It was pointed out in the Inside the Worlds: Classic Trilogy book that Saurins are a sub-species of Trandoshans, explaining their similarities. Now unless my understanding of sub-species is totally off, it goes to say that the two are either minor variations of a common ancestor or one is a divergence of the other, though without any info on their split I suppose such guessing is moot.
My theory is that, given the improbability of another sapient species independently cropping up in the same system as another (there are examples, but I'm of the beleif they are very rare occurances or have explanations), the original Trandoshan/Saurin homeworld is Durkteel, or whichever is the Saurin's main, and that the Saurins are the more physically divergent of the two, specifically their hands geared for human interaction (it is more likely part of the species developed hands to better work in the galactic economy than to develop clumsier hands). The Trandoshans and their hunter-oriented culture likely left at some early point in time and set up a new home on an arid world in the isolated Kashyyyk system, possibly even terraforming it to some degree for habitability.
Meanwhile, the Saurins still on Durkteel begin or continue to interact with the galactic community, the hands of subsequent generations developing into more a useful mainstream shape (probably artificially, considering the arrangement and amount of digits, though it may have been simply to progress subtle changes already cropping up from beneficial mutations in hand structure). The Trandoshans do not experience these pressures and influences and remain relatively unchanged.
I wouldn't say it's a profound suggestion; it's not too far from the canonical example of Duros and Neimoidians and takes cues from Saxton's suggestions of galactic community-influenced evolution. It merely ties up their physical differences as well as explains the Trandoshan presence in Kashyyyk.
Apparently, this is now the part where comments or discussion come in.
