Sculpting details to clearly distinguish a lion from other large cats
Ultimately sculpting is as much about your ability to observe your subject as your  technical ability to manipulate the medium. 

It may help you to do some preparatory sketches. Unless you have a zoo or wildlife park near you you will probably be stuck with sketching from photos rather than life but you will certainly want to look at a range of material. 

You might want to look at two pictures of say a lion and a leopard side by side, ideally from similar angles as this will make the anatomical differences more obvious. 

The key here is to develop the ability to look at the details of your subject and put aside your prior knowledge of what you 'know' it looks like. 

One thing in particular which may help is to look at the proportions of your subject, this goes for both humans and animals. For a face you might want to look at things like, eye spacing and height, head length and width width of the nose etc etc.