Phylogeny help? Homo Sapiens - Sahelanthropus tchadensis?

[kitty]

I have a phylogeny assignment for my anthropology class in which I have to take the following species, and place them in a phylogeny. I have to make a graphical representation that also shows how long the species existed, a timeline, and show probable descent (the part I'm having difficulty with). Then I will have to explain why I placed each species where I did, why I chose one name or the other (the ones with parentheses can have one of two names) and why I chose to represent descent the way I did.

I am having a hard time with the descent part, how to arrange them, and how to back it up/explain why I chose it. I can find images online of possible descent, but not WHY it is this way.

The species are these:
Homo sapiens sapiens
Homo (sapiens) neanderthalensis
Homo erectus
Homo habilis
Australopithecus (Paranthropus) boisei
Australopithecus (Paranthropus) robustus
Australopithecus (Paranthropus) aethiopicus
Australopithecus (Homo) sediba
Australopithecus africanus
Australopithecus garhi
Australopithecus afarensis
Australopithecus anamensis
Ardipithecus ramidus
Ororin tugenensis
Sahelanthropus tchadensis

Extra Credit species are:
Homo floresiensis
Australopithecus (Kenyanthropus) platyops


I would really appreciate any help, I only have a few days to do this. I am trying to work it out using my book but I feel SO lost right now.