It was a real jungle at the Dallas Zoo for annual Dollar Day.
Dallas police even had to put would-be patrons in a holding pattern after the parking lots completely filled up by late morning. Officers let in one car at a time as people finished up their zoo visit and left. Police also shut down the Ewing and Marsalis avenues exits off northbound Interstate 35-E.
Dollar Day is the annual event that lets folks into the zoo for only a dollar. It wasn't surprising to see full lots -- almost every year, massive lines block portions of Interstate 35. But at that early in the day? Wow.
The new Giants of the Savanna exhibit probably had something to do with it (click here for our photos of the exhibit), plus families love a good deal during these hot summer months.
Tens of thousands of people clocked in at the zoo, even in blistering heat that felt like 108 degrees. By 2 p.m., nearly 22,000 people had taken advantage of Dollar Day.
The Sharon family decided to get to the Dallas Zoo early Thursday morning.
"The weatherman said it's going to be a hot one, so you figure you come early -- that way they can beat the heat," Bill Sharon said.
And there were plenty of ways to beat the heat.
"Even coming in, they had a little stand where they were giving out free water," one zoo goer said.
"As long as they have these good mist fans and we can get a chance to stop occasionally, it's fine," Teressa Roberts said.
Indoor exhibits also pumped plenty of air-conditioning.
"We would see two or three, four animals, and then we'd make our way back to a cool area because they're spread out," Amanda Sharon said.
Some families didn't take any chances and brought along reinforcements.
"My wife wanted to make sure that we packed an ice chest with drinks -- juice for the kids, water for the adults," Simon Arenas said.
Families such as his were glad they did. Some concession stands ran out of refreshments fast, overwhelmed by the demand.
"We're out of basically ice cream, water," the zoo's Felton Turnete said.
It all left some wishing they had gotten to the zoo before the heat did.
"We should have been here at six," Roberts said.
The Dallas Zoo said 27,189 people attended Dollar Day, the second-highest attendance record.
The all-time record is 34,000 patrons, back in 2008.
Zoo officials said they think visitors stayed in the park longer than patrons did in 2008, when the weather was in the 80s, which is why they couldn't get more people in.
NBC DFW's Greg Janda and Shane Allen contributed to this report.