Ancient Mammal Mystery Solved: Fossil Sheds Light on Tree-Dw...

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For over 140 years, the small mammal Mixodectes pungens remained an enigma. First described in 1883 by renowned paleontologist Edward Drinker Cope, it was known only through scattered fossilized teeth and jaw fragments. Now, a new study based on the most complete Mixodectes skeleton ever discovered has brought this long-lost species vividly back to life.

The fossil, unearthed in New Mexico’s San Juan Basin, has allowed researchers to reconstruct key details about the animal’s size, lifestyle, diet, and evolutionary history. The study, published in Scientific Reports, was co-authored by Yale anthropologist Eric Sargis and led by Stephen Chester of Brooklyn College, CUNY.

The specimen includes parts of the skull, teeth, spine, ribcage, and limbs. Based on this, the team determined that Mixodectes was a mature adult weighing about 2.9 pounds (1.3 kilograms). Its skeletal structure, particularly in the limbs and claws, shows that it lived in trees and was well-adapted for climbing and clinging to branches. Its teeth suggest a mostly leaf-based diet, indicating it was an omnivore with a preference for tough, fibrous plant material.

“This 62-million-year-old fossil gives us a much clearer understanding of Mixodectes and its place in the mammalian family tree,” said Sargis, who is also a curator at the Yale Peabody Museum. “It confirms that mixodectids were close relatives of primates and colugos—flying lemurs native to Southeast Asia—placing them relatively near humans on the evolutionary tree.”

The study provides a rare glimpse into the ecological dynamics of the early Paleocene, the period following the mass extinction that ended the age of dinosaurs. Mixodectes, with its relatively large body size for an arboreal mammal, thrived in forest environments alongside smaller species like Torrejonia wilsoni, a fruit-eating plesiadapiform thought to be an early primate relative. The contrasting diets and sizes of the two species suggest that Mixodectes occupied a distinct ecological niche, helping to shape the early diversification of mammals after the dinosaurs’ extinction.

Phylogenetic analyses placed Mixodectes within Euarchonta, a group that includes primates, colugos, and treeshrews. While one analysis positioned mixodectids as archaic primates, another classified them within the broader group of primatomorphans, which includes primates and colugos but excludes treeshrews.

“This doesn’t entirely settle the debate over their exact evolutionary placement,” Sargis explained, “but it significantly narrows the possibilities and confirms that mixodectids were much closer to primates than we previously understood.”

The fossil was collected under a Bureau of Land Management permit by co-author Thomas Williamson of the New Mexico Museum of Natural History & Science. Additional co-authors include Jordan Crowell of CUNY, Mary Silcox of the University of Toronto Scarborough, and Jonathan Bloch of the Florida Museum of Natural History.

Together, their findings not only solve a century-old paleontological puzzle but also deepen our understanding of how mammals rapidly evolved and adapted in the shadow of the dinosaurs’ extinction—laying the groundwork for the rise of primates, and eventually, humans.

Posted : 31/03/2025 4:33 pm

Ancient Mammal Mystery Solved: Fossil Sheds Light on Tree-Dwelling Relative of Humans

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Ancient Mammal Mystery Solved: Fossil Sheds Light on Tree-Dwelling Relative of Humans

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