I don't know enough about the Shonai to speculate about that, so I'll have to do some research before I comment, but the Assegai spears were very short, with long leaf-like blades, almost like machetis or swords.
The Assegai spear, by the way, was originally a Berber weapon, that spread throughout Africa-and don't be confused, because the Zulu actually refined the original Assegai design, making the blade larger and broader, and naming the new weapon the "Iklwa" or "Ixwa". So, there's a little bit more to the story than was told in the Shaka Zulu miniseries (quite good, though) that ran when I was younger man.
http://therionarms.com/antiques/central_africa.shtml
This website has some nice pictures of African weaponry. There was also, years ago, a very good Dragon Magazine article (atleast for fantasy purposes) on the more unusual African weapons, but I couldn't tell you which issue it was in.