Understanding the origins of primates with new fossil evidence

Earliest Palaeocene purgatoriids and the initial radiation of stem primates

Gregory P. Wilson Mantilla, Stephen G. B. Chester, William A. Clemens, Jason R. Moore, Courtney J. Sprain, Brody T. Hovatter, William S. Mitchell, Wade W. Mans, Roland Mundil, and Paul R. Renne

Summarized by Conlan Hale, who is currently a senior at USF planning to graduate in summer 2021 with a B.S. in Geology and B.A. in Mathematics. He plans on becoming a math or science teacher after graduation, and enjoys watching Rays baseball, listening to music, and playing video games when he isn’t finding something new to learn about.

What data were used? Teeth of a new species of purgatoriid mammal (early ancestors of primates) were found in Montana, USA, as well as teeth from other purgatoriid species. The new species signals an earlier date for the spread of the ancestors of primates than originally thought.

Methods: Authors collected tooth and jaw fragments from quarries and the surrounding areas, then analyzed the shapes of the teeth based on 3D model scans.

Results: The researchers discovered several new dental and jaw fragments of Paleocene age (~66 – 56 million years old) leading them to name a new species: Purgatorius mckeeveri (after Frank McKeever, one of the first to sponsor field work in the area where the fossils were found). Based on tooth shape of other specimens from the early Paleocene, researchers were able to classify this new species within the larger family, called the Purgatoriidae. Tooth shape can also be studied to learn about an animal’s diet, and the tooth shape of P. mckeeveri is different from all other purgatoriids in having lower molars with more inflated cusps and rounded crests, as well as having slightly larger molar dimensions than other known species (among other differences). This indicates that this species’ diet was more varied and omnivorous, closer to the early ungulates (ancestors of hoofed mammals) that Purgatorius lived alongside and further from later ancestors of primates, whose diets were primarily fruit, similar to modern lemurs. 

Graph comparing the shapes of molars of Late Cretaceous to Early Paleogene mammals, with P. mckeeveri included. Notice how the Purgatorius species (yellow stars) are closer in diet to the early ungulates (green plus signs) than later plesiadapiforms (other stars).

Why is this study important? This new species pushes back the date of evolution for the ancestors of primates, and they appear from as little as 105 to 139 thousand years after the Cretaceous-Paleogene extinction (~66 million years ago). This means that Purgatorius (and, in turn, other proto-primates) began to thrive across the globe sooner than originally thought. This study also shows how helpful looking at teeth can be as a tool for understanding how and when prehistoric animals lived.

The big picture: These findings show how the ancestors of modern-day primates (and in turn, us humans) adapted and thrived the early Paleogene environment after the loss of the non-avian dinosaurs and many other species. This helps us to further understand both our origins as a species and how speciation as a process works through small changes over time, like the shape of some teeth changing to allow an animal to take advantage of a new food source.

Citation: Wilson Mantilla, Gregory P. et al, 2021, Earliest Palaeocene purgatoriids and the initial radiation of stem primates: Royal Society Open Science 8: 210050. https://doi.org/10.1098/rsos.210050

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.