How come animal become a supertype to dog and cat here. not even defined anywhere in code (like using constructor)

JavaScript
1 
type or paste code here
like

 function Dog ( ) { }

Dog.prototype {
constructor: Animal,
}

Though dog’s protype must be initialized with constructor: Dog, else constructor property will fail (instance of works ,still). Help me understand this. Break and give detailed explanation. God bless.

2

look at following challenges, here there is not yet the connection of Cat to Animal