A night at the Zoo

You are a security guard doing the night watch at the zoo. You discover the the animals look different at night, they transform into anthropomorphic creatures. Unbeknownst to the Zoo, in an attempt to make a new enclose look more exotic a stone was incorporated into the design. Each night this causes the animals to transform until the daytime when they change back to to their animal forms. Very much a "Night at the museum" inspired adventure