Rather frustratingly, they disappeared from the North Star web site just as I was about to start buying the prehistoric ranges. I've made some inquiries since they disappeared, and it seems that the moulds now belong to the editor of Wargames Illustrated.
I've written to him requesting that the figures be re-released, but one letter isn't likely to make much difference. If you have an interest in this sort of figure, especially if you might actually buy, please consider writing a polite letter asking for the ranges to be brought back on the market.
In the meantime, if you want dinosaur figures, the best place to look is The Honourable Lead Boiler Suit Company. I can't say enough nice things about HLBS, their customer service is great.