When beached, the Liopleurodon looks about half the size it is supposed to be.
When the Rhamphorhynchus is plucking insect larvae from the tree, the animatronic head looks much bigger in comparison to the tree bark than the head of the CG animation.
When the animatronic Liopleurodon is replaced by a CGI creature mid-shot, the skin patterns on the side of its neck noticeably shift position.
In the final scene when the Eustreptospondylus find the beached Liopleurodon, a patch of grass-like greenery can be spotted in a shot. Grass hasn't evolved in the time this story takes place.
The narrator claims that the Ophthalmosaurus' jaws are toothless, but we see they have many, many teeth. The visuals are in this case correct: these animals really did have lots of pointy teeth.
The narrator states that Liopleurodon can grow up to 25 m long and weighs 150 tons. In reality, no Liopleurodon larger than 7 m has ever been found, and it probably weighed less than 10 tons.
Eustreptospondylus is described as an island-dwelling dinosaur that specializes in scavenging while swimming from one island to the next. There is in reality no scientific support for this idea. While the dinosaur was indeed discovered in marine deposits, none of its anatomical features support such a life style, and it is more likely that the animal or its corpse was simply washed into the sea, rather than having actually lived there.
When the Ophthalmosaurus is giving birth, it is evident that the animatronic used in this scene is being damaged by the water - bits of "skin" are falling off, revealing whitish rubber underneath.
In one shot, when one of the Cryptoclidus splashes into the sea, there is a puddle of water under its belly - and it shows no reflection of the animal.
As the Rhamphorhynchus are eating the horseshoe crab eggs on the shore, watch the one closest to the screen: the shadow of it's head is rendered wrong, and doesn't accurately mimic the movements the head makes. When the tip of its beak touches the ground, its shadow doesn't come closer.
In the closeup shot of the mother Ophthalmosaurus' eye, you can notice how the rubber around the eye is slowly coming off.
After the Cryptoclidus plunge into the water, they briefly become see-through.
In the final shot of the episode, as the young Ophthalmosaurus swim away, the camera buckles a bit, but the animals keep moving as if the camera were still.
Eustreptospondylus was already extinct by the Late Jurassic, which is the period this episode takes place in.
As the Eustreptospondylus hustle over the remains of the sea turtle, you can briefly notice the leg of the puppeteer on the right side of the screen, during one of the closeups of the animal's head.
In the opening shot in which we see the head of a Eustreptospondlyus through the water, a dark object can be seen above its neck at certain points.
When the Eustreptospondylus lifts up the dead Rhamphorhynchus, what seems to be part of the puppeteer's clothing can very briefly be glimpsed.
When the Ophthalmosaurus is struggling to give birth and breathe air, a red object can be seen behind her in one above-water shot.
Large attachments visible on the Ophthalmosaurus prop's belly when it catches a squid.
In the opening scene, the Liopleurodon doesn't beach despite coming very close to shore. An animal of that size would most likely have been caught up on the shore in the shallow sea. The scene was based on the behavior of modern-day orca whales, but according to the show, Liopleurodon was significantly bigger, so it would definitely not have adopted a similar hunting technique.
The narrator says the female Liopleurodon has serious wounds on its back flipper that the male's bitten into. But the animation doesn't indicate this, its flipper is shown to be perfectly fine.