A bizarre and tragic incident this week in which a young bison died in the Golden Gate Park paddock hours after at least one small dog was found in the enclosure has prompted the Recreation and Park Department to consider increasing signage about leash rules in the area.

A female dog walker has been cited and fined for violating municipal codes involving leash rules and animal disturbance, Rec and Park said. The historic paddock is marked by at least one sign saying dogs must be leashed, according to the department.

Necropsy results released Thursday revealed that the bison had extensive bruising on its left chest wall and sternum, and blood in the left chest cavity, according to the San Francisco Zoo, which takes care of the bison. The injuries were attributed to blunt force trauma, possibly due to running into a fence post or tree.

A witness, Greg Leonard, said he saw two dogs enter the paddock Wednesday morning and they began to chase the bison.

"They started running around where the buffalo were and so the buffalo just went kind of wild," Leonard told CBS 5. "They were running around and one of them injured itself."

An investigation is ongoing, but Rec and Park said a "toy breed" pooch entered the enclosure by burrowing underneath the fence. A zookeeper found one of the smaller bison with a laceration on its left side. An examination revealed three broken ribs, which were treated.

The 6- to 7-month-old, 600-pound bison was returned to the paddock, but found dead about 5:20 p.m. Wednesday, Rec and Park said.

Seven young female bison were brought to the paddock Dec. 6, Rec and Park officials said. Assemblywoman Fiona Ma helped bring the new bison to the park.

Ma said her staff is working closely with park officials to ensure no similar incidents occur in the future. A spokeswoman for Ma said the lawmaker does not have immediate plans for legislation, but would consider action if warranted by Rec and Park’s investigation.

Police arrived on the scene at 9 a.m. Wednesday and found the dog’s handler trying to coax the pooch out of the enclosure. She had with her a total of five unleashed dogs, officials said, and was cited and fined $307.

"This is an on-leash dog area, and this dog handler violated the regulation," Rec and Park spokeswoman Connie Chan said Thursday.

The paddock is located near an enclosed off-leash dog area. The paddock is lined with chain-link fence about 8 feet high. There are brown signs listing the rules at each of the four entrances to the off-leash area, including that dog handlers must carry one leash per pooch.

Two signs indicate dogs must be on a leash outside the dog park, around the bison paddock.

Nancy Stafford, co-director of the San Francisco Professional Dog Walkers Association, said it is rare for walkers to take pooches off their leashes where it is forbidden.

"I’m not condoning that, it’s just a reality," said Stafford.