This is the part where I beg my readers for help, kind of like how I did back with Nyctosaurus and Dimorphodon. This time it's for therizinosaurs. I really appreciate all the comments in the previous post. But I now have plenty of other questions. Let's see what kind of answers I can get!
1) Plantigrade vs. Digigrade: Make your case(s), folks. Andrea Cau's post on the subject, and the supposed therizinosaurs footprints are very convincing. However, Qilong makes some good points, too. Honestly, I'm having a hard time drawing a plantigrade, standing therizinosaur. There's no "heel," for one thing. Plantigrade mammals have nice big heels, but dinosaurs didn't. And when you think about it, a giant, 40-foot, 3-ton, big-bellied herbivore walking around on two plantigrade feet makes about as much sense as that same animal walking around digigrade, forever risking toppling forward because the majority of its bulk is in front of its feet. I know that knuckle-walking isn't actually an option, but it almost seems like therizinosaurs should be quadrupeds somehow!
2) In all of your humble opinions, do you think the massive, grown-together pubis/ischium complex is indicative of a sitting habit, as is the case in chalicotheres?
3) Exactly how ridiculous should I make the back on a standing therizinosaurs? Many of the illustrations I've seen, including skeletals, show the dorsal vertebrae trending almost straight upwards in front of the pelvis. This is especially apparant in the most recent description of Nothronychus. It just doesn't look natural!
4) Given that therizinosaurs are basal maniraptors, do you think their arms and hands had the same amount of "folding" that, say, oviraptors and paravians demonstrate? Or better yet, did early representatives have that, like Falcarius, but later therizinosaurs lost it?
5) In more derived therizinosaurs, does the hallux actually contribute to the footprint? That is, are derived therizinosaurs actually four-toed?
6) The "feathers" of Beipaosaurus look a little bit like quills. Do you think that larger therizinosaurs would have retained some of these quill-like feathers, perhaps for intimidation? I can certainly see the advantages to ruffling up a bunch of quills and making yourself look larger and spiney!
That is all. Please post your thoughts in the comments! These animals have very strange skeletons!