Up until now accepted explanations of the "disproportionate" size of whales and other marine mammals mostly relied on the pressure (and buoyancy) of organisms living in the water and the growth without limitation of the water environment. It sounded promising, the five-tons elephant needs to be highly adapted to the land movement, while the thirty-ton whale is allowed to float in the water. Therefore, the elephant can not be much more difficult because its legs would not be squeezed while the whale is not limited in size. This traditional lay explanation is now being broken by Stanford researchers to the Padr. They point out that the aquatic environment presents much less freedom for mammals and brings much more functional limitations.
Metabolism is the boiler and its coal
The decisive factor is the effective rate of metabolism of marine mammals and the ability to maintain heat. "When you are a mammal, the situation is built as follows: it is not so much that the water environment will allow you to grow in size. You yourself have to be big, and you have no choice, " explains Craig McClain, co-author of the study. As? "In general, animals are like machines that need energy to function. And just that energy consumption limits what animals can do and how big they can be. "The driving mechanism is the metabolism that produces energy from the food intake. The power that makes up the consumption. And first of all, it is necessary to tune up the energy intake with its delivery.
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The growth of a small and several gram-weighing mammal would not last long in the aquatic environment. Since water quickly transfers heat from the body and maintains the hypothetical "sea mouse" in its condition, it must continuously feed its metabolism. Otherwise she would be undercover and death, which is not an optimal strategy for a happy life. But if it increased its body and its weight? At a certain point, food intake for the hungry metabolic boiler will be optimal with energy output and heat loss. And it's not a coincidence that this optimum weight (with a few exceptions) is between 500 kilograms.
It does not matter to the ancestors of marine mammals
"The size range of marine mammals is surprisingly very uniform, far less varied than in mammals living on land," says Professor Jonathan Payne, principal author of the study. It confirms this by statistics, or by analyzing the weight and body size data of 3859 living marine mammals (and 2999 samples of extinct ones). Indeed, marine mammals with extremely different terrestrial ancestors have consistently settled in development not only on a somewhat stunted body shape, but also on similar halftone scales. This is true for seals and seals (who have distant dog ancestors), cabbages (near elephants) and whales and dolphins, whose ancient terrestrial ancestors looked like hippos.
"The development of the evolutionary phylogenetic branches allowed us to estimate the size and weight of terrestrial ancestors of present-day marine mammals. There is a clear trajectory of change that they have to undergo, " adds Payne. Moving into the aquatic environment meant (in terms of phylogenesis) a lesser need for weight picking, for greater rather than a reduction to the optimal point. Sea mammals have had to adjust to their new environment. An entirely convincing explanation of the size and weight of marine mammals "scrubs" on two deviations: on unexpectedly small ocean otters and huge whales. Even the Stanford scientists have an explanation.
"From a purely evolutionary point of view, it is only recently that the sea otter has moved into the aquatic environment," explains McClain. "And he still spends a substantial part of his life on land, in close contact with the mainland." And whales? Kostic people really represent an extreme among mammals. "But it is because they invented a new way to eat. By continuously filtering the plankton from the water during their movement, they are actually continuously receiving energy for their metabolism. They do not fish for food or do not look for it, but they keep getting it all the time. " Other marine mammals that do not function as floating vacuum cleaners of microscopic plankton, but have no such option.
Author: Radomír Dohnal
Source: Ekolist.cz