At 21, Camilla Belle looks like a grown-up, dressed in a sleeveless gray sweater, jeans, black patent-leather boots, and the many rings and bracelets of a fledgling bohemian. You can tell she’s too mature to get wasted on tequila shots and flip off paparazzi, or to spout provocations to a journalist just to get a reaction. But adult as she may seem, right now all the girl in her wants to do is talk about puppies.

“Her name is Evolet,” she says. She’s referring to the miniature pinscher she and her parents, with whom she lives, got just after Christmas. The name was taken from her character in 10,000 B.C., the Roland Emmerich epic out this month. Belle is self-aware enough to know there’s something slightly embarrassing about this—the fact that just as her Evolet hits the screen, a furry little Evolet will be running around her house, peeing on newspaper. She quickly blames Mom. “My mother was obsessed with the name all through filming, and swore the next time we got a puppy . . . ” She trails off. Her mother, Cristina, who passed down to Belle the strong features and olive skin of her native Brazil, accompanies her daughter nearly everywhere, including to faraway film shoots; she spends most of this interview, which takes place at a trendy diner on Sunset Boulevard, circling the block in Belle’s Mini Cooper. “I’d forgotten how hard training a dog is,” Belle says. “Now I’m the mommy. I haven’t left the house in a week. My friends are all like, ‘What are you doing?’”

Belle’s been busy since infancy. She was scouted at a playgroup and went on to star in Subaru ads and play small parts in movies like Poison Ivy II. Three years ago, critics lauded her performance opposite Daniel Day-Lewis in The Ballad of Jack and Rose. Roles in the suburban satire The Chumscrubber, opposite Jamie Bell, and the teen thriller When a Stranger Calls, opposite a prop phone, followed. During that time, Belle also became something of a fashion-industry darling, appearing in Miu Miu ads and sitting in the front row at a Chanel show.

While her earlier roles garnered her notice and industry respect, 10,000 B.C. should give Belle a much higher profile—or at least some box-office bragging rights. She portrays the love interest of a young tribal leader, played by newcomer Steven Strait. “I loved her because she’s tough,” Belle says of the character. “She’s not just a damsel in distress. She’s constantly fighting back.” Most of 10,000 B.C. was shot on location; the filming stretched out over six months and took place in New Zealand, South Africa, and Namibia. There were blizzards, downpours, and sandstorms. “There were times when we were on a mountaintop in New Zealand and we’re hardly wearing anything when I thought, What am I doing here?” she says. Hair and makeup—which for Belle involved a relationship with a spray-tan wand she wasn’t sad to see end—commanded at least two hours a day.