Personnel composition change of Dark Lord's forces

[Hisoka Morrow]

In the 1st age, the Dark Lord's forces were composed of a variety of creatures apart from orcs, in particular those so called "animals units", fled with Glaurung during Unnumbered Tears. However, we could seldom see these units appear in the latter timeline apart from several cases such as Minas-Ithil mentioned to get occupied by all kinds of fallen creatures and so forth. Any personal or authorized sources from JRRT, whether they're direct or implied sources or not?

 

[Aldarion]

We see Sauron making use of wolves in The Hobbit and also the Fellowship of the Ring. Other than that, however, I cannot recall any.

And "fallen creatures" could easily refer to orcs and trolls, as they are "fallen" variants of the elves and the ents, respectively (and even if not, they are in the service of the Dark Lord and thus "fallen from grace").