During the introductory scene, in the closeup shot of Halftooth's animatronic head bellowing at the terror birds, there is a hairy piece of dirt on one of his teeth. In the next shot, which is computer-animated, his teeth are clean.
Phorusrhacos was already extinct several million years before the timeframe of this episode. (The bird featured in the episode is actually its relative, Titanis. But since it is constantly referred to as Phorosrhacos, even in the book, this is a legitimate error.)
The carapace of the Doedicurus visibly bends at the front when it's being menaced by the young Smilodons, but its carapace was fairly solid in reality and attached to the pelvis, so it wouldn't have moved together with its upper body.