The fossil which is approximately 250 million years old was found near the village of Poreba in Jura Krakowsko Czestochowska Mountains 200 km (124 miles) south of Warsaw, according to Dr Sulej. Scientists in China have discovered a nearly complete skeleton of the oldest ancestor of the long-lived mammal lineage. The fossil belongs to a 160 million-year-old creature known as the "Jurassic rat," one of evolution's most successful mammals.
Dubbed as "Rugosodon eurasiaticus," the newly discovered species resembles a small rat or a chipmunk. It was an early member of the group of mammals known as multituberculates, which flourished across the planet around 170 million to 35 million years ago during the Cretaceous era. Eventually, multituberculates occupied a diverse range of habitats for more than 100 million years before they were out-competed by more modern rodents.
The creature, which was unearthed by Chong-Xi Yuan from the Chinese Academy of Geological Sciences in Beijing and colleagues, contained teeth which were adapted to gnawing plants and animals alike. Researchers suggest that R eurasiaticus paved the way for later plant-eating and tree-dwelling mammals. Scientists also say that the fossil of the extinct rodent-like creature can also help explain how multituberculates achieved their dominance.
"The new mammal is called Rugosodon after the rugose teeth ornamented by numerous tiny ridges, grooves and pits, indicating that it was an omnivore that fed on leaves and seeds of ferns and gymnosperm plants, plus worms and insects," an international team of scientists from Chinese Academy of Geological Sciences, Beijing Museum of Natural History and the University of Chicago said.
The researchers described Rugosodon's ankle bones as being "surprisingly mobile and flexible", which suggests Rugosodon was a fast-running and agile mammal. "The later multituberculates of the Cretaceous era and the Paleocene Epoch are extremely functionally diverse, some could jump, some could burrow, others could climb trees and many more lived on the ground. The tree-climbing multituberculates and the jumping multituberculates had the most interesting ankle bones, capable of 'hyper-back-rotation' of the hind feet," said ZheXi Luo, professor at the University of Chicago. The researchers also said Rugosodon was a nocturnal mammal which lived in a temperate climate in lakeshores of what is now known as Jianchang county of Liaoning province in China.