What is the "mock turtle" as opposed to a regular turtle or the tortise? Is it not really a turtle?
You need to remember that you are reading a book full of satire and figurative language. The mock turtle is intended to be a representation of a turtle that is mocking his own society (the personification of a turtle vs. a tortoise - which one is wisest?) - remember the tortoise (taught us - in British dialect) and the other delectable puns throughout the story.
If you take a step back from Wonderland and gain the perspective of a visitor there of the insanity and backwards ways - it is almost looking at the society of Great Britain at the time of Carroll's creation.