Early Animal Phylogeny By _hannahgrace_11 Period: 600 BCE to 515 BCE 600 Million Years Ago to 515 Million Years Ago Choanoflagellates first appeared 600 MYA. Ctenophora first appeared 515 MYA. That is the timespan of this timeline, although the program does not allow for these dates to be entered. 1 CE Choanoflagellates (https://www.cell.com/current-biology/pdf/S0960-9822(05)00142-9.pdf) 2 Porifera Sponges 3 Placozoa 4 Cnidaria 5 Ctenophora
