Correct to the fossilized fragments I studied to make this that are over 400 million years old. Starting in the Carboniferous Era, before there were dinosaurs, Calamites gradually seemed to take over and filled the niche that grass does today. They grew all the way to the end of the dinosaurs. Here's a tip for your T-rex scene-there was NO grass on the ground. It is possible, though, that T-rex could have trampled ferns and calamites among other plants. The model itself is best in .3ds format and needs a good 'smooth-over.' It is also well suited for the overgrown giant calamites that rimmed the brackish swamps of the Carboniferous Era.