We are very, very small compared to prehistoric creatures, especially dinosaurs. Besides dinosaurs, snakes, felines, and more remain a beast compared to their counterparts today.
Moreover, plants and insects were reaching incredible sizes. Then something happened and living things got smaller. So what was it that caused this huge impact?
The main reason why prehistoric life forms were so large was “oxygen produced by cyanobacteria”.
These microscopic organisms, which can be seen as a blue-green layer over lakes and seas, were able to obtain their energy through photosynthesis 2.4 billion years ago. Thanks to their photosynthesis with carbon dioxide, oxygen – waste for them – was released into the atmosphere and life forms on Earth changed drastically. The emergence of oxygen in the atmosphere is called the “Great Oxidation Event”.
Oxygen breathing organisms become more active and larger.
The amount of oxygen increased 800 million years ago, and further increased 500 million years ago. This excess of oxygen was an invaluable boon for the enlargement of living things. Living things, whose cells were filled with oxygen, became more agile and larger over time.
Then there was a mass extinction due to the meteorite impact and the oxygen level dropped drastically. Only tiny creatures that could survive on less oxygen survived this disaster.
According to Cope’s Rule, living things will still be great many years from now.
According to this idea, living things tend to grow as they evolve over time. Prehistoric creatures also reached gigantic sizes over time. 66 million years have passed since the extinction of these creatures, and this period is very short for living things to reach gigantic proportions again.
Oxygen may not be the only reason!
In those eras, land masses were larger, which means more area. It is known that creatures that evolved in a limited area, especially on islands, were smaller in size. Pygmies and aborigines from the island peoples are the best examples of this.
Sources: 1, 2, 3, 4, 5, 6
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