For over 140 years, Mixodectes pungens, a small mammal from the early Paleocene of western North America, was shrouded in mystery. Known mostly from fossilized teeth and jawbone fragments, the creature left scientists guessing about its habits and its place in the evolutionary tree. That is, until now.
A groundbreaking Yale study has analyzed the most complete skeleton of Mixodectes ever discovered. The findings illuminate its anatomy, behavior, and surprising evolutionary ties.
According to the study, led by Yale anthropologist Eric Sargis and Brooklyn College’s Stephen Chester, this mammal weighed around 3 pounds, lived in trees, and primarily ate leaves. Moreover, researchers revealed that Mixodectes shares close evolutionary connections with primates and colugos (flying lemurs), putting it relatively near humans on the evolutionary tree.
“This 62-million-year-old fossil gives us an unprecedented look into mixodectids, showing their relationships to early primates,” said Sargis.
Co-author Thomas Williamson unearthed the skeleton in New Mexico’s San Juan Basin. The fossil, which includes parts like the skull, teeth, spine, ribs, and limbs, provides detailed insights into the creature’s anatomy.
The Mixodectes skeleton shows it was adapted for life in trees, able to cling vertically to trunks and branches. Its molars, designed to handle tough vegetation, suggest it was omnivorous, with leaves being a major part of its diet.
Remarkably, its larger size—nearly 3 pounds—set it apart from smaller contemporary tree-dwellers, such as Torrejonia Wilson, an extinct primate relative whose diet consisted mainly of fruit.
Mixodectes occupied a unique ecological niche in the Paleocene, the epoch following the mass extinction of the dinosaurs. Its larger body size and leaf-heavy diet allowed it to thrive alongside early primate relatives in the same treetops.
Scientists identified the genes that shape our skeletons
Two evolutionary analyses confirmed that Mixodectes belongs to the Euarchonta group of mammals, which includes treeshrews, primates, and colugos. Although there’s debate over whether mixodectids were early primates, both analyses confirmed their ties to primates and colugos within the group Primatomorpha.
“This study narrows the evolutionary debate surrounding mixodectids and gives us a clearer picture of their relationships,” said Sargis.
Mixodectes pungens, once a paleontological puzzle, now offers a vibrant life story after the dinosaurs and how ancient mammals diversified to fill newly vacated ecological niches.
Scientists continue to piece together the evolutionary paths connecting these small mammals to their modern relatives, including humans. This discovery deepens our understanding of early mammalian life and highlights the incredible resilience and adaptability of life on Earth.
Journal Reference
- Chester, S.G.B., Williamson, T.E., Crowell, J.W. et al. New remarkably complete skeleton of Mixodectes reveals arboreality in a large Paleocene primatomorphan mammal following the Cretaceous-Paleogene mass extinction. Scientific Reports 15, 8041 (2025). DOI: 10.1038/s41598-025-90203-z
