There were two almost complete sets of skull rat fossils that were found in South America. One adult fossil and one baby fossil of two rodents were discovered and it has changed the whole perception of rats.

The studies suggested that the almost complete set of skull and a jaw from mother-baby giant rodents that were found in South America are the most well-preserved fossils of that species. Before, there were only tooth and skull parts of rodents that were dug.

According to Live Science, the fossils show that the rodents weight almost one ton, larger than most animals and rodents nowadays. This discovery might be debunked many known facts about family tree and genus of animals. Some animals that were thought to be in the same family might not be and some animals that are thought to be in different one might be the same, scientists stated.

During the Miocene epoch, many large rodents are roaming freely around South America. That period lasted for 23 million years to 5.3 million years ago. The biggest rat was Josephoartigasia monesi. It was as big as a buffalo and can bite as powerful as a tiger's bite, according to a study published in February 2016 in the Journal of Anatomy.

Because of those, there were proposed things to changed, like the juvenile members of the subfamily Gyriabrinae might be related to other subfamilies of Dinomyidae. Also, the three known species of the genus Isostylomys should be merged into just one species Isostylomys laurillardi, reported Science Daily.

"Our study shows how the world's largest fossil rodents grow and we describe fossil remains of a giant rodent baby and an adult. Comparing them we conclude that from very young the giant rodents already were very similar to the adults which allow us to deduce that the great majority of the hypotheses before posted were wrong, author of the study Andres Rinderknecht commented. 

The young and the old fossils observed in the study represent some of the biggest rodents science have encountered, Rinderknecht added. The newly discovered fossils were as big as this Capybaras.