OOPs-inheritance: Regarding creation of objects for inherited classes in java?

A child class is always supposed to have some extra features or methods. If java allow to store parent class object on child class reference, it´s expected that we can call child class method but we can´t. For example we have parent class Animal, and Dog class has one extra method bark() which animal class don´t have. Now if we see

Dog dog=new Animal();

dog is expected to call bark() but we can´t, Java supports run-time polymorphism and Animal class don´t have bark() implementation. Everything will be very confusing. On the other hand if we do like this:

Animal a=new Cat();
Animal b=new Dog();

and in this manner we can call all general methods and extra methods implemented in respective child classes and it shows the abstraction also.