Most of the ecological roles went to pseudosuchians, the croc-line archosaurs. Nor were dinosaurs especially diverse compared to the competition. Indeed, during the Triassic dinosaurs (especially the few large dinosaurs) were mostly limited to higher latitudes, because the deserts of Pangea’s tropics were simply too hot for them. Dinosaurs weren’t superior to other groups of animals around, and weren’t particularly well-suited for the Triassic compared to their contemporaries. The second, and perhaps more important, point is that the entire narrative of dinosaurs taking the world by storm, because they were supposedly better-adapted for the Triassic than other animals were, is just plain false (and studies were pointing this out as early as 1983, so BBC has no excuse). So Postosuchus would probably kill or subdue its prey on the spot like any other large predator. As for the depiction of it fatally wounding prey and then tracking it for hours on end, that’s another problem: this was based on the idea that some modern predators operate like this, but as it turns out the only predators that actually release and then track prey are vipers, which have potent venom to do their work for them. Even after being slowed down by the injury, it wouldn’t have been quite as slow as it was in the show. There is absolutely no reason that it couldn’t just chase down the Placerias or pounce on it after a short dash. On top of that, Postosuchus is one of several “rauisuchians” that are now known to be obligate bipeds: its forelimbs were actually too small to support its weight. Their leg proportions aren’t any worse than those of big cats today. “Rauisuchians” (in quotations because it’s now thought they aren’t a natural taxonomic group) weren’t the leggiest of animals, but all of them still had decently long limbs, as well as a fully upright stance. Regarding the first point, it makes absolutely no sense for Postosuchus to be as slow as it was in the show. There are two reasons for this: a misunderstanding of Postosuchus anatomy and movement, and then-outdated ideas about how dinosaurs became the rulers of the Mesozoic. This animal is the largest predator shown in Episode 1 of WWD (New Blood), and it, and the underlying narrative of the entire episode, is severely lacking. But they probably wouldn’t know it for what it really was. Anyone who has seen the original Walking With Dinosaurs series will know this animal.

Postosuchus walking with dinosaurs