Researchers believe that animals, especially terrestrial species, are limited in size due to the law of allometric growth and the abundance of resources.
The largest animal ever to walk the Earth is likely the Argentinosaurus, a titanosaur species weighing 70 tons that lived around 90 million years ago at the end of the Cretaceous period. In comparison, the heaviest terrestrial animal today is the African elephant (Loxodonta), which weighs less than 6 tons. However, both species are quite small when compared to the blue whale (Balaenoptera musculus), which averages 150 tons and may be the heaviest animal ever to live on the planet. But how large can animals actually grow? Are there limits to their size?
Argentinosaurus may be the largest dinosaur ever to exist. (Photo: Warpaintcobra).
“We look at blue whales and the question is whether there is an animal larger than that?” said Geerat Vermeij, a professor of geology and paleontology at the University of California, Davis. “I’m not sure of the answer because size depends on many factors.”
However, at least theoretically, there is a limit based on physical laws, which is around 109 tons for terrestrial animals, according to Felisa Smith, a professor of paleobiology at the University of New Mexico. To grow larger, the legs would need to be wide enough to support the body to the extent that the animal could not move effectively.
Smith is referring to the square-cube law, a principle first described by Galileo Galilei. According to this law, as an animal increases in size, its volume grows faster than its surface area, meaning that larger animals require proportionally larger limbs to support their weight. If you were to increase the size of an elephant several times over, the square-cube law indicates it would collapse due to its limbs not scaling appropriately with its mass. The only way for a supergiant elephant to overcome this limitation would be to have unusually large legs. However, at a weight of 120 tons, the legs would become impractically cumbersome. According to Smith, the largest animal recorded in the fossil record weighed less than 90 tons, supporting the theoretical maximum limit.
But physics is not the only barrier to animal size. The availability of resources is also an important factor. Animals living in more abundant environments with high-quality food can achieve larger maximum body sizes, according to Jordan Okie, a biologist at the University of Arizona. Whales, elephants, and many other large animals tend to inhabit nutrient-rich environments.
The demand for nutrients also explains why reptiles like titanosaurs are much larger than the largest terrestrial mammals. Because warm-blooded mammals have a faster metabolism, they require ten times the amount of food that reptiles need to grow to a similar body size. On the other hand, because they have lower body temperatures and slower metabolic rates, reptiles can eat less and require fewer calories than mammals. “It’s no surprise that the largest dinosaurs were over 10 times larger than the largest mammals,” Smith noted.
The blue whale can weigh around 150 tons and is a warm-blooded mammal, making it an exception to these rules. But their unique habitat may explain their success. Large animals in the ocean can leverage buoyancy to grow in size without placing stress on their muscles and skeletons. “Animals in water are less constrained by biomechanical limitations. The ocean also provides abundant, nutrient-rich resources for them,” Okie explained. “Specifically, the evolutionary development of the baleen allows whales to efficiently consume plankton sufficient to support their gigantic size.”
