Is there a limit to how big animals can grow?

Joshua A. Krish poses this question in his article in Live Science (March 2023) and he says that there is a limit – animals can’t grow indefinitely.

The largest land animal is the African Elephant (Loxodonta africana) which is a mammal that reaches 250 centimetres (8 feet 4 inches) tall and 750 centimetres (25 feet) long, weighing about 6 metric tons (7 tons). It is not a meat-eating carnivore. It is an herbivore and eats grass, trees, bushes, fruit, and bark.

The largest ocean mammal is the Blue Whale (Balaenoptera musculus) which can grow to 30 metres (98 feet) in length and weigh 150 metric tons (165 tons).

Size depends upon many factors, but it is unlikely that mammals will get bigger and bigger. In theory, and mathematically, there is a limit to how big animals can grow. 

Professor of Paleoecology, Felisa Smith, at the University of New Mexico, thinks that the limit for land animals might be about 109 metric tons (120 tons). How can a land animal be bigger than an elephant or bigger than the largest prehistoric land animals, which were under 90 metric tons (100 tons) in weight? ‘To be bigger than 120 tons, your legs would have to be so wide to support your body that you couldn’t efficiently walk,’ says Felisa Smith. 

Felisa Smith used the mathematical ‘square-cube law’ to determine the biggest possible size that a land mammal can grow to. Scientist Galileo Galilei (1564-1642) first introduced the square-cube law, which is a mathematical principle that says ‘the ratio of two volumes is greater than the ratio of their surfaces’ – which means that as an animal increases its size, its volume will grow faster than its surface area. The result is that larger animals need much larger limbs to support their weight.

But there is no point for a animals to have really, really thick legs to support their weight if they can’t escape a predator or move to find food. Mega-animals (or megafauna) would need a lot of food. 

Blue Whales live in an environment that can fulfill their food requirements and they don’t need big legs. Marine mega-animals are buoyant – their weight is supported by water, and therefore there is no strain on their muscles and bones. Blue Whales also have a lot of water in their environment in which to search for food. Despite being the largest animal on Earth, it feeds on one of the smallest marine animals in the ocean – a tiny shrimp called Krill. 

Many hundreds of millions of years ago, Planet Earth used to have megafauna, but about 20,000 years ago they became extinct. Today’s large animals, such as elephants and rhinos only live in small areas of specific countries – and their population numbers are declining. Humans are their main threat.

Location of photographs: Kenya

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM