Very nice work I am enjoying looking at your different sculpts, I use epoxy clay to sculpt as well. By the colour I am guessing you are using Apoxie is that correct? I have tried that brand but I found Magic Sculpt gave me better results for detail work.
On the Iquanodon as well as beefing up the ankles as has been suggested if you can get a hold of this paper. Wright, J. L. (1999). "Ichnological evidence for the use of the forelimb in iguanodontians". In Unwin, David M. Cretaceous Fossil Vertebrates. Special Papers in Palaeontology 60. Palaeontological Association, pp. 209–219. ISBN 0-901702-67-6.
Wright concluded by examining trackways ascribed to Iguanodontids "that when walking quadrupedally , iguanodontids, at least occasionally, placed their hands on the ground outside the line of tracks made by their feet, with the dorsal surface of the manus facing outwards parallel to the trackway midline."
All you need to do is turn the lower arm outwards to achieve that pose, if you wish.