In previous articles we have looked at the possible methods by which protocells could have started and later evolved into prokaryotic cells and eventually, eukaryotic life. These were very distant events occurring in the Precambrian period around 2-3 billion years ago (2-3 thousand Ma ago). Taking the view that the Invertebrata predates the Vertebrata, I have also considered some of the suggestions how Chordates (simpler precursors to the Vertebrates) could evolve from Invertebrates. This article continues the story and involves events sometime later. The examples of life I have selected are those of whom we have evidence of arising during the geological period referred to in the title of the sub-heading. They are also included because they help tell the story of the Tetrapods and/or they are interesting in their own right, I just like them!
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