Thirty-three reptiles were found dead last week at a Tennessee zoo, and officials there say they have no clues yet about how it happened.
Zoo Knoxville told local news outlets that nearly all of the dead animals were snakes. They were all found dead in the reptile area.
Surviving animals were removed and given oxygen.
Zoo officials have stopped using the reptile area for animals while the deaths are investigated, the AP reports.
Zoo Knoxville President and CEO Lisa New calls the deaths a "devastating and catastrophic loss."
Phil Colclough, the zoo's director of animal collections, says tests being conducted include checking for harmful gases in the building and for mechanical errors on thermostats.
"These animals were important ambassadors who helped so many people understand the role snakes and lizards play in the balance of nature," New said in a statement, per the Knoxville News Sentinel.