While Sunday saw the 58th anniversary of “Leave It To Beaver’s” first episode premiere, Monday there’s another “beav” in the news – one whose debut beat the Cleavers by about 166 million years. According to a new study published in the Zoological Journal of the Linnean Society, an ancient fossil belonging to a previously unknown species of beaver–like mammal has been discovered in northwestern New Mexico. 

Dubbed Kimbetopsalis simmonsae, the furry creature – which measured two to three feet long and weighed 22 to 66 pounds – originated some 100 million years before the extinction of the dinosaurs and would even go on to outlive the prehistoric creatures.

The discovery has given researchers a glimpse into how some mammal species survived and flourished after that giant asteroid struck what is now Mexico 66 million years ago.

Related: Giant prehistoric lizards co-existed with humans

“It seems like mammals that were smaller and had more generalist diets were better able to survive, probably because they were more flexible in where they could live and hide, and what they could eat,” researcher Steve Brusatte of the University of Edinburgh told FoxNews.com.  “And then these mammals found themselves in a brave new world barren of dinosaurs, and they began to explosively diversify after the dust cleared.”

The new mammal was a multituberculate­, a group of mammals that Brusatte describes as “basically primitive versions of rodents.” In fact, Kimbetopsalis and its ilk were very similar to modern rodents in their body sizes, diets, and behaviors. While it lacked the flat tail that beavers today have, Kimbetopsalis did have big, buck­–tooth incisors at the front of its snout. These ever–growing teeth were used to chomp down on plants and stems before huge molars with many rows of cusps ground the foliage up.

Whether or not they constructed and lived in dams, however, is unknown.

“They were plant-eating specialists, which is important because very few mammals that lived alongside the dinosaurs were dedicated herbivores,” Brusatte explained. “The new mammal lived only a few hundred thousand years after the dinosaurs went extinct, so it is prime evidence of how mammals were changing so quickly, and evolving new diets and lifestyles, so soon after the dinosaurs bit the dust.”

With no dinosaurs to hunt them or compete for food with, these primeval beaver–like creatures were free to spread through what is now Asia and North America, living in rivers, lakes, and forests. Then, around 35 million years ago, multituberculates were replaced by the rodent. Though the reasons for this are unknown, scientists suspect it may be due to the rodent’s intelligence, as well as its ability to grow faster and reproduce more quickly. These factors would give them a big advantage in competing for resources. Still, the multituberculates had a good run, surviving a giant asteroid’s impact and thriving for a good 120 million years.

Related: Mass grave of new human relative discovered in South Africa, claim scientists

According to Brusatte, the fossil was found by a student last year, and it wasn’t long until the team – led by Tom Williamson of the New Mexico Museum of Natural History and Science– knew they’d discovered a new species. Brusatte is anxious to return to New Mexico, where he hopes to learn more about that catastrophic event 66 million years ago.  

“We are trying to better understand what happened in the aftermath of the [dinosaur] extinction,” he said. “How did life change after that extreme moment of devastation?”