They are plastic models sculpted by Bob Naismith for the Carnage game by Holistic Design:
http://www.holistic-design.com/introCarnage.htmI picked up a starter set cheaply on eBay hoping to be able to use the lizard mounts (there were twelve of them in the starter set). I converted these because I don't like the new style Lizardmen and there weren't any saurus cavalry in the old style
. After some trial and error I found a way to mount the plastic saurus warriors on top of them. I quite like their look, they look sluggish and stupid, which suits Cold Ones well. They were one-pose models so I bent the necks and tails after heating for some more variation.