A mini horse has been nicknamed the "BART pony" online after being photographed aboard a Bay Area Rapid Transit system train in California.

Twitter user @rodrlou made the miniature horse into a viral star when he snapped a photo of the equine aboard a commuter train Tuesday and branded it the "BART pony."

BART officials confirmed the mini horse boarded a BART train with its owner at the Rockridge Station in Oakland. The owner presented transit workers with paperwork showing the horse is registered as a service animal.

"The station agent consulted supervisors who called the legal department for advice," BART said in a statement provided to KNTV. "The legal department advised the agent to allow the horse and person in."