change with age.

Sauropod dinosaurs did not build nests and raise offspring, but laid multiple eggs at a time like turtles, winning by numbers, so their breeding costs were lower. This also reduced energy consumption, allowing them to concentrate on growing up.

Of course, the reasons why sauropods could grow so large are obviously not just the ones mentioned above. Many reasons are both the driving force and the limitation of dinosaurs' large size. When sauropods break through these limitations, they will step by step impact the peak of the largest land animals, and finally win the crown of the king of land!

This article is a work supported by Science Popularization China Starry Sky Project

Author: Liu Sen

Reviewer: Wang Yuan (Director of the Paleozoological Museum)

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.