I'm designing an alien race that in structure to humans. One exception is that they have long muscular tails.
I remembered while I was designing them, the reason why humans have no tails is because for us they were useless appendages.
Which begs the question, "if they're humanoid as well, wouldn't tails be useless for them?"
One option I considered was that their ancestors used to live on top of huge trees and therefore they needed the tail to get a better grip, but in reality would a humanoid race have such an appendage?
Other notes on their design:
- they have four arms
- raptor like legs
- elongated skull sort of like xenomorphs.
- their planet has a bit lower gravity)