The female lion, 5-year-old Johari, was bitten on the neck by one of the male lions on Sunday afternoon, zoo officials said. Witnesses watched two lions approach Johari.
"The male lion that started it just had his mouth over her throat, and everyone thought they were playing at first," Michael Henshaw told Dallas television station WFAA. "But then they could see she was struggling."
Zoo staff members were seen throwing meat at the lions to try to distract them, and eventually security moved away witnesses and closed off a restaurant with windows overlooking the exhibit.
Lynn Kramer, the zoo's vice president of animal operations and welfare, says five lions in total are typically in the exhibit and have never appeared to endanger each other before. The three lions in question have been in the same exhibit for three years, Kramer said.
"I would have to think something caused the males to react that they don't normally see every day," he told The Dallas Morning News. "Lions can be aggressive, but they don't kill each other."
The zoo says the aggressive lions were not euthanized.