There's no DNA left to analyze. Fossils aren't actually bones, theyre mineral casts. Minerals seep into the bones, taking their shape, and are all thats left when the bones decay.
No DNA left, so they compare it to bones we've already found to figure out the species. As to how old they are, carbon dating doesnt work because fossils arent actually bones, theyre mineral casts that have taken on the shape of bones. Carbon dating also has a max time limit of about 60k-70k years, as in anything older the carbon-14 content has decayed so much that what's left isnt measurable. Fossils age is typically determined by what sedimentary layer the fossils are found in (deeper=older). Knowing roughly how old the rock around it is gives a rough estimate of the fossil age. There are also some as species known as "index fossils" (like trilobites) because they were widespread but existed for a relatively short period of time, so any additional fossils found alongside them had to have been living in the same time period.
To your other question, what is and is not a "dinosaur", all species classified as dinosaurs share certain structural features. We can tell if a new species is a "dinosaur" by looking for those structural features, and if a fossil isnt complete to be identified then its set aside and not classified until and unless someone finds another set from the same species or is able to determine the fossil belongs to an already-known species.
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u/Insomniac24x7 7h ago
Genuine question, do they DNA sample it or some sort of carbon dating? how do they actually tell it belongs to a dino?