If I understand the evolution correctly, it is stated that a land mammal returned to the ocean to become a whale.
Some populations of ungulates did that, a little at a time, starting with animals that could run on earth, but were able to wade around in shallow water. (Pakicetus)
How did it survive the evolutionary process?
Gradual change, filling different niches on the way. The usual.
Just because a fossil of a whale with legs has been found
Quite a number of different species now. And every now and then, a modern whale is born with vestigial hind legs. The genes for legs are still there, but they normally aren't expressed.
(though that's the first I've heard of it - could you provide a link for verification)
Thewissen JG, Williams EM, Roe LJ, Hussain ST.
Department of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272, USA. thewisse@neoucom.edu
Modern members of the mammalian order Cetacea (whales, dolphins and porpoises) are obligate aquatic swimmers that are highly distinctive in morphology, lacking hair and hind limbs, and having flippers, flukes, and a streamlined body. Eocene fossils document much of cetaceans' land-to-water transition, but, until now, the most primitive representative for which a skeleton was known was clearly amphibious and lived in coastal environments. Here we report on the skeletons of two early Eocene pakicetid cetaceans, the fox-sized Ichthyolestes pinfoldi, and the wolf-sized Pakicetus attocki. Their skeletons also elucidate the relationships of cetaceans to other mammals. Morphological cladistic analyses have shown cetaceans to be most closely related to one or more mesonychians, a group of extinct, archaic ungulates, but molecular analyses have indicated that they are the sister group to hippopotamids. Our cladistic analysis indicates that cetaceans are more closely related to artiodactyls than to any mesonychian. Cetaceans are not the sister group to (any) mesonychians, nor to hippopotamids. Our analysis stops short of identifying any particular artiodactyl family as the cetacean sister group and supports monophyly of artiodactyls.
Nature. 2001 Sep 20;413(6853):259-60.
Oelschläger HA.
Zentrum der Morphologie, Johann Wolfgang Goethe-Universität, Frankfurt am Main, BRD.
The present paper is concerned with the comparative morphology of the archeocete and odontocete skull. Among the archeocetes, the recently described lower Eocene Pakicetus inachus obviously represents an early stage of adaptation to aquatic life. The morphology of the incomplete cranial remains, however, gives no evidence that Pakicetus was an amphibious intermediate stage. The evolution of advanced archeocetes and odontocetes is characterized by the successive acquirement of new morphological devices related to the emission and perception of ultrasound under water. The formation of a sonar system in odontocetes obviously not only helped to compensate for the loss of the peripheral olfactory system but moreover was a substantial factor in the evolution of the exceptional dolphin brain.
Gegenbaurs Morphol Jahrb. 1987;133(5):673-85
doesn't mean that it came from a land dwelling ancestor.
Yes, it does. The first known one had the skull of a very primitive whale, but the body of a running animal, complete with hooves.
It could have been a genetic defect.
It would have been, if the niche for an amphibious coastal carnivore/scavenger wasn't available.
There is no way for science to prove that it is a step in an evolutionary process.
It's not just that we have a series of gradually-modified land animals. We also have genetic information, of the same sort they use to determine paternity, so we know it works. We also have all these obvious whales with legs, and then even some modern whales born with vestigial legs.
Oh, and they still have an ungulate digestive tract. Never needed to change it, I guess.
Don't get me wrong, I am not a young earth creationist. I believe the earth is millions of years old. I just don't think the science of evolution is as sound as evolutionists (a religion of its own) make it out to be.
I'm always surprised that those who think they hate science, call it a religion. Because evolutionary theory depends on evidence, it is a science. Creationism, being based on faith, is a religion.
What did God create when He first created the earth? I don't know. What evolved and what didn't? I don't know.
Fortunately, there are ways to investigate such questions. God is not deceptive, and did not plant this evidence to fool us.