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Size Does Matter: Why Aquatic Mammals Like Whales Need To Be Big, But Not Too Big

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Whales are inherently big, but scientists wonder why they do not ever get bigger. The answer: growth is constricted in water than in land.

A team of researchers from Stanford University studied whales and elephant seals to determine if they can get larger than their current size. The initial hypothesis is to debunk the common perception that aquatic animals tend to get bigger than their land counterparts.

Study findings revealed that growth in water is much more constricted than on land, which suggests that aquatic mammals are unlikely to grow bigger than their current size.

The study published on March 26 in the Proceedings of the National Academy of Sciences explained that large aquatic animals are bound to stay in their size to retain body heat and availability of food supply. This theory has debunked previous ones, stating that saltwater pressure allows more room for growth.

"Many people have viewed going into the water as more freeing for mammals, but what we're seeing is that it's actually more constraining," said study author Jonathan Payne, a geological sciences professor at Stanford School of Earth, Energy, and Environmental Sciences.

Payne further explained that being in the water does not mean that animals can be big. It is just that animals need to be big in the water for survival reasons.

New Environment, New Body Shape

It has been a common perception that aquatic animals may be related to one another due to the shape of their bodies. However, it is not necessarily true because many aquatic species can trace their ancestry back to land animals such as dogs and hippopotamus.

Stanford researchers have teamed up with Craig McClain, an expert from the Louisiana Universities Marine Consortium, to conduct an investigation on the physical characteristics of living and extinct animals.

A total of 3,859 present-day animals and 2,999 fossilized mammals were analyzed. Results showed that land animals evolve quickly as they transition to water environments. Such evolution is paramount to increasing their size because as it turned out, "bigger is better for aquatic life" but up to a certain weight or length only.

Will Gearty, a graduate student of Stanford, said that by analyzing family trees in the animal kingdom, scientists are able to understand how one species is related to another.

Another valuable explanation with regard to whale size is the ability to retain body heat. Smaller aquatic species tend to lose body heat more quickly than their larger counterparts.

However, McClain said that whales and other similar-looking mammals can only grow up to a certain size due to metabolism factor. The bigger they get, the faster their metabolism is, which means that they need to constantly look for food in a scarce environment.

Meanwhile, there are exceptions to the rule. Baleen whales, for example, spend less energy on hunting and consuming food because of their filtration ability. Toothed whales, on the one hand, have to exert more effort in munching and digesting their food.

Payne's team's groundbreaking findings shed light that animals' eating behaviors affect their size whether they live in land or in water.

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