Question about skull warrior and gargoyle.

I haven't built any Rams teams, so I'm unsure of how this works. Both the skull warrior and the gargoyle have, in their skill trees, a little arrow pointing from one skill to another.

I had assumed that it was a prerequisite, but someone pointed out to me that it might be different.

Can someone with experience point out how, exactly, those arrows work? Does it mean grabbing "taunt" limits you to getting "fierce" during skull warrior's level 4, or does it mean you can't grab fierce unless you've already grabbed taunt?

In the closed beta there were a lot of arrows and they were pre-requisites to get a certain ability. They removed more or less all of them with the open beta patch, so I don't know if those are simply a graphical error, but before they were pre-requisites.