Fossils aren't bone. They're mineral deposits in the space the bone used to be. In rare cases there might be some original tissue but for the most part fossils are formed from sediment(?) infill. Preserved bones are...bones and not fossils. Think of fossilization like lost-wax casting.
Excellent point. I hadn't thought of it, but knew it as a kid, when I read your comment.
Do we know much about osteoporosis outside of humans, let alone dinosaurs? Seems to be a bit of a jump.
AFAIK bone loss occurs with age in both men and women, but accelerates for women after menopause. But did female dinosaurs have something like menopause?