This is something that people often ask, the question assuming that there are no intermediate fossils. The truth is that it is not easy for an animal of the past fossilize, as they require special conditions, as well as some parts of this that can mineralize "forever", as the bones. Therefore, finding fossils of invertebrates is virtually impossible (unless they have shells or the like). However, paleontology has taught us that there are indeed fossils that allow us to observe the transition from one species into another, sometimes very clear, as in the case of whales. Let the great biologist Richard Dawkins explain us this:
Another fossil that allowed us to understand the transition between fish and tetrapods (four-legged land animals) was Tiktaalik roseae, a fish of the Devonian, dating back some 375 million years, which is described by the following Wikipedia way:
"Tiktaalik was primarily the characteristics of a fish, but with the tips forming skeletal structures similar to an arm, similar to those of crocodiles, including shoulder, elbow and wrist. He had the sharp teeth of a predator, and his neck was move independently of his body, it is not possible in other fish. The animal also had a flat skull and the crocodile; eyes on top of the head, suggesting that spend much time looking up, neck and ribs like those of tetrapods, which will serve to support the body and help you breathe through the lungs, a long snout able to hunt dams on earth, and one gill opening, in more advanced animals would become heard. Its discoverers felt that, in all likelihood, Tiktaalik flexed its proto-limbs in the main river bed and could have pushed himself to the shore for brief periods. These specimens reached a size of 1.2 to 2.75 meters. "
If you do not imagine it, Tiktaalik had the following appearance:
In this diagram we can understand how did the transition from water to land:
Such examples are many more. Paleontology offers a grain of sand in favor of the theory of evolution, slowly but surely, and probably even many spectacular fossils waiting to be discovered.
Sources on Tiktaalik:
- http://es.wikipedia.org/wiki/Tiktaalik
- http://www-news.uchicago.edu/releases/06/060405.tiktaalik.shtml
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