Brooklyn College and CUNY Graduate Center Associate Professor of Anthropology Stephen Chester worked with a team of researchers to uncover fascinating new details about Mixodectes pungens, a long-mysterious mammal that roamed North America in the early Paleocene, just after the extinction of the dinosaurs. For over 140 years, Mixodectes has puzzled paleontologists, with much of what was known limited to fragments of fossilized teeth and jaws. But a groundbreaking new study, led by noted paleontologist Chester, has revealed the most complete skeleton of the species ever found. This discovery sheds light on the mammal’s anatomy, lifestyle, and—perhaps most surprisingly—its proximity to humans and other primates on the evolutionary tree. The study—for which Chester is the lead author—was published on March 11 in the journal Scientific Reports. First described by legendary paleontologist Edward Drinker Cope in 1883, Mixodectes pungens was a small mammal that lived around 62 million years ago. The new research shows that these creatures weighed roughly three pounds as adults, lived in trees, and primarily ate leaves. Even more striking, the study reveals that Mixodectes was a close evolutionary cousin to humans, as well as other modern primates and flying lemurs — an exciting new link to our distant past. Mixodectes pungens(Illustration by Andrey Atuchin) “This fossil skeleton provides new evidence concerning how placental mammals diversified ecologically following the extinction of the dinosaurs,” said Chester, who is also doctoral faculty at the CUNY Graduate Center. “Characteristics such as a larger body mass and an increased reliance on leaves allowed Mixodectes to thrive in the same trees likely shared with other early primate relatives.” Co-author of the study and Yale University anthropologist Eric Sargis, added: “A 62-million-year-old skeleton of this quality and completeness offers novel insights into mixodectids, including a much clearer picture of their evolutionary relationships. Our findings show that they are close relatives of primates and colugos — flying lemurs native to Southeast Asia — making them fairly close relatives of humans.” The newly revealed Mixodectes skeleton is more than just a remarkable fossil — it’s a window into a pivotal moment in mammalian evolution, offering scientists invaluable clues about the origins of some of today’s most fascinating species, including us. And it is just one of many fossils that Chester and his students — including co-author Jordan Crowell, a lecturer at Brooklyn College and Ph.D. candidate at the CUNY Graduate Center — have been studying to understand our evolutionary history. Skeleton of Mixodectes pungens(Photo by Stephen Chester) The skeleton was discovered in New Mexico’s San Juan Basin by co-author Thomas Williamson, curator of paleontology at the New Mexico Museum of Natural History & Science, under a permit from the federal Bureau of Land Management. This rare find includes a partial skull, ribs, vertebral column, and both forelimbs and hind limbs, giving the team crucial insights into how this ancient mammal lived. At a weight of just 2.9 pounds, Mixodectes was relatively large for a tree-dwelling mammal of its time. The structure of its limbs and claws suggests it was adept at clinging to tree trunks and branches, and its molars, evolved to break down plant material, show it primarily ate leaves. Interestingly, Mixodectes was much larger than another small, tree-dwelling mammal — Torrejonia wilsoni — found at the same fossil locality. While Mixodectes had a more leafy diet, Torrejonia primarily ate fruit, hinting at a distinct ecological role for Mixodectes among its contemporaries. In terms of evolutionary placement, two independent cladistic analyses were conducted to determine Mixodectes‘ relationships. The findings confirm that Mixodectes belongs to the group known as primatomorphans — a group that includes living primates and colugos. Other co-authors include Mary Silcox of the University of Toronto Scarborough and Jonathan Bloch of the Florida Museum of Natural History at the University of Florida.
