“isotopic analysis”
I missed finding out exactly what the definition of that was in my science class in grade school.
This is often done with teeth, since they tend to survive better in archaeological contexts, but bones work also.
https://freerepublic.com/focus/chat/4111817/posts
https://freerepublic.com/focus/chat/2597960/posts
https://search.brave.com/search?q=stable+isotopic+analysis&source=desktop&summary=1
Sounds like Carbon-14 , or similar.