Found this in Nature a couple of weeks ago:
Palaeontology: Skull morphology of giant terror birds
Luis B. Chappe and Sara Bertelli
These monstrous birds were probably more agile and less portly than previously thought.
Here's part of figure 1:

Skull of the terror bird, Patagornis marshi
Hmm.... "Less portly?" I wonder....

Life reconstruction of "terror bird," with its hideous "death grimace."






