The ancestors of baleen whales have increased in size because of the ice age, adapting to new conditions of supply.
Blue whale feeding on plankton is one of the largest animals that ever lived on Earth. (Photo: turbo thumbs / Flickr.com.)
Biologists have long debated why the whales became large. According to one hypothesis, they become so just because they could: water environment supports the weight and allows to move easily, so that the whale could easily find enough food even if the food is a tiny marine crustaceans.
According to another hypothesis, cetaceans have increased in size because of the huge predators that once upon a time inhabited the seas and oceans: not to fall into the jaws of a huge ancient shark, it was necessary to become as large as possible.
Let’s not forget that among the cetaceans, not all types of acquired gigantic dimensions . In 2010, Graham Slater (Graham Slater) from the University of Chicago in Illinois suggested that in the course of their evolutionary history, cetaceans have become such as they are, pretty early: around 30 million years ago appeared on Earth the ancestors of modern dolphins, who were, like their modern descendants, is relatively small, the ancestors of the “mid-size” carnivorous toothed whales and the ancestors of baleen whales that feed on plankton and which quickly reached a very impressive size.
Now, however, the same Graham Slater and his colleagues, Jeremy Goldbogen (Jeremy A. Goldbogen) from Stanford and Nicolas Pyenson (Nicholas D. Pyenson) from the National natural history Museum, writing in the Proceedings of the Royal Society Bthat it was not quite so. A few years ago we found out that the body mass of cetaceans correlates with the size of the zygomatic bone.
Comparing skulls of several dozen extinct and extant species, the researchers came to the conclusion that, divided into several groups, the whales initially grew up not too actively, for quite a long time, even the large species did not exceed 10 m length. Only about 4.5 million years ago there was a breakthrough, and baleen whales were sharply increased in size. What happened then? The authors believe that all the matter in the then ice age: the advancing glaciers were regularly melted and carried away in the ocean a lot of nutrients, which served as food, small crustaceans and other small animals.
Baleen whales, as we mentioned above, produce food, vyziva of water varied animal detail. It is very important that you have a big mouth: what it is, the more effective you will filter your own food. In other words, feeding on plankton, it is better to be big than small. At the same time, plankton is distributed unevenly over the ocean – there is a zone, a kind of planktonic fields where a lot of it, and, in addition, due to issues with climate now in different seasons was a lot, little.
The whales have to swim from one field to another, and to do it better if you again great body. So we can say that baleen whales are large because of the food – plankton-eating species, has a modest size, simply died out, unable to adapt to the new diet.
On materials Science.