WUHAN -- A collaborative study between Chinese and US scientists has revealed that horned dinosaurs experienced a decline in intelligence, hearing and sense of smell as they evolved to larger sizes over 100 million years.

The research, published recently in the journal Paleobiology, was conducted by scientists from the China University of Geosciences (CUG) in Wuhan, the Institute of Vertebrate Paleontology and Paleoanthropology under the Chinese Academy of Sciences, the George Washington University and other institutes.

Horned dinosaurs, or ceratopsians, are a group of herbivorous dinosaurs that lived in the Jurassic and Cretaceous periods. Early ceratopsians were small, bipedal dinosaurs measuring one to two meters in length. Over millions of years, they evolved into massive quadrupedal species, such as triceratops, that grew up to nine meters long. The physical and neurological changes accompanying this growth have long puzzled paleontologists.

By delving into the morphology of the cranial cavities of early ceratopsian dinosaurs, the scientists have shed light on the behavior of these ancient creatures.

Instead of the traditional method of creating a physical cast of the cranial cavity using materials like resin, the research team used computed tomography to scan the dinosaur skulls and digitally reconstruct models of their cranial cavities. They analyzed in detail the cranial structures of three early-diverging ceratopsians including the Late Jurassic Yinlong, and the Early Cretaceous Liaoceratops and Psittacosaurus.

The scientists inferred from their features, such as the attenuation of the semicircular canals and the heightening of the anterior semicircular canal, that early ceratopsians had more acute senses of hearing and smell than their later, larger counterparts.

They also found that the early horned dinosaurs bore relatively large brain volumes, even higher than most extant reptiles.

"These findings are interesting," said Han Fenglu, an associate professor at the CUG, delving into the question of why some organ functions deteriorated during ceratopsian evolution.

"It is most likely linked to their increasing body size," he said, explaining that smaller ceratopsians relied on sharp senses to evade predators, while larger species, equipped with substantial body mass and defensive bony horns, likely depended less on sensory acuity for survival.

The study also offers valuable insights into the broader principles of biological evolution, Han added.