A new study suggests that the biggest dinosaurs had relatively smaller brains.

Researchers examined the fossilized skull of a 70 million-year-old giant dinosaur Ampelosaurus - discovered in Cuenca, Spain, in the year 2007.

Ampelosaurus was a member of titanosaurs, a diverse group of sauropod dinosaurs. Sauropods are a subgroup of the saurischian, or "lizard-hipped" dinosaurs. The dinosaurs belonging to this group were the largest animals ever to have roamed the Earth. Many of the titanosaurian dinosaurs had armor-like scales that covered their bodies.

The research team scanned the interior of the Ampelosaurus skull using CT imaging and then developed a 3-D reconstruction of the dinosaur's brain. They found that the brain was not much bigger than a tennis ball. "We don't see much expansion of brain size in this group of animals as they go through time, unlike a lot of mammalian and bird groups, where you see increases in brain size over time," researcher Lawrence Witmer, an anatomist and paleontologist at Ohio University, told LiveScience. "They apparently hit on something and stuck with it - expansion of brain size over time wasn't a major focus of theirs."

Besides a smaller brain, researchers also noticed that the Ampelosaurus possessed a small inner ear, which is responsible for hearing. This suggests that the dinosaur was not good at hearing air-borne sounds. Researchers assume that the Ampelosaurus might have used a kind of hearing, wherein it depended on sounds through ground, the LiveScience report said. They suggest that the sauropod dinosaur was a slow-moving, herbivorous animal rather than being a dinosaur with rapid movements.

Researchers are currently deliberating on the neck posture of the sauropods - whether they held their heads down and grazed the ground vegetation or fed on high leaves like giraffes. Witmer believes that the inner ear of the animal could help in knowing about the neck position.

The findings of the study appear in the journal PLOS ONE.