I made it to round 70 with nothing but Spiders and Bears. More details below.
I believe I could have survived a lot longer because the waves didn't seem to be getting much harder after a point, and I only lost to a round of enemy Spiders because I got careless and those guys are quick af. Spiders and deploying them right were the backbone of the strategy. They can take care of the lizards (just summon them on top of them and the lizards kill themselves) and high attack or venom animals because they have favorable trades with all of them, and the bears can take care of rats/wolves and other bears as the Spiders flank from behind and tear them apart. Besides upgrading your hand size which seems compulsory for any strategy, I only bought Spiders and Bears.
TL;DR: Bear tanks, Spiders do DPS and general fighting.