It bugs me when I miss something as obvious as the relationship between Greek tauros, (Latin taurus) and Spanish toro for "bull." Benjamin reassures me that I keep noticing these things all the time, unlike normal people, and keep kicking myself at each new one for not having noticed it before. I suppose.
It's a great opportunity to go trace it back into Indo-European, to see if there's anything interesting about it. There usually is. In this case there is the mildly interesting aspect that the reconstructed Indo-European *tauro is derived from an earlier root *sta-. The dropping of an initial s is only moderately common.
More interesting is the earlier *sta-, meaning "to stand," and giving rise to stay, stand, stable, steed, stud, stage, constant, and dozens of others. The idea is of a permanent place where something - originially stockbreeding - was done. In Pashtun it leads to -stan meaning "place," as in Afghanistan, "place of the Afghan people," Pakistan "place of the Pakis people."
Okay, so that's not frightfully interesting just yet. But wait, there's more. The roots *stak (stand, place), *stel, (put, stand), *steg (pole, stake, stick), and perhaps even *stai (stone) and *stebh (post, place firmly on) suggest an even earlier root around this "sta" sound. There seems some connection of place, solidity, standing in place, stability, doesn't there?
But there aren't supposed to be any observable earlier reconstructions beyond the Indo-European, according to most linguists. The linguistic distance is supposed to be too great, and all such connections unreliable.
Except that it's pretty clear, isn't it? One more small point that Greenberg and Ruhlen are right.