This Curious Mammal Lived On Earth 62 Million Years Ago And Was A Close Relative Of Humans
During the early Paleocene, about 66 to 56 million years ago, a species of small mammal known as Mixodectes pungens inhabited western North America. It was first discovered more than 140 years ago by paleontologist Edward Drinker Cope.
The little information we know about them has come from fossilized teeth and tiny jawbone fragments collected in the years since.
But now, a new study of the most complete and well-preserved skeleton of the species has provided some answers about its diet, anatomy, and behavior.
This particular Mixodectes pungens specimen is 62 million years old and represents a mature adult. It weighed about three pounds, lived in the trees, and dined on leaves. It also shows that these creatures are among humans’ closer evolutionary relatives.
“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,” said Eric Sargis, a professor of anthropology at Yale University.
“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.”
Mixodectes belonged to mixodectids, an extinct family that lived during the Paleocene. The skeleton in this study was collected in New Mexico’s San Juan Basin. It includes forelimbs, hind limbs, a partial skull with teeth, spinal column, and rib cage.
Based on the anatomy of the animal’s limbs and claws, it was a tree-dweller and could vertically cling to branches and tree trunks. Its molar teeth could break down tough material, indicating that it was omnivorous and ate leaves most of the time.
“This fossil skeleton provides new evidence concerning how placental mammals diversified ecologically following the extinction of the dinosaurs,” said Stephen Chester, a co-author of the study and a paleontologist at the Yale Peabody Museum.
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“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.”
For a tree-dwelling mammal in North America during the early Paleocene, Mixodectes was pretty large. The skeleton is much larger than a partial skeleton of Torrejonia wilsoni, a small arboreal mammal from an extinct group of primates called plesiadapiforms.
Mixodectes mostly ate leaves, but Torrejonia subsisted primarily on fruit. The differences in their size and diet suggest that mixodectids were unique from their tree-dwelling counterparts in the early Paleocene.
It was also confirmed that mixodectids were euarchontans, a group of mammals consisting of primates, treeshrews, and colugos.
One analysis implied that they were archaic primates, while the other proved that mixodectids are primatomorphans, a group that includes primates and colugos but not treeshrews.
Overall, the study has not ended the debate over mixodectids’ place on the evolutionary tree, but it has helped to narrow it down. The findings were published in Scientific Reports.
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