Comments on: Getting a Handle on Theropod Arms

By: Matt

Matt — Tue, 24 Mar 2009 10:26:30 +0000

Any chance the therapod could have been ‘knuckle dragging’ or dragging its claws with the tops of the hands forward or angled toward the ground instead?

By: Michael Skrepnick

Michael Skrepnick — Sat, 07 Mar 2009 00:22:42 +0000

Jerry is correct, and I mentioned in my initial correspondence to Brian that eversion of the arm complex from the ribcage and rotation at the shoulder could accomplish the same result. I remember Paul Sereno discussing radius and ulna in early theropods essentially locked in place, and with a simple carpal block, pronation / supination would be virtually eliminated. . . not so sure in regard to more advance theropods though. While the skeletal elements themselves may remain relatively rigid, soft connective tissue, ligaments,cartilage, etc. . . may allow for a limited range of rotation, being a little more plastic at the joint articulations.
Further, just as another point of interest, I recall Phil Currie recounting (pers. comm.), that many of the Gorgosaurus specimens recovered from Dinosaur Provincial Park, with skeletal elements in articulation, noted that most were found with both manus ( mani ? )oriented so that the palmer surfaces were actually directed in an antero-medial ( or dorso medial, depending on long axis placement of the arms ) positioning. . . so unless this was some sort of post depositional artefact in preservation, it might be indicative of further mobility at the wrist, in this group.

By: Jerry D. Harris

Jerry D. Harris — Fri, 06 Mar 2009 20:00:30 +0000

But paleo-artist Michael Skrepnick reminded me of another trackway that confirmed the mobility of theropod hands.

Well, I don't agree that it necessarily shows anything about hand mobility, but it may say something about arm mobility. After all, birds can get their hands palms-down...but not by pronating at the wrist! Instead, it's an effect of abducting the arm from the body. The same may be true of the theropod that made the BC tracks. Perhaps a semantic issue (hand vs. arm), but a somewhat important one lest someone reading this thinks that theropods were capable of pronation/supination the way humans are (see also Zach Miller's excellent summary of this.)