Today, Earth is home to animals of all shapes and ... and evolved over millions of years of evolution. But what was the first animal on the planet? The answer to this question is heavily debated ...

dramatically. It was the time of the Cambrian Explosion, an eruption of life when Earth’s very first animals began appearing in the fossil record — the ancestors of all major animal groups ...

The first life forms to appear on Earth were unicellular, i.e. composed of a single cell, such as yeast or bacteria. Later, animals -- multicellular organisms -- evolved, developing from a single ...