Aliasing tortoise → turtle
Link to alias
Reason:
tldr: Neither term is particularly well-defined. Turtle is already established on e621 (more common, already has implications) so...turtle.
The exact usage of the two is debatable, particulary due to regionalisms. In the US, turtle is a catch-all term and includes tortoises, in the UK they are generally separate creatures depending partially on behavior, in some other areas I've heard tortoise is sometimes used as the catch-all term. There's also terrapins which...well you get the idea. Point is, there isn't even an easy way to consistently tag the two. Also, I doubt that many people would look for one and want to exclude the other.
Updated by Furrin Gok