What was the first animal on earth and how was it born or made?

Question: What was the first animal on earth and how was it born or made?
- Keywords:
  evolution,
  first animal,
  life
Asked by yumna to Arttu, Ceri, James_M, Monica, Philip on 16 Jun 2011. This question was also asked by ahmed.
- Arttu Rajantie answered on 16 Jun 2011:
  
  This is not really my field, but I guess the first animal would have been something very simple and quite different of the animals that exist today. I would imagine that some single-cell micro-organisms were forming colonies where they gradually became so dependent on each other that the whole colony started to behave like a single organism.

Question: What was the first animal on earth and how was it born or made?