It seems like any animal could benefit from thumbs.
In: Biology
Just because something *could* be of benefit doesn’t mean it will actually evolve. There needs to be incremental benefit across all the stages from finger to thumb, and each of those increments need to have a tangible effect on how likely the animal is to survive until reproduction. Primates evolved thumbs out of sheer necessity, not because it was just beneficial. Every other animal either doesn’t need to grasp anything at all, or can grasp the things it needs to grasp with other evolved mechanisms: Snakes for example grasp tree branches by wrapping around them, which is adequate enough – growing hands and thumbs would not be of significant benefit, and could be a serious problem, so it doesn’t happen.
Also, for the record, thumbs would make walking much harder for quadrupeds, so it would be a disadvantage for the vast majority of animals. Being bipedal isn’t optimal for most animals either, because bipeds are poorly balanced, slow and clumsy, with crappy spines.
Doesn’t matter if they would benefit from them, it needs a random mutation to develop in favour of it, and then that mutation to provide reproductive benefit.
It’s s complicated mechanism that requires the devotion of substantial brain resources to operate effectively. The benefit isn’t worth the cost to a dog or cat, in terms of increases survival and more offspring.
[Thumbs are not actually unique to primates](https://en.wikipedia.org/wiki/Thumb#Other_placental_mammals). There is evidence of opposable digits in pandas, rodents, marsupials, and more. [Even some cats can have thumbs](https://media.giphy.com/media/KtKi9n1k5h5bW/giphy.gif), although they were likely selectively bread for them. While humans and other primates might have the most complex and useful version of a thumb, other species have also managed to find an evolutionary advantage with it.
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