Meet Cimolodon desosai: The tiny mammal that survived when dinosaurs didn’t

Seventy-five million years ago, a Cimolodon desosai lived in the waning days of the Cretaceous period. While dinosaurs ruled the earth, this small mammal was omnivorous, and its biological makeup gave it exactly what it needed in order to survive an upcoming extinction event, which happened 66 million years ago, as noted by the University of Washington.

Fossils found recently include relatively complete skeletal remains, including most of the skull and other parts of the skeleton, which have provided an exceptional look into how these multituberculate mammals managed to survive when dinosaurs went extinct. By studying these fossils, palaeontologists can see how mammals back then had developed evolutionary resiliency and subsequently provided a pathway to how modern mammals exist today. Such a discovery offers invaluable insights into the adaptive traits that allowed early mammals to thrive during Earth’s most transformative historical transition.

The tiny mammal that outlived the dinosaurs

Cimolodon desosai was able to survive due to its small size and dietary flexibility. The research published in the Journal of Vertebrate Palaeontology shows that this species of mammal is about the same size as a modern hamster, which allowed Cimolodon desosai to take advantage of ecological niches that larger dinosaurs could not access. In addition, because Cimolodon desosai was omnivorous, it was also able to act as a buffer against the ecological instability that triggered the collapse of food chains during a mass extinction.

A breakthrough in skeletal discovery

The discovery of Cimolodon desosai was significant, since previous discoveries from the area were tooth fragments. The recovery of this specimen includes many more skeletal elements than previously found, such as the skull, jaws, femur, and ulna. The research team led by the University of Washington used micro-CT scanning to produce high-resolution images of Cimolodon desosai, which provided definitive evidence that this species differs from all other Cimolodon species. The recovery of the post-cranial elements also allows for a greater understanding of the locomotion and habitat use of these ancient mammals.

The evolutionary legacy of the multituberculates

The multituberculata, a very successful group of mammals that first appeared in the Jurassic Period and lived for more than one hundred million years, includes Cimolodon desosai. According to senior author Gregory Wilson Mantilla, fossils of Cimolodon have been found throughout western North America, from the western portion of Canada all the way to Mexico. As noted in a study by the University of Washington, the name of the species was chosen to honour Michael de Sosa VI, the field assistant who first discovered the fossil in 2009. One of the most important parts of this discovery is how it relates to our understanding of the evolution of early mammals before and after the mass extinction.