The lead already says the first description of it's external appearance appeared in 2012. Perhaps I could add "published" in there somewhere to make it clear. Still not sure how to reread what you were referring to above:
 
"Until 2012, nothing was known about this species other than cranial and dental anatomy."

Again, to be clear, we could add "published about its external appearance"? Or is that too wordy? Or maybe reword the sentence altogether. What do you think?