I can't detect up from down in this shot--is it supposed to be a dinosaur? Are those jaws? Sorry, but even with a calibrated monitor I can't tell what to home in on.
I think if you used a different point of view and the skull was completely on the photo it would've been better. now there's something at the bottom and a half skull at the top. the colors look nice, so I really think you could've got some more out of this.
I can't see excatly what you are photographing here. If it wasn't for your title, I wouldn't know that this was a fossil (assuming in a museum) I think the crop is too tight.
I bumped the photo up a point. Aside from the composition, teh sharpness is great. I like how you tried to shoot it from a different perspective.
I really couldn't get a handle on exactly what animal this is/was, which is a shame. Also the table it's mounted on was distracting from the fossil itself.
It is tough to determine the type of skull, but maybe you were going for that. would have like a little more light and maybe done in B&W. Like the angle though.