These Ancient Mammals Thrived After The Dinosaurs Were Wiped Out

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Justine Alford

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2741 These Ancient Mammals Thrived After The Dinosaurs Were Wiped Out
Kimbetopsalis simmonsae/University of Nebraska-Lincoln

The K-T extinction event was spectacularly catastrophic for the vast majority of Earth’s inhabitants. Thought to be driven by a lethal asteroid/volcanic activity combo, it brought dinosaurs, alongside pretty much all of the other large vertebrates, to their sorry end, and of course most plants, too. But it wasn’t all bad – shoving the big’uns out of the way allowed other, smaller species that survived to thrive. Like this newly discovered mammal, or “prehistoric beaver” as some are nicknaming it (it’s not a beaver).

Found by an undergraduate student at the University of Nebraska-Lincoln just a few days into her first fossil hunt, not bad for a novice, the previously unknown species is a type of multituberculate. First appearing some 165 million years ago, these rodent-like mammals are completely extinct now, making them the only major mammalian branch to have become so.


But while they have left no living descendants, they were very successful animals for a significant period of time, scuttling around for 130 million years. Part of that achievement is thought to be owed to their omnivorous diet; happily munching away on greens or meat meant that food availability was not such an issue as for those with more specialized diets. That said, the largest of the multituberculates – taeniolabidoidea – had teeth that were adapted for chomping on vegetation, and that’s what stood out for the researchers behind this new find.

Describing the discovery in the Zoological Journal of the Linnean Society, the species description is based on just a few fossilized remains: jaws complete with molars and premolars, alongside front incisors and a fragment of the skull. They were found in the San Juan Basin, New Mexico, marking the first multituberculate to be found in the area for more than a century.

Newly discovered teeth. University of Nebraska-Lincoln

When the discoverer, student Carissa Raymond, brought her supervisor Thomas Williamson the strange looking black teeth she found poking out of the grit, it didn’t take long for the exploratory team to work out they were on to something exciting. They noticed the characteristic multituberculate dentition which kind of looks like ears of corn, but also blade-like teeth specialized for hacking away at vegetation. It is these that partly served as inspiration for the name, Kimbetopsalis simmonsae, with psalis meaning “cutting shears,” lead researcher Dr Stephen Brusatte told BBC News.


The scientists think that this species dates back some 65 million years, but multituberculates were around until approximately 40 million years ago, flourishing in the absence of dinosaurs and other large animals. Taeniolabidoidea also underwent a significant increase in body size during this time, with the largest possibly exceeding 100 kilograms (220 pounds), although K. simmonsae was only beaver-size.

"Although mammals and dinosaurs originated about the same time, the dinosaurs took off and became big while mammals stayed small, none bigger than the size of a badger," Brusatte told the National. "What we are seeing with these new fossils is that right after the dinosaurs disappeared, these mammals that survived took advantage and they started growing bigger, and started doing new things, such as changing their diets."

But like the dinosaurs, the multituberculate lineage ultimately met its demise, possibly due to competition from rodents which scurried onto the scene some 57 million years ago


  • tag
  • K-T extinction,

  • fossil,

  • mammal,

  • multituberculate,

  • beaver