According to a 2016 study in Frontiers in Neuroscience, "the most reliable non-human beatkeeper to date" is a California sea lion named Ronan, who is known to bob in time along with music played by her trainers. She's not the first non-human to demonstrate a sense of rhythm: a cockatoo named Snowball has proven what scientists call "rhythmic entrainment to music," as have several Asian elephants and a chimpanzee. Scientists once believed that beat-keeping was tied to vocal mimicry, since to copy another animal's call you need to match not only sound, but timing too. But because chimps and sea lions aren't thought to be "vocal learners," their unique abilities put that theory into question.
Related: Music Gets The Dopamine Flowing