My own nomination - the discovery that really had me jumping up and down
when it appeared - was the announcement of the Vetulocystidae from the
Chinese Cambrian:
Oh yes, those are quite impressive animals. But I find their bad
preservation excruciating. Is the "posterior cone" the anus? Or does the gut
continue all the way through the "tail"? In the former case, what is the
"gut" in the "tail" -- perhaps even a notochord??? And the anterior cone...
<struck down by migraine>
Sorry that I supported the suggestion of *Dilong*, BTW. I instinctively
assumed that the most important dinosaur discovery of 2004 was meant.