CHERTSEY, England — Dinosaurs can be challenging co-stars. Especially when you can't see them.

"Basically it's a man in a very colorful jumpsuit with something attached to a long pole going, 'It's swooping, it's swooping, it's coming around, it's coming down. Araaagh!' " says Ben Miller, mimicking an on-set stand-in for the beasts, later to be fully realized by computergenerated special effects.

As Sir James Lester, an arrogant government official, Miller only occasionally encounters a dinosaur. But the rest of the cast of BBC America's "Primeval" continually meet up with the fiercest of the species — or cozy up to the cutest.

"At first when you are reacting to a traffic cone on a stick it's a bit hilarious. The hardest thing was not to laugh," says Andrew-Lee Potts, who plays dinosaur-obsessed computer geek Connor Temple.

"It was a learning curve for all of us and there were a lot of giggles along the way," Potts added. "But now when you see new characters come to the show and you see those actors struggle with it, you realize how it's become part of your life, so I don't find it tough any more."

The series, which premieres tomorrow, is built around the adventures of a group of scientists turned action heroes. Attached to the so-called Anomaly Research Centre, they're investigating the sightings of alarming and intriguing creatures, which pop up in modern life via time warp holes in the universe.

"Primeval," which airs in Britain on ITV, is the creation of Tim Haines and Adrian Hodges.

A science journalist turned filmmaker, Haines produced the Emmy-winning BBC documentary series "Walking with Dinosaurs," a huge hit when it aired on the Discovery Channel in 2000. He also used similar CGI, animatronics and location footage to create plausible images of extinct creatures in the 2001 series "Walking with Beasts" and "Walking with Monsters" in 2005.

"It gave me a skill set where you say, 'Well, what else can this do?"' says Haines.

So he devised this TV drama with "a creature of the week" — often scary, but never so ghastly that it oversteps the bounds of family-friendly programming.

Haines explains that most of the creatures are drawn from historic truth because "if you obey the rules and design a creature based on biology or something that did exist, then people go, 'Oooh, that looks real!' "

Yet the fantasy element of the show provides license to let the imagination soar. "It's a fantastic relief not to have to worry about the length of their teeth and the size of nostril hair," Haines notes, "so I could add an extra sabre tooth to the Gorgonopsid and no one cared, because this is drama."

Besides the huge, predatory dinos, the show also features a harmless Scutosaurus, which looks like an elephant but is actually related to a turtle. On a smaller scale, there's Rex, a domesticated flying lizard. There are also giant spiders, millipedes, scorpions, worms, cute but deadly Dodos, the alligator-like Mosasaur, and a flying Pteranodon, which invades a golf course.

Because "Primeval's" time warps include the future, there is also the strange, ape-like and skull-headed Future Predator. It was the trickiest of the show's creatures to create because it is entirely imaginary. Bringing it from idea to screen took about three months.

"When effects step out of the background and become an active participant among the characters, that changes the dynamic, alters the drama. That gives you something audiences hadn't seen before," says Haines.

He notes there are still very few TV shows with such integrated effects: "If you look at space operas, they show flying machines and occasionally people walk on in a pair of rubber ears. Personally I think the age of rubber ears is over. What you need to do is to produce believable digital characters."

"Primeval" does that, but Haines is also quick to credit scriptwriter Hodges, "because I can stick as many monsters in front of you as I like, but un-less you fell for the characters, the team, you would not be interested."