If you want to also dabble with more earth spells and more spell slots for actual summoning, going Arcane caster with Undead Master archetype is also an option. Otherwise, Undead Summoner is great if you're leaning more towards one big boney buddy and want the Archeologist dedication asap.
Old man robot has a point.
There are dinosaurs still alive on Golarion. Most other people wouldn't care that you've reanimated an ancient set of dinosaur bones vs a more recent one, only that you have animated undead.
I understand kind of the theme, but since dinosaurs are very much still alive on Golarion this is kind of analogous to the idea of going to Ancient Egypt and animating the bones of an ancient buried corpse. Sure you can do it. But people aren't going to care or know that the bones are ancient (necessarily). They're just going to see an undead monster.
It's also going to be hard to do for a GM, because they GM would have to figure out where you would have fossilized stuff. Like fossils don't form just everyone. There would have needed to be certain ground conditions in the place and time when the thing died. So depending on where you campaign takes place, there might not be any fossils in that region.