Add a so-called "BART pony" to the list of things that have caught the attention of riders and social media when it comes to the Bay Area Rapid Transit system.

On Tuesday afternoon, the animal was spotted on a train and started making its rounds on social media with riders posting photos.

BART officials confirmed the animal, a mini horse, came in with its owner at the Rockridge Station in Oakland. The owner showed paper work that stated the horse is a service animal, officials said.

"The station agent consulted supervisors who called the legal department for advice," BART said in an e-mail to NBC Bay Area. "The legal department advised the agent to allow the horse and person in."