Possibly the largest animal to ever walk the earth is the dinosaur Argentinosaurus, a massive 77-tonne (70 metric ton) titanosaur that lived about 90 million years ago during the late Cretaceous period. For comparison, the heaviest animal on Earth today is the African the elephant (Loxodonta) that weighs less than 7 tonnes (6 metric tons). And they both look positively cute alongside the blue whale (Balaenoptera musculus), which at an average of 165 tonnes (150 metric tons), may be the heaviest animal that ever lived.
But can any animal outgrow that? Is there a limit to the size an animal can reach?
“We look at blue whales, and the question is whether we can achieve anything bigger,” Gerath Vermige (Opens in a new tab), professor of geology and paleobiology at the University of California, Davis, told Live Science. “I’m not sure I’d be willing to dismiss that question. Size depends on so many factors, and I take a relative point of view.”
Although, in theory at least, there could be a hard limit – enforced by the laws of physics – of about 120 tonnes (109 metric tons) for wild animals, according to Felissa Smith (Opens in a new tab)Professor of paleoecology at the University of New Mexico. “To be any bigger than that, on Earth, your legs would have to be so wide to support your body that you couldn’t walk efficiently,” she told Live Science in an email.
Smith points out Square cube law (Opens in a new tab), a mathematical principle first described by Galileo Galilei as “the proportion of two volumes is greater than the proportion of their surfaces.” In other words, as an animal gets larger, its volume will grow faster than its surface area, so larger animals need larger limbs to support their weight. If we were to just increase the size of an elephant by several orders of magnitude, the cube-square law would say that it would collapse—its mass would increase by a power of three, while its limbs would increase in volume by a power of two.
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The only way our huge elephant could get around this limitation was to have disproportionately large and thick legs. But even then, at about 120 tons, the limbs needed to keep an elephant afloat would become unbearably huge. The largest animals in the fossil record weighed just under 100 tons [90 metric tons], which supports this theoretical maximum,” Smith said, adding that “it is not clear that larger firms could not have evolved.” “
But physics isn’t the only limitation on animal size. If that were the case, we would live in a world full of 100-ton wild animals, and play carefully with Galileo’s cubic line. The availability of resources is also an important factor – megafauna must eat. “Animals that live in more productive environments with higher quality foods are generally able to harbor maximum larger body sizes,” he said. Jordan Aoki (Opens in a new tab), a quantitative biologist at Arizona State University. “Whales, elephants, and other myiabiota plants tend to live in productive, nutrient-rich environments.”
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The nutritional requirements also explain why reptiles, such as titanosaurs, grew so much larger than even the largest land mammals, according to Smith. Smith explained that because warm-blooded mammals have faster metabolisms, they require about 10 times as much food to support a given body size compared to reptiles. On the other hand, reptiles have lower body temperatures and slower metabolisms, so they can eat less and can grow on a caloric budget that would starve mammals.
“It’s not surprising that the largest dinosaurs in terrestrial regions were about 10 times larger than the largest mammals,” said Smith.
Blue whales, which can weigh around 165 tons and are warm-blooded mammals, are glaring exceptions to many of these rules. But hmm Their unique environment explains their success (Opens in a new tab). Megamarine animals can take advantage of their buoyancy to expand in size without straining their muscles and bones, and they grow in ways that would cause land animals’ limbs to collapse. And the whales have miles of open ocean at their disposal, which they travel to catch up on their meals.
“It is expected that animals in water will be less constrained by biomechanical constraints,” Oakey told Live Science in an email. “The oceans also provide abundant, nutrient-rich resources for these mobile and resourceful animals.” Oki added that the evolution of baleen slabs in particular allowed whales to consume zooplankton efficiently enough to support their massive sizes.
Various restrictions aside, the planet can clearly support megafauna. For hundreds of millions of years, megafauna were widespread. However, over the past twenty thousand years or so (Opens in a new tab), Just a blink of an eye in the time of evolution, megafauna has almost disappeared. Large land mammals such as elephants and rhinos are in decline, and are only found in certain parts of the world; Many groups of marine megafauna, such as whales, perpetually teeter on the brink of extinction. So where did all the giants go?
“Most of them were wiped out by humans,” Vermeig said. “Mammoths, elephants, bison, large carnivores – we’ve wiped out 90% of the large animals, maybe more, certainly all the large animals.”
Humans are also the main obstacle to reviving this large species.
“You don’t have to have humans before the megafauna can come back,” Vermeig said. “We are the dominant species, by far, and no animal will ever grow up under our domination. The chances of getting anything the size of a Cretaceous dinosaur again is unlikely.”
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