I think the list below is compelling, some of them just don’t exist in the marketplace, but it would be more compelling having a male, female and baby versions for each species, you could sell sets of those instead of a huge pack with tons at once:
- elephant (adult and infant without fangs)
- ram (because of horns)
- koala
- panda
- kangaroo
- jaguar or leopard or cheetah (maybe all)
- hawk (with nest, eggs and newborn hawks)
- bull, cow
- mammoth
- zebra
- gnus
- antelopes
- several types of snakes
You could also have them separate by habitat or something related to species classification. Habitat is compelling since you can build an entire scene and sell it aswel.