In the past few weeks, some new research regarding the Evolution of marine animals into land-dwelling animals has been published. It suggests that the gradual alteration may have been brought about by powerful prehistoric tides. The change, primarily the presence of walking limbs, occurred an estimated 400 million years ago, in the early Devonian Period.

Fishy features from today and yesterday

A few years ago, Scientific American's Christie Wilcox observed that it's not very hard to envision such an evolution just by watching modern Fish species alone.

Fish are quite capable of adapting to unique environments. For example, Wilcox pointed out the walking catfish, an aquatic creature which is capable of breathing out of the water for days at a time. She also mentioned other walking fish like the mudskipper.

The fossil record is full of examples of a variety of fish that have survived the test of time. The Coelacanth is related to tetrapods (creatures with four legs) and lungfishes. It's referred to as a living fossil because, though it was previously thought to be extinct, a living specimen was discovered in 1938. As we have seen, fish seem to be quite durable and, apparently, pliable.

Obviously, numerous factors contributed to the evolutionary steps that were taken and numerous features underwent changes.

For instance, as of 2014, scientists have known some prehistoric fish were able to breathe air via canals on the tops of their heads called spiracles. Such intriguing breathing mechanisms are still found in living specimens of fish like Polypterus.

So what (do we think) happened?

What many scientists consider the defining or most important feature which was upgraded was the limb, changing from fin or flipper to foot.

The extinct species most thought of as the missing link between sea and land animals is tiktaalik. This bony fish or fishapod possessed lungs, gills, unique fins, scales, and an adjustable neck. This organism paved the way which would eventually lead to the development of the tetrapods.

Recent studies have caused a new evolutionary concept to surface.

Several scientists have formed the hypothesis that prehistoric tidal activity may have drastically affected the evolutionary from sea creature to land animal. Millions of years ago, Earth's moon was about ten percent closer to our planet than in present day. Thus, tides were likely quite a bit stronger.

Fish frequently would have been stuck on the land or in small dwindling bodies of water. This dilemma may have spawned the feature of feet or legs. Tiktaalik is an example supporting this scientific notion. Interesting as it is, this tidal hypothesis will require more substantial data to be collected to support it.
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