When Nigel releases the Mononykus, the shot switches from the animatronic dinosaur model to a computer animated one. Nigel is holding the tail of the animatronic with his left hand, but then his hand suddenly moves to the head of the animal, as he pulls the bag off the animal's head with both hands.
Even though the Momonykus was correctly shown having feathers, the Velociraptors who appear in this program lack them. When the mini-series was made, there was already evidence that suggested they were covered at least partially in feathers, and other documentaries about dinosaurs got this right.
By the time this series was made, the theory that the dinosaur Velociraptor, as well as the episode's main feature, the Therizinosaurus were feathered had already been largely accepted (and later proven correct by fossil finds), so it is entirely unrealistic for this program to portray them with scales.
Saurolophus is shown with a thumb, but fossils show that these animals lacked thumbs.
Saurolophus is shown with a wide, spoon-like bill, but in reality, its bill was more triangular and thinner.
Velociraptor is shown slashing the Protoceratops' skin with its claws. Actually, raptor claws were unsuitable for slashing and making long cuts. They were more meant for climbing, holding onto things and puncturing, since they lacked a sharp edge.
Nigel's stick doesn't cast a shadow on the Protoceratops as he runs through their nesting ground.
The tree branch clearly clips into the head of the feeding Therizinosaurus.
Many times, the CGI animals don't disturb the plants and dirt on the ground and in certain shots, they don't have shadows.
As they walk, the tip of the Therizinosaurus' foot claws sometimes clip into the ground.
Nigel states that there are six-seven Velociraptors hunting the Protoceratops, but only four are ever shown.
Tarbosaurus and Velociraptor are not known to have coexisted. Tarbosaurus evolved about 5 million years after the timeframe of this episode.
Nigel says that one of the Velociraptors got injured when the Protoceratops snapped its arm with its beak. But it's only shown giving the Velociraptor a slight nudge with its closed beak. How was that enough to break its arm?