How big can animals get?

illustration of Argentinosauruspossibly the largest dinosaur that ever existed. (Image credit: Warpaintcobra via Getty Images)

Dinosaurs were probably the biggest animals to walk on Earth. Argentinosaurus, A giant titanosaurus that weighed 77 tons (70 metric tons) and lived during the Late Cretaceous period about 90 million years ago. For comparison, the heaviest animal on land today is African elephant (Loxodonta) and weighs less than 7 tons (6 tons). And both look positively dainty on the side blue whale (Balaenoptera musculus) averaged 165 tons (150 metric tons), making it possibly the heaviest animal to ever live.

But is there any animal that surpasses it? Is there a limit to the size an animal can grow to?

“We’re looking at blue whales. The question is can we get something bigger?” Geerat Vermeij a professor of geobiology and paleontology at the University of California, Davis, told Live Science.

But at least in theory, land animals might have a hard limit (enforced by the laws of physics) of about 120 tons (109 metric tons). Felisa Smith, professor of paleoecology at the University of New Mexico. “To be larger than that, on land, the legs must be very wide to support the body, so they cannot walk efficiently.

Smith mentions square cube rule is a mathematical principle first explained by Galileo Galilei that “the ratio of two volumes is greater than the ratio of their surfaces”. In other words, as an animal grows in size, its volume grows faster than its surface area, so larger animals need much larger limbs to support their weight. , by the law of the square cube, the elephant is considered to collapse. Elephant mass increases by a power of 3, and limb size by a power of 2.

Elephants are the largest land animals alive today.

The only way our fictional giant elephant can overcome this limitation is to have disproportionately large and thick legs. It’s unbearably bulky. “The largest animal in the fossil record is just under 100 tons. [90 metric tons]supports this theoretical maximum,” Smith said, adding, “It’s not clear that anything larger couldn’t have evolved.”

But physics isn’t the only limit to animal size. If so, we live in a world chock-full of 100 tons of land animals, carefully following the lines of Galileo’s square cube. Giant animals must eat. “Animals that live in more productive environments with high-quality food can generally accommodate larger maximum body sizes. Jordan Okey, Quantitative Biologist at Arizona State University. “Whales, elephants and other megafauna tend to live in productive, nutrient-rich environments.”

Nutrient needs also explain why reptiles like Titanosaurus became much larger than the largest land mammals, Smith says. Because warm-blooded mammals have fast metabolisms, they require about 10 times more food than reptiles to maintain a particular body size, Smith explained. Reptiles, on the other hand, have lower body temperatures and slower metabolisms, so they can afford to eat less and grow on calorie budgets that starve mammals.

“Not surprisingly, the largest land-based dinosaur was about 10 times the size of the largest mammal,” says Smith.

Blue whales, which can weigh about 165 tons and are warm-blooded animals, are a notable exception to some of these rules, but their unique environment explains their success. Large marine animals can use their buoyancy to increase in size without straining their muscles and bones, growing to the point where land animals’ limbs crumble. And whales have miles of open ocean at their disposal, migrating in search of food.

“Animals in water are expected to be less constrained by biomechanical constraints,” Okie told Live Science in an email. “The ocean also provides abundant and nutrient-rich resources for animals with great locomotion and resourcefulness.” In particular, the evolution of baleen plates has allowed whales to efficiently consume zooplankton, reducing their enormous size. Okie added that he was able to maintain it.

Aside from various constraints, planets can obviously support megafauna. For hundreds of millions of years, megafauna lived extensively. However, over the past 20,000 years, in a fraction of an hour of evolution, megafauna almost disappeared. Large land mammals such as elephants and rhinoceroses are declining and live only in certain parts of the world. Several groups of marine megafaunas, such as whales, are continuously endangered. So where did all the giants go?

“Humans have eliminated most of them,” said Vermeij. “We have eliminated 90% of the large animals, probably more, and all of the largest animals, including mammoths, elephants, bison, and large carnivores.”

Humans are also the main obstacle to the resurgence of these large species.

“The humans need to be gone before the megafauna can be resurrected,” said Vermeij. “We are by far the dominant species, and no animal will grow in size under our hegemony. It is highly unlikely that we will ever again have something as large as a Cretaceous dinosaur.”

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