I might suggest sketching on paper the antelope skull you'd like to pixel before actually pixelling it - the brain has this funny habit of misinterpreting the actual proportions of things, drawing what we 'think' we see as opposed to what we actually do.
I can't actually tell which skull from the link you're trying to do - none of the ones I see there have the same 'm' shaped horn, and I'm not edumacated enough to know which is an antelope (they all seem antelopey, except for the big ones that look like rams).
You might even like to borrow colours from the photo, too - as is, the skull to me looks like a flatter fossilized version thereof.