We can't say it's impossible, but we also have no examples in our planet. So we are stuck with speculation.
There are philosophers who believe that sentience and consciousness (which is something different, but also interesting) are emergent properties of the brain. Some scientists are looking into this, though it seems at the moment that we might be unable to ever satisfactorily gather evidence for it.
Supposing it is, it is no stretch for an artificial system to be sentient. And if such an A.I. is running on a distributed system over a network, it will be a colonial mind. And it may build a host of humanoid bodies for itself. This has appeared in literature in the form of the Geth people. Each Geth physical body is actually a server holding thousands to billions of minds that act like a colony.
If such a complex system exists due to distributed computation, there is little to no reason why a natural system could not evolve in a similar way. Again, literature presents this in a work of art: Arthur C. Clarke's Rama series of books has a species that is a sentient colonial fungus. This fungus sometimes lays "eggs" out of which come some furry creatures, which are its children in a solitary (i.e.: non-colonial) generation (just like some coelenterates have alternating generations). The solitary furry animals are the same species as the fungal colony and can telepathically commune with it, and act as the fungus's avatars.
Another instance of this is the fungus called Planet in Sid Meyer's Alpha Centauri. It covers the whole planet and absorbs other beings into both of its mass and conscience. Late in the story it joins with some humans in mind only, with the human bodies serving as Planet's avatars.