900 - 840
840 - 780
780 - 720
720 - 660
660 - 600
300M
900 - 600
60M
4th 250 M Galactic year 1 B - 750 M
3rd 250 M Galactic 750 - 500
Proterozoic Eon 2.5 - 540 M
Precambrian Time 4.5 - 543 M
Neoproterozoic 900 - 543
   
Vendian 650 - 543
- 900 - 543 neoproterozoic Neoproterozoic
- 900 Choanoflagellates are considered ancestors of the entire animal kingdom, and in particular may be the direct ancestors of sponges.
The choanocytes (collar cells) of sponges have the same basic structure as choanoflagellates. Collar cells are occasionally found in a few other animal groups, such as flatworms. Comparisons of DNA sequences support a close affiliation between choanoflagellates and animals.
- 850 Proterospongia (members of the Choanoflagellata) are the best living examples of what the ancestor of all animals may have looked like.
They live in colonies, and show a primitive level of cellular specialization for different tasks.
The similarities between Proterospongia and sponges are strong evidence for the close relationship between protozoans and metazoans.