In the wild turtles and lizards spent a lot of time basking in the sun. This is how they synthesize vitamin D.
If humans spend 20-30 minutes a day in the sun, Vitamin D supplements are not considered necessary unless you have a condition indicating otherwise. The more skin exposed, the less time needed for exposure.
Our snakes are consuming Bone, very high in Vitamin D, one of the necessary building blocks for bone.
I suspect (I don't know) that the white chalky part of the urates eliminated is mostly "bone waste". Maybe someone else will verify or shoot this theory down.
In humans, our bone is constantly being broken down and rebuilt. We drink enough water to filter this out unseen in our urine.
Sorry, more than most wanted to know, but maybe there are a few physiology nerds out there.
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