Question

What was the first animal on earth?

Answer 1

The first animal is reported to have evolved in the sea over half a billion years ago. For some approx four billion years, no life existed on Earth, more complex than a simple cell. Then for some reasons that are still unknown, about 575 million years ago multicellular life forms suddenly began to multiply.

Complete answer:
Earth's first animal was the ocean-drifting comb jelly, not the simple sponge, according to a new finding that has shocked scientists who didn't imagine the earliest creature could be so complex.
The mystery of the first animal inhabitant of the planet can only be inferred from fossils and by studying the related animals today. The new study surprisingly found out that the comb jelly was the first animal to diverge from the base of the evolutionary tree, not the less complex sponge, which had previously been given the honor. "This was a complete shocker,"
The results were detailed in the April 10 issue of the journal Nature. A journal that, like the most respected journals, requires other scientists to review a paper before this publication. Unlike sponges, comb jellies have connective tissues and a nervous system, and so they are more complex. Though squishy and tentacled, they are not true jellyfish as they lack the classic bell-shaped body and characteristic stinging cells.

Note:
The first is that the comb jelly evolved its complexity independent of other animals after branching off to forge its path. The second is that the sponge evolved its simpler form from the more complex form.