WMG: Prehistoric Park

The park is responsible for the events of Primeval
Obviously something went wrong with the time portal device, causing the anomalies. This would explain why they look similar and why most of the anomalies lead to prehistoric times.

They did end up messing with the timeline

Hence why Ornithomimus is a filter feeder without feathers and all the other inaccuracies.

The whole thing started because of "Sea Monsters"
Remember the Pteranodon Nigel tamed in that special? After the mosasaur attack, he brought it into the future with him and set up a zoo enclosure for it. He was so inspired from this, that he decided to do this with more prehistoric creatures.