Two Questions about the Stone Giants.

[Noxomanus]

I think these Giants represent a different species of humanoid,untold of elsewhere in Tolkiens work.
They certainly weren't Hobbits,Dwarves,Druedain or Elves. No need for explaining why.

They could have been a sort of Orc or Troll but the fact that these are evil and Gandalf is on speaking terms with Giants seems to imply this isn't the case.

Ents are a possibility as these are very large and extremely strong, but Ents are connected with forests and don't seem to be of the violent kind,throwing rocks at bypassers or using them as a football. Huorns look like trees and are not humanoid,as the Giants do seem to be.

I don't think they were Ainur either as these would seem to be a bit more intelligent then these Stone-Giants and it seems all in all unlikely that they are Ainur.

It is a possibility that they were in fact a kind of Men. Men are quite diverse and this seems to have been the case in ME as well. And think about Samoans,those guys are huge and would really be Giants in the eyes of Hobbits,Dwarves and an old man bend over a staff. Not to imply Giants were Samoans but to mean Men can get very large and impressive.

And then,they could be beasts of some kind. It would be a good explanation of their rather violent play and lack of human-level intelligence. The fact that Gandalf could speak with them doesn't have to be an objection;The Wizards are said to have 'conversed with the people of ME and birds and beasts the like.'

To conclude I think these Giants are either Men,Beasts or a seperate kind.