My main work is soft sci-fi and is aimed at the young adult audience or possibly juvenile audience. I've pulled away from direct Earth references. I have multiple alien species but I still refer to the humanoid characters as humans. In describing some of the aliens, I use descriptions like "fox-like" or I compared one species to kangaroos. Two of the species have multiple races. For the dog-like species, I compare one of them to a German Shepherd. My question is, should I stay away from using such obvious Earth related descriptions if I'm not setting my story within Earth based world building? Thoughts?
For animal types, I think calling them by the species name is fine. Otherwise, it gets cumbersome. Birds, bugs, ect, all have to be renamed, and then, if you think about it, plants should be renamed as well. If you don't want to call a fox a fox you can do something like: 'The _____ emerged from the undergrowth, a small, 20 lb predatory creature with reddish-brown fur, long, thin legs, lithe frame, pointed nose and bushy tail." I'd say avoid giving specific breed names like 'German shepherd'. Unless you happen to have a country called Germany for whatever reason on the alternate world.
If you're using earth based names to discribe anamorphic characters, perhaps referencing lore from various cultures would be helpful. Egyptian, japanese, chinese, nordic, and greek cultures all have a wide variety of monsters and deities based on animals. Unless you ask for suggestion on specific animal traits i can't really be more pointed than thus. Sorry.
By “alien species”, I presume you mean intelligent species, right? And by different races in a species, using the “dogs” as an example, like having German Shepherds and Saint Bernards? Since this is for the more youthful audience, why not? Would save you a lot of time. However, I would not call the individuals “humans” but “persons” instead. After all, one of those pseudo German Shepherds may get ticked off at being called “human”.