Other mammals are sentient, but not sapient so far as we know, with the possible exception of some species of dolphins and whales, but this has yet to be proven. (It is pretty much proven that apes, monkeys, etc are not sapient)

What’s they key distinguisher of sapience? There are different measures, but “theory of mind” is the one that seems most relevant. The ability to think about what someone else is thinking. This seems to correlate also with the ability to ask questions and tell stories, and we currently know of no other being besides humans that can do either— again, research into dolphins and whales continues, and there might be potential there, but we’re pretty darn certain nothing on land has it.