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From water to land

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From water to land

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The early tetrapods were the first vertebrates to actually walk the solid earth. They began their conquest of land in the Paleozoic era around 360 million years ago. The question many paleontologists have been asking for a long period of time is whether the anatomy for locomotion on land was developed in water for swimming purposes, or if it was adapted after the creatures became terrestrial. Recent findings of fossils indicate that the transformations of the aquatic creatures happened underwater in order to help them survive in the changing world. When looking for answers, they had to examine forearm, hip, wrist, finger, and other bones, as well as the lungs or gills of the early tetrapod fossils. This information is critical in understanding the history and the process of growth and change. It aids in learning about human evolution.


Tetrapods are creatures with four limbs, hips, shoulders, fingers, and toes, which developed sometime after lobe-finned fish, and before the first fully terrestrial vertebrates. The earliest tetrapod known is Acanthostega. It is also considered the most primitive tetrapod. It is very close to its fish ancestry, but still anatomically far from its terrestrial relatives. These creatures still lived in water, but they had a lot of the terrestrial tetrapod anatomical characteristics.


Before tetrapods existed, all vertebrates were confined to living in aquatic habitats. The only animals that lived on land were arthropods. Through natural adaptations, the fish developed into amphibians. This colossal stage of change made necessary the evolution of new ways of breathing, locomotion, and reproduction. Paleontologists needed to understand how this transition took place. If the changes in anatomy of the fish developed on land, then they served the same purposes they serve today, such as walking. But what advantages would those same body parts give to the aquatic creatures still living in water? This is one of the questions the scientists are asking themselves. There have been a few hypotheses on this matter. The most recent one states that the transformations of the aquatic creatures happened underwater in order to help them survive. This time period is very difficult to study because there is a very small amount of fossils preserved. After all, this occurred approximately 350 million years ago; and since the first tetrapods lived in water, their remains were damaged as time went on.


. In 1940 Alfred Romer of Harvard offered a powerful scenario about the process of evolution of the fish into amphibians. He argued that the freshwater pools that the early tetrapods lived in were suffering seasonal droughts. He compared these early creatures to lungfish. Because of the draughts tetrapods evolved lungs and were able to breathe air when necessary. This happened over a long period of time. The lungs came to the rescue when the oxygen became scarce in water or when the ponds dried out. Romer also suggested that instead of digging burrows with their teeth, such as lungfish do in similar situations, tetrapods used their fins to struggle over the harsh land to the nearest pond. By the process of natural selection, fish with weak fins died along the way, but fish with strong ones lived to reproduce and pass on their genotype to their offspring. Gradually fins turned into limbs, which are much better for overland travel. At the same time, many other parts of the body, such as eyes, ears, and skin, changed to better cope with this new environment (Gardiner, 1998, p.659).

Romer's theory was very controversial because there were a lot ...

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