Mammals once shared the planet with dinosaurs until a catastrophic event 66 million years ago wiped out about 75% of life on Earth. Nevertheless, some species managed to survive. Among them were small, rodent-like mammals that belonged to the genus simolodon. These animals were part of the multituberculates, a long-lived group that first appeared during the Jurassic period and persisted for more than 100 million years before eventually becoming extinct. By studying them, scientists can better understand how early mammals faced mass extinction and later evolved into the diverse forms we see today.
A team led by researchers at the University of Washington has identified a new species within this genus based on a fossil found at a site in Baja California. It is estimated that this fossil is about 75 million years old. newly named species, Simolodon desosaiIt was about the size of a golden hamster. According to researchers, it probably roamed both on the ground and in trees and its diet was fruits and insects.
The findings were published on April 22 Vertebrate Paleontology Journal.
“genus simolodon The dinosaur was a very common mammal during the Late Cretaceous, the last era of the dinosaur era. simolodon “The fossils have been found throughout western North America, from western Canada to Mexico,” said senior author Gregory Wilson Mantilla, UW professor of biology and curator of vertebrate paleontology at the Burke Museum. Simolodon desosaiWas the ancestor of the species that survived the extinction event. It and its descendants were relatively small and omnivorous – two traits that were advantageous for survival.”
Fossil discovery reveals rare skeletal details
The fossil was first discovered in 2009 by Wilson Mantilla and his team. Unlike many similar discoveries, which often contain only teeth, this specimen includes a wide range of remains. The team recovered teeth, a skull, jaws, and parts of the skeleton, including a femur and an ulna.
“It is very difficult to find fossils at this site compared to other areas,” Wilson Mantilla said. “At first, my field assistant just found a small tooth sticking out. If he had still found it, I would have been over the moon. But then when we looked inside the crack in the rock, we could see there were even more bones.”
More than just the teeth allowed researchers to estimate the animal’s size, body composition, and potential activity. These details help scientists better reconstruct the environment in which they lived and expand knowledge of multituberculates as a whole.
Advanced imaging helps identify new species
To analyze the fossil, the team used digital imaging along with micro-computed tomography, or micro-CT, which produces highly detailed images. Then they compared the teeth C. Desosai with related species simolodon To confirm this the genus was distinct.
“In ancient times, things were named after characteristics of their teeth,” Wilson Mantilla said. “If you find a skeleton that’s missing teeth, sometimes it’s hard to associate it with a name.”
Honoring the discoverer of the fossil
The species was named in honor of Michael de Sousa VI, the field assistant who first observed the fossil. De Sousa died while the research team was still studying the specimen.
Wilson Mantilla said, “He was a great field assistant and he was like a little brother to me.” “It’s a great model to be associated with.”
Additional co-authors are Isiah Nubbins, a UW doctoral student in biology, David Fastowski at the University of Rhode Island; Yu Zhang, who completed this research as a UW postdoctoral fellow in biology; Meng Chen, who completed this research as a UW doctoral student in biology; and Marisol Montellano-Ballesteros and Dalia García Alcantara at the Universidad Nacional Autonoma de México.
This research was funded by UC MEXUS-CONACYT, Dirección General de Asuntos del Personal Académico PAPIIT IN111209-2, UW College of Arts and Sciences, UW Department of Biology, and the American Philosophical Society.