The underwater shot of Hesperornis chasing schools of fish is recycled from Cruel Sea (1999), only with different computer-generated animals this time. Originally, it was footage of real life penguins chasing fish, where the penguins were digitally removed and replaced with prehistoric animals.
Like the original series, this spin-off also incorrectly asserts that the marine reptile Liopleurodon could grow to 25 m in length, making it the largest predator in the history of Earth. In reality, no specimen bigger than 6.5 m has ever been found, and even its larger relatives were "only" about 10-11 m long.
According to the BBC website, the small and large mosasaurs are called Halisaurus and Hainosaurus, respectively. Hainosaurus has since been reclassified as a species of Tylosaurus.
There is no evidence of skull horns in Hybodus.