What is a Groundhog?

Why do groundhogs have they're own day?

If they are rodents, then why no long tail?

Maybe they are in the capybara family of gigantic rodents in South America.

Maybe they mutated from the rat family (rattus rattus) in an evolutionary push to spend more time carefully meditating on their shadows!


If they have their own day, is the shadow a problem only in Punxsutawney?
What if it's raining in Punxsutawney and sunny in Manteca?

It's a puzzle to me.
I've always wondered about this.
I'm wondering, please advise.