Pareiasaurs ruled the planet long before the dinosaurs. In the scientific community, these heavy-weight herbivores are known as the 'ugliest fossil reptiles' ever found.

Pareiasaurs once roamed Russia, Germany, Scotland in Europe, China in Asia, South Africa and South America. However, earlier studies didn't reveal if the pareiasaur groups were distinct in each region.

Now, palaeontologist Professor Mike Benton from the University of Bristol has found that the pareiasaurs fossils found China shared several similarities to those discovered in South Africa and Russia. Findings suggested that these heavy-weight vegetarians traveled across the globe notwithstanding their awkward movement.

Pareiasaurs measured two to three meters or about six to nine feet in length. They had huge, barrel-shaped bodies with short and chunky arms and legs. But despite their massive bodies, they had small heads and small teeth. Bony knobs covered their entire body and face as well.

To date, there are six pareiasaurs species found in China, most of which were unearthed from Permian rocks in the Yellow River banks. Benton analyzed the pareiasaurs specimens from various museums in Beijing.

He also traveled to the areas where the specimens were discovered. Based on his research, there were three pareiasaurs species that lived between 1 and 2 million years.

To date, there are no fossilized pareiasaurs feces found but these ugly herbivores most likely lived in damp lowlands where they fed on low-nutrition shrubbery. A past research found the evidence that pareiasaurs rolled in soft mud, which was most likely their way to keep parasites off and cool off.

"My study of the evolution of pareiasaurs shows that the Chinese species are closely related to relatives from Russia and South Africa. Despite their size and probably slow-moving habits, they could walk all over the world. We see the same sequence of two or three forms worldwide, and there is no evidence that China, or any other region, was isolated at that time," said Benton whose study found that the three pareiasaur species in China were different from each other in terms of teeth shapes and body size.

The pareiasaur species in China were part of the end-Permian, mass extinction that took place approximately 252 million years ago. During this time, about 90 percent of the species were wiped out by the devastating volcanic eruptions in Russia alone that caused global warming and acid rain.

"We can use this information as a basis for understanding how pareiasaurs migrated and colonized different parts of the world," said Royal Ontario Museum's curator of natural history Linda Tsuji, who was not part of Benton's study.

The new investigation was published in the journal Zoological Journal of the Linnean Society on Feb. 19.