Starting in 15mm, Splintered Light Miniatures have a range of animals including terror birds, wolves, boars, komodo dragons and others. Oh, and Giant Weasels.
In 28mm, the beastie featured here is one of two packs available from Gary Hunt Miniatures in New Zealand (but priced in US Dollars). Very drool worthy.
Moving onto cavemen. No web site yet for Forge of Ice, but see TMP for details of their Primitive Tents.
And finally, if dino fans put their money where their mouth is then Wargames Fcatory may create some plastic figures for us, on the suggestions list so far are Tyrannosaurus Rex and Small Carnivorous Dinosaurs. I think I may do a little research and suggest a small herbivores pack to give those meat eaters something to chase other than foolhardy time travellers.