Among Rhinos there is a popular idea that Long Ago, We lived for much longer than We do today. Maybe centuries or eons or millions. More than Three, at any rate. Rhinos simply have hazy concepts of longevity. It has never intrigued Us.
One theory is that Back Then and Whenever, there were vines that produced leaves that did the trick. Just munch on those, and you were good to go. On and on and on.
What became of those vines Rhinos cannot say. If We discover any of them, We will let you know.