You get gold for assists.
Assist bounty is equal to 50% of the kill bounty, but that 50% is split up between everyone that assisted.
So if a kill is worth 300 gold the assist pot is 150 gold. If you did 90% of the damage and someone else secures the kill, it's quite likely you're the only person who assisted with the kill and you'll get the full 150 gold pot.
If 2 people assist with the kill than it's 75 each, 3 people it's 50, 4 people it's ~38.
On that note: it's worth mentioning your entire team is much better off if each kill your team made had an assist associated with it.
If you're just going in 1v1 to get 100%-->0% kills while your opponents team up to get each kill: that 50% assist bounty can keep them even in gold if you've got 15 kills to their 10.
As such: sharing gold with your allies to efficiently utilize kill-bounty will improve your chances of winning much more than hoarding all the gold and glory for yourself.