I was so curious about this (a great way to procrastinate from doing work I really need to do, too
) that I emailed the librarian at the Instituto Cervantes. He wrote back that he did not know of any animal that was officially a symbol of Spain, but he said that the
toro and the
lince ibérico would be the most representative. I'm not familiar with the iberian lynx, but of course I know the bull very well!