The Paleozoic era had many interesting animals in it. In the Cambrian, there were oddities such as Wiwaxia corrugata, Opibinia regalis, and is also when trilobites first appeared. Shortly after trilobites first appeared, so did the ammonoids. Then, in the Devonian, along came the fish; even the fish were odd, such as Dunkleosteus terreli, which looked like a fairly normal (albeit huge) fish, except for it's head. Dunkleosteus looked like it had grown a second skull on the outside of its head.
So anyway, the main way that we know about these animals is through fossils. Some, the cartilaginous fishes, are only known from fossil teeth, as cartilage doesn't fossilizes. Then there are ones preserved in near perfect detail, such as trilobites.
Here I have made 3 LEGO models of Paleozoic- era fossils (although it is intended as one set with 3 models). There is a trilobite, a eurypterid (aka sea scorpion), and an empty ammonoid shell. Each has its own stand shaped like a chunk of rock, as though they were actually fossilized into the stands.
I think that this would make a great set because it is a great display, it's educational, and it's accurate. I built it for fun.