Comment on Ornitholestes by DrScottHartman
I'm really sure about Archaeopteryx, seeing as how I've personally spent hours examining the specimen in question (the Thermopolis Specimen). I'm only working from photographs and measurements on Ornitholestes, so I'm not as sure about the range of motion, but I suspect it can extend at least a bit more (though perhaps not to where it would be comfortable to carry around).
It's always possible that Archaeopteryx had secondarily reduced the size of the claw. Or perhaps whatever initial function they had (e.g. prey acquisition) soon led to a wide range of morphs as the toe was adapted to different lifestyles. As I think I mentioned in response to someone else, even some oviraptorids seem to show evidence of the toe proportions (shortened digit 2 with subequal 3 & 4), despite lacking the ability to hyperextend the second toe (and not having a scythe claw).
Another thing people may not be giving enough consideration to is how often theropods manipulated objects with their feet. As the hands became more incorporated into the wing (or reduced in some large theropods) pedal manipulation may have become more common...it certainly works for living theropods.
It's always possible that Archaeopteryx had secondarily reduced the size of the claw. Or perhaps whatever initial function they had (e.g. prey acquisition) soon led to a wide range of morphs as the toe was adapted to different lifestyles. As I think I mentioned in response to someone else, even some oviraptorids seem to show evidence of the toe proportions (shortened digit 2 with subequal 3 & 4), despite lacking the ability to hyperextend the second toe (and not having a scythe claw).
Another thing people may not be giving enough consideration to is how often theropods manipulated objects with their feet. As the hands became more incorporated into the wing (or reduced in some large theropods) pedal manipulation may have become more common...it certainly works for living theropods.
I know is comment is >3 years old, but regarding the foot manipulation part, does this include even theropods that lacked an opposable hallux (seems to be implied by your mention of large theropods with reduced hands)? Could their halluces still facilitate gripping even if not opposable?
Indeed, I had not thought much about foot-manipulation - then again, I feel most people have ignored theropod hands in general, leaving them hanging there like useless appendages, while evidence suggest otherwise - such as simply: Large hands. Even comparatively small hands, such as carnosaurid hands are still large, and clearly had to be used for something. In yet another un-scanned drawing of a megalosaurid, I wanted to add a subtle attention to that, by showing it curling its fingers inwards - instead of just leaving them hanging - so to suggest that it is moving and curling and stretching its fingers while walking, kindov like a bored person tapping fingers against the desk 
Lately I've also begun to imagine Tyrannosaurus mini-hands (which are remarkably well developed despite size) to be for communicative flapping I'm probably far from the only one with that suspicion, I'm sure!
Lately I've also begun to imagine Tyrannosaurus mini-hands (which are remarkably well developed despite size) to be for communicative flapping
I'm probably far from the only one with that suspicion, I'm sure!