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A field crew collects fossils along the Smiley Draw sandstone in Wyoming.
Photo Credit: Robert Anemone
Scientific Frontline: Extended "At a Glance" Summary: Tetonius varleyorum and Early Primate Evolution
The Core Concept: Tetonius varleyorum is a newly identified, mouse-lemur-sized species of extinct omomyid primate that challenges the previously accepted step-by-step evolutionary model of early mammals.
Key Distinction/Mechanism: Past models, based heavily on localized fossils from the Bighorn Basin, suggested a single, unbranching evolutionary line (anagenesis) for the genus Tetonius; however, fossils from the new Wyoming locale prove a more complex pattern of branching speciation.
Origin/History: Dating back roughly 55 million years to the warm Eocene epoch, the fossils were collected at the Smiley Draw site in Wyoming. The findings were published in the Journal of Human Evolution by researchers from the University of Kansas and the University of North Carolina at Greensboro.
Major Frameworks/Components:
- Omomyidae Family Tree: Extinct, early "true primates" that represent a crucial branching point near the common ancestors of modern lemurs, monkeys, apes, and humans.
- Biogeographical Sampling: The crucial role of expanding fossil recovery beyond well-documented basins to prevent skewed interpretations of evolutionary history.
- Anagenesis vs. Cladogenesis: The shift from viewing evolutionary transitions as a straight, non-branching progression to recognizing complex, branching speciation events in the fossil record.
Branch of Science: Paleontology, Evolutionary Biology, and Biological Anthropology.
Future Application: This research mandates a reevaluation of established mammalian phylogenetic trees, and it will drive expanded geological surveys outside traditional, heavily sampled fossil basins.
Why It Matters: By overturning a textbook example of straight-line evolution, this discovery highlights the intricate, branching reality of how our earliest primate ancestors diversified across the Northern Hemisphere.
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| Image of the holotype jaw of Tetonius varleyorum. Photo Credit: Courtesy of Parker Rhinehart. |
A new study from the University of Kansas complicates the picture of primates living in North America some 55 million years ago during the Eocene, a warm period that allowed mammals to diversify quickly.
The research, published in the Journal of Human Evolution, introduces a new species of ancient primate and challenges long-held assumptions about the sequence of evolutionary traits in a key fossil primate genus of the epoch.
“The paper is about a new species of an omomyid primate, a primate family close to the top of the family tree of modern primates—with lemurs on one side and apes, humans, and monkeys on the other,” said lead author Parker Rhinehart, a doctoral student with the KU Biodiversity Institute and Natural History Museum. “The branch point where they meet up at the top is where the omomyids fall. They're true primates, but they're extinct. They appear about 55 or 56 million years ago across the Northern Hemisphere.”
The new paper describes a new species of the genus Tetonius, an omomyid species comparable in size to a modern mouse lemur. The findings suggest its evolution might be more complex than a step-by-step progression earlier suggested by fossils from a single basin.
“We named it Tetonius varleyorum,” Rhinehart said. “Varley is the name of a family that runs a truck stop near the campground where we stay when we're collecting fossils, and they’ve been a great help to us.”
The KU researcher said identifying ancient primate fossils in the field typically requires hunting tiny fossil jaws and teeth—the only body parts tough enough to withstand erosion over geologic time. He added that the KU paper analyzes fossils from Smiley Draw, a different Wyoming locale outside of the better-sampled Bighorn Basin.
Co-author Robert Anemone, a professor of anthropology at the University of North Carolina at Greensboro, discovered the Smiley Draw site and has conducted fieldwork there for several years. Co-author K. Christopher Beard, senior curator at the KU Biodiversity Institute and Foundation Distinguished Professor in KU's Department of Ecology and Evolutionary Biology, is advising Rhinehart’s doctoral research.
“This is really important to the Tetonius story,” Rhinehart said. “Because so many scientific ideas only really consider the fossils from the Bighorn Basin, they just don't take in the whole picture. One of the things our paper points out is when you start incorporating fossils from outside of the Bighorn Basin, this picture becomes a little bit more complicated.”
Rhinehart said the paper’s description of Tetonius varleyorum as a new fossil species gives fresh detail to the biogeographic and evolutionary history of primates.
For instance, the KU researcher cited a landmark 1987 paper by paleontologists Thomas Bown and Kenneth Rose, which includes a famous figure depicting the evolution of fossil Tetonius jaws found in the Bighorn Basin.
“One of the premier papers from that basin has this figure depicting a proposed evolutionary transition from an early form of Tetonius,” he said. “It’s upheld as a great example of an evolutionary transition—reflecting a true transition in the fossil record.”
While the earlier paper and figure have been vital to the Tetonius story, Rhinehart said fossils from Smiley Draw described in the new research would challenge some of its conclusions.
“The 1987 paper claims that there is no branching of the tree, going from one intermediate species of Tetonius to the next with no branching speciation events,” he said. “Evolutionary biologists call this ‘anagenesis.’”
Published in journal: Journal of Human Evolution
Authors: Parker D. Rhinehart, Robert L. Anemone, and K. Christopher Beard
Source/Credit: University of Kansas | Brendan M. Lynch
Edited by: Scientific Frontline
Reference Number: pal081026_01