We all know that animal care-taking games are more than well-represented on the iOS charts. So is there still room for innovation in between all of those zoo games?

It looks like NaturalMotion — a U.K. company that started out building realistic simulations of human movement and then later moved into gaming — may have found the sweet spot. Its title My Horse, a simulation game where players take care of and feed a very realistic horse, appeals to the same demographic and has become a quiet hit with a half-million daily active users, the company tells us.

“We’re seeing more than 2 million daily sessions. This is an incredible sign for us as we have barely spent anything on user acquisition,” the company’s chief executive Torsten Reil tells us. Being Apple’s Game of the Week certainly helped, allowing the title to hover between #60 and #140 on the U.S. grossing charts for the last month.

Oxford, U.K.-based NaturalMotion started out building technology that realistically simulates human movement. Reil, who was working on a Ph.D. in biology (or rather complex systems) at Oxford University, studied how humans and animals moved. (You can see a TED talk from him here.)

“We had to understand the biodynamics. This is different from animation where you pre-record everything and play it back at the appropriate time,” he said. “The movement our technology supports is all generated on the fly. It allows us to create a living, breathing world where every time you play the game, something different happens.”

His company then went on the license that technology out to companies like Rockstar Games, which used it in Grand Theft Auto 4 and movies like Troy, which starred Brad Pitt.

When it became apparent that iPhones, iPads and Android devices were going to be formidable platforms in their own right, NaturalMotion started a gaming division to create original content.

They had a few initial titles like the football game Backbreaker, in which players run a football player down the field and try to avoid defenders until they get to the end zone and score a touchdown. It went on to do 5.5 million downloads.

Their most recent one, My Horse, was built with MunkyFun, a San Francisco-based studio headed by LucasArts’ former director of game technology Nick Pavis.

My Horse was NaturalMotion’s big experiment in doing freemium gaming. It contains all sorts of virtual items players can buy like special saddles for their horses and there are time-based mechanics familiar to anyone who has played a resource management game. Players can feed and groom their horses, getting experience points in exchange. There’s is also a competition mode, where players can have their horses do show-jumping.

What differentiates My Horse from the many other animal-related games dominating the top grossing charts is the sheer quality level of the art.

Most of the other animal-related games remain 2D and that has worked to date. But it’s slowly changing. Pocket Gems’ huge hit Tap Zoo was able to maintain a consistent Top #10 ranking for most of the year, but then similar games with slightly higher production quality like Backflip Studios’ Dragonvale began to surpass it.

Reil is betting this trend of rising art quality will continue and that NaturalMotion’s games will stand out against this backdrop.

“We see it in the world of animation where we shifted from movies like Snow White to ones like Toy Story now,” he said, pointing out that many of Disney’s biggest hits are now 3D and come from Pixar.

Unlike NaturalMotion’s console and film work, the mobile games the company builds are not to showcase the technology for third-party developers.

“Our games business is a business in its own right,” Reil said. “We know how to use our technology so we come up with concepts internally and then work with other firms. Having third parties come to us is not something we’re doing at the moment.” He says the company is aiming to have six titles out in the next 12 months.

NaturalMotion has a little more than 100 people and has taken an undisclosed amount of funding from Balderton Capital, which was Benchmark Europe at the time the round was announced. Reil recently moved to San Francisco and is trying to build a local office of about 20 to 30 people.