The oldest rhinoceros in the United States has died at a Tennessee zoo. Dolly was 56 years old. In a social media post Thursday, Zoo Knoxville said Dolly was euthanized after her mobility declined significantly in recent days despite receiving old-age medical care for some time.

Zoo Knoxville is mourning the loss of Dolly, a 56-year-old Southern white rhinoceros and the the oldest rhino in the United States, who was humanely euthanized following a decline in the rhinoceros’ mobility.