Greenish Eggs and Dinosaurs

Oops! Zack's in trouble again! He buys a large, green, weird-looking egg at a flea market, then the housekeeper inadvertently does the exact thing she was told not to do: she microwaves it. Suddenly he's taking care of a very strange reptilian something. It might be a plesiosaur, it appears to be growing quickly, and one thing's for sure--it's not going to fit in Zack's small Manhattan apartment for long!