I'm not necessarily saying that you have to see dinosaurs. I'm saying that you have access to CR 3 creatures, LIKE THIS.
Many DMs create custom creatures, or steal them from other resources. If your DM knows and understands the limitations of the Moon Druid (and he's the DM, so he should), he should recognize when the party should encounter new beasts so that your Wild Shape feature can grow.
That was one example. If you were DMing, would you say that a level 9 Druid SHOULDN'T have a CR 3 beast form?