In 2008, a wild coyote boarded a train at the airport of Portland, Oregon and took a seat:
[...] but wildlife specialists removed and released it before the train took off.
Even so, the sneaky interloper is forever immortalized in a song: Sleater-Kinney's "Light-Rail Coyote."
It was one of five animals known to have used public transit to get around, including a pigeon, a goat, a cat and a monkey. You can read about them at the link.