I figured I'd want to ask fossil-related stuff, but I'm not sure if this would be within the purview of this SE site. Can I ask questions about, say, dinosaurs or pre-Holocene mammals?
It really depends on what you are asking. A question about dinosaur anatomy, mammoth embryology, or hominid evolution would fit pretty solidly in biology.
A question about carbon-dating methods, fossil preservation, or fossil bearing formations in would be pretty firmly in geology, and not biology.
Paleontology is a science that ignores our flawed attempts to classify science into discrete categories.