[Animals] Why aren't there so many giant animals anymore?

[#Wittels-]

Dinosaur Bones Don't Lie: Animals Used To Be Bigger Many Years Ago

Ever since scientists unearthed the first known cache of dinosaur bones in the 19th century, researchers have come up with ideas to explain why giants were common millions of years ago, but less so today (REUTERS)

 

Prehistoric giants used to po[CENSORED]te the Earth. These giants gave rise to mighty dinosaurs, airplane-sized pterosaurs, huge crocodiles and snakes, and even car-sized armadillos. But today, there are only a few large animals on our planet. What happened? Why are there not many giants left?

First of all, there's plenty of fossil evidence that the ancient past really did have larger animals, beasts that were huge but also larger, on average, than creatures today, Greg Erickson, a vertebrate paleobiologist at Florida State University in Tallahassee specializing in ancient reptiles.

Ever since scientists unearthed the first known cache of dinosaur bones in the 19th century, researchers have come up with ideas to explain why giants were common millions of years ago, but less so today. "But no one can point to a definitive answer," Erickson said. "It's so multifactorial."

 

However, several important differences between dinosaurs and today's largest animals, mammals, may help explain the loss of the giants. Along with other giant reptiles, dinosaurs could adapt to different niches as they grew older, hunting smaller prey as young and larger victims as adults. In part, he might do this because they exchanged sets of teeth throughout his life.

 

Several important differences between dinosaurs and today's largest animals, mammals, may help explain the loss of the giants (REUTERS)
“They constantly replace their teeth, just like sharks. But along the way they could change the type of teeth, “Erickson remarked. Crocodiles, for example, go from “needle-shaped teeth to more robust teeth. Mammals don't have that luxury."

Put another way, when some young reptilians morphed into burly adults, they traded in their relatively weak juvenile teeth for larger weapons, which allowed them, in turn, to hunt larger meals to feed their larger bodies.

In dinosaurs, too, air sacs probably extended from the lungs to the bones, creating a tough but lightweight scaffolding, University of Edinburgh paleontologist Steve Brusatte told Scientific American. "That gave skeleton dinosaurs that" were still strong and still flexible, but light. That helped them grow and grow bigger and bigger,” Brusatte said.

 

He added: "In the same way that skyscrapers are getting bigger and bigger because of the internal support structures." (Of course, even though air sacs help build strong, lightweight bones, no animal could ever get as big as a skyscraper. That's because body weight grows much faster than bone strength as animals grow larger.) increase in size, as explained by physicist Neil deGrasse Tyson).

 

As warm-blooded, or endothermic, creatures, mammals also need a lot of fuel (REUTERS)
Mammals, however, lack these air sacs, "which can invade bone and lighten it," Brusatte said, "so the size of an elephant or a little larger might be the limit as far as mammals can go, at least on land. It doesn't seem like mammals can be the size of dinosaurs."

As warm-blooded, or endothermic, creatures, mammals also need a lot of fuel. "Elephants are totally endothermic, whereas dinosaurs, at least herbivores, probably weren't," Geerat Vermeij, professor of geobiology and paleobiology at the University of California, Davis, told Live Science. "So the food requirement for, say, a gigantic elephant would be maybe 5 times that of even the largest dinosaurs."

Paleontologists have debated whether dinosaurs were warm or cold blooded. But current science places many animal species on a gradient between cold-blooded and warm-blooded, and dinosaurs were probably "at the low end of the warm-blooded range," according to Erickson. That made a large body energetically less expensive for dinosaurs.

 

The huge size also requires the right environment. In a 2016 study published in the journal PLOS One, Vermeij concluded that gigantism depends primarily on sufficient resources being produced and recycled by "highly developed ecological infrastructure." In other words, the ecology needs to produce enough oxygen, food, and habitat for a truly giant creature to grow. Such ecologies had undergone a major development in the mid-Triassic period, near the beginning of the age of the dinosaurs, Vermeij wrote.

Giantism researchers must also not forget the crucial ingredient of time. Although animal lineages tend to get larger over the generations, for Erickson, a large amount of evolutionary time is needed to reach gigantic size (Cuartoscuro.com)
In a potentially important environmental change, ancient atmospheres have higher concentrations of oxygen. This may have influenced gigantism, especially of insects. The wingspans of the largest insects in prehistory followed the rise in oxygen concentration in ancient times, according to a study published in 2012 in the journal Proceedings of the National Academy of Sciences.

Giantism researchers must also not forget the crucial ingredient of time. Although animal lineages tend to get larger over generations, for Erickson, a great deal of evolutionary time is needed to reach gigantic sizes. And according to Vermeij, mass extinction events will have to wipe out larger creatures, so these events may leave gaps of giant animals unfilled for tens to hundreds of millions of years. "The first mammals took about 25 million years to reach a ton of weight," he explained. In the case of woolly mammoths, decimated by climate change and human hunters just 10,000 years ago, it may not be a coincidence that modern humans don't see such huge creatures: our own ancestors helped kill them not so long ago. weather.

 

For Vermeij, the most complete explanation for the decrease in size does not come from physiology or environment, but from social structure. “The evolution of organized social behavior, not only of herds, but of organized hunting in mammals, introduced a new form of dominance. Group hunting by relatively small predators makes even very large prey vulnerable. Individual gigantism has been superseded on earth by group-level gigantism,” he wrote in the 2016 study. That is, smaller individuals working together, as with wolves and hyenas, for example, can constitute a more efficient way to get big than building a huge body. "As a result, gigantism lost its shine on land," Vermeij wrote.

Social organization may also help explain a fairly large exception to the timeline drawn here: In the ocean, the largest animals in history still exist: blue whales. According to Vermeij, life in the sea makes it difficult to communicate over long distances, which makes it difficult to develop complex hunting groups. "The evolution of these groups has occurred on land much more than, at least until recently, in the ocean, as in the case of killer whales," he concluded.

 

Link https://www.infobae.com/america/perrosygatos/2022/06/08/por-que-razon-ya-no-hay-tantos-animales-gigantes/