Mysterious Palm

See that plant? The palm-like growth? It mysteriously appeared in my front yard at the beginning of the summer. I have no idea what it is, or how big it will get. I'm thinking it may have originated from a seed sent from my mother-in-law to my son as a souvenir from her vacation to Jamaica. The child insists he did not plant it there, however I do recall him asking me at some point if I thought it could still grow.
It has already grown about three feet, as you can see if it is going to get large, its placement is not ideal - it would be blocking my front door. So, can someone help me identify it? You may not be able to tell from the pictures, but it also has sharp teeth-like thorny growths along the edges of the stalks of the "leaves".