Why was everything bigger in prehistoric times
Why dinosaurs could get so big : Big, bigger, gigantic
Without moving its body, a giant dinosaur bends its neck a little to one side and tears off a clump of greenery. It measures 40 meters from the tip of its tail to its snout. The evolution researcher Martin Sander from the University of Bonn works between the front legs of the replica skeleton like an ant between the legs of a dog. Sander has two questions: Why did the dinosaurs get so big millions of years ago? And why are animals living on land today already reaching the end of gigantism at a tenth of the dinosaur dimensions with the African elephant? John Grady from the University of New Mexico in Albuquerque and his colleagues in the journal “Science” now provide a small part of the answers: The metabolism of the dinosaurs ran at relatively high speeds, so they could grow quickly.
Dino metabolism lies between reptiles and birds
In order to be able to assess the metabolism of the giants, the researchers compared how quickly 381 animal species - lizards and snakes, monkeys and other mammals, birds, but also extinct crocodiles and dinosaurs - grow from birth until they reach their maximum size . In this scale, the dinosaurs landed between reptiles, whose metabolism is slow, and birds and mammals, whose organism runs at high speeds.
Today's reptiles need much less food than a similarly sized mammal. On the other hand, animals with a faster metabolism have more energy available and can grow faster. The conclusion is therefore that the organism of the dinosaurs once ran at higher speeds than that of today's reptiles. Snakes and lizards would take longer to reach giant shapes. At this time they would be easy prey for robbers; hence they are modest with smaller bodies. Eva Maria Griebeler from the University of Mainz came to a similar conclusion in the magazine “Plos”. She works in a DFG-funded group that researches the gigantism of dinosaurs.
"Both results contradict other analyzes, which come to a significantly faster metabolism for dinosaurs," says Sander, who coordinates the group. In order to resolve the contradiction, one has to take a closer look at mammals and birds. After all, animals can not only put the additional energy from a faster metabolism into their own growth. Mammals and birds also take great care of their offspring. In doing so, they give them an energy package on the way that improves their chances of survival.
Eat 18 hours a day
It was completely different with the dinosaurs. "A 40-ton mother laid rather small eggs from which a young dinosaur weighing just three kilograms hatched," says Sander. And she produced several clutches each year, with a total of a few hundred eggs. If a natural disaster killed many dinosaurs in a region, they still did not die out immediately. A few adult animals were enough to fill the ranks again. Each animal also had a lot of food available and it could get bigger. A three-ton elephant cow, on the other hand, gives birth to a baby weighing around one hundred kilos - and puts a lot of energy into the 22-month gestation period.
In order to let its huge organism run at full speed, an elephant spends 18 hours a day eating. And it has another disadvantage compared to the dinosaurs: it chews its food so that it can digest it better. The dinosaurs simply ate them down, with their gigantic body the chewing surfaces would never have been large enough and the food intake would have been too slow.
Long neck saves movement
Birds also refrain from chewing. However, they use their high metabolic rate to fly and not to grow. "In order to be able to soar in the air, birds have completely different lungs than mammals," says Sander. So they take in oxygen even when they exhale. On top of that, they have a lightweight skeleton with honeycomb cavities in the bones. There bulges of the lungs grow into it, which can take in more air with each breath. Some birds, such as swans, use this advantage for a long neck, thereby increasing their range. It was similar with the largest dinosaurs, the sauropods. Due to their extremely long necks, they did not have to move much when eating, they saved energy and thus had a fifth property that was important for the giant body. “These animals were a lesson in how evolution works,” says Sander.
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