\u201cWe’ve made the picture of the early Eocene more complicated than what we once thought,\u201d said Chris Beard, a Foundation Distinguished Professor at the University of Kansas in Lawrence. \u201cThere will be much more to learn about these fossils, especially from southern Wyoming. There’s a reason we’re working down there.\u201d<\/p>\n
![\"The](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/08\/Smiley-TetoniusJawSize-8.15.26.jpeg\")
The jaw of Tetonius varleyorum, a new species of tarsier-like primate that lived in Wyoming 55 million years ago, on a human fingertip. (Chris Beard)Fascinating And Frustrating<\/p>\n
Wyoming has been a hub of primitive primate paleontology since the 1880s. The first fossils of lemur-like primates, dating to around 55 million years ago, were discovered in the Bighorn Basin around that time.<\/p>\n
\u201cA whole lot of work happened in the late 20th Century in the Bighorn Basin, especially with respect to this animal called Tetonius,\u201d Beard said.<\/p>\n
Tetonius, named after the Tetons, is a \u201cvaguely tarsier-like creature,\u201d as Beard described it. It was around the size of a modern-day mouse lemur, less than a foot long and under 2.5 ounces, but its closest living relatives are modern tarsiers.<\/p>\n
Tarsiers are tiny, tree-dwelling animals known as \u201cdry-nosed\u201d primates. Endangered populations of these tiny primates still exist in the rainforests of Southeast Asia.<\/p>\n
In their study, Beard and his colleagues described a new species of Tetonius, T. varleyorum, from Smiley Draw, an Eocene site in the Great Divide Basin in Sweetwater County.<\/p>\n
\u201cIn Wyoming, you typically find Eocene-aged fossils in mudstone that erodes very easily,\u201d Beard said. \u201cThis particular site is very unusual, if not unique, as it\u2019s a layer of sandstone chock full of fossils. It\u2019s rare to find Eocene fossils in sandstone, so Smiley Draw is exactly the opposite of what we normally expect.\u201d<\/p>\n
According to Beard, the discovery of a new species of Tetonius, based on its age and anatomy, is highly significant.<\/p>\n
\u201cIt\u2019s obviously a different species because it\u2019s younger than the Tetonius and its younger descendant, Pseudotetonius, from the Bighorn Basin,\u201d he said. \u201cThe fossils we found in Sweetwater County occur after that whole lineage has gone extinct in the Bighorn Basin.\u201d<\/p>\n
The study also describes fossils of two rarely found anaptomorphines, another group of prehistoric primates. Arapahovius gazini and Anemorhysis savage have never been found in the Great Divide Basin, and only a handful of other specimens have been found.<\/p>\n
What\u2019s significant is that the fossils of these three primates were found at the same site, which means they coexisted at the same time and place. That just raises further questions about life in the early Eocene.<\/p>\n
\u201cWe\u2019re finding animals that lived together at Smiley Draw that never ever cohabitated in the Bighorn Basin,\u201d Beard said. \u201cTetonius, Arapahovius, and Anemorhysis don\u2019t coexist there, but we find them together here.\u201d<\/p>\n
That\u2019s why Beard said it\u2019s \u201cfrustrating,\u201d from a paleontological perspective, to compare Smiley Draw with the well-researched discoveries in the Bighorn Basin.<\/p>\n
\u201cWe have an idea that animals evolve, they go extinct, and other animals replace them,\u201d he said. \u201cWhat we’re finding at Smiley Draw is the animals that we think are going extinct at a certain time in the Bighorn Basin probably aren’t going extinct elsewhere.\u201d<\/p>\n
![\"The](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/08\/Smiley-IMG_0240-8.15.26.jpg\")
The sandstone of the Wasatch Formation in Sweetwater County. This formation, and much of Wyoming, is rich in Eocene fossils, including three recently discovered prehistoric primates from the Smiley Draw site. (Chris Beard)Gradual And Parallel<\/p>\n
Tetonius, Arapahovius, and Anemorhysis are all omomyids, a family of early tarsier-like primates known from several Eocene sites worldwide.<\/p>\n
Beard said Wyoming\u2019s omomyids are excellent examples of gradual evolution, which is what Charles Darwin proposed in his landmark 1859 book \u201cOn the Origin of Species.\u201d<\/p>\n
\u201cThere was a huge debate in paleontology about how evolution proceeded,\u201d he said. \u201cDid it occur gradually, the way that Charles Darwin predicted, or did it conform more to a punctuated equilibrium model, which was made famous by Stephen Jay Gould and his collaborators?\u201d<\/p>\n
The fossils of Tetonius and Pseudotetonius from the Bighorn Basin are a textbook example of gradual evolution. While they are distinctly different animals, Beard said the fossil record shows \u201cno break in the single lineage chain from primitive to advanced.\u201d<\/p>\n
The key observation is the significant changes in the lower jaws of these primates, which Beard and his colleagues observed in fossils from the Bighorn Basin and the Great Basin Divide.<\/p>\n
\u201cThese animals start out with fairly long lower jaws and lots of teeth in between their back teeth, the molars, and their front teeth, the incisors,\u201d he said. \u201cThrough time, their lower jaws get compacted from front to back. They lose some teeth and develop a rodent-like incisor that sticks out of the front of their jaw, getting bigger and stouter over time.\u201d<\/p>\n
The purpose of this overly large incisor remains a mystery. Beard said that if you asked three different paleontologists, you\u2019d get three different answers.<\/p>\n
\u201cIn my opinion, they’re using that big front incisor to gouge the bark of trees,\u201d he said. \u201cA lot of modern animals do this to stimulate sap or gum or resin to come out of the tree.\u201d<\/p>\n
Tree sap contains a lot of sugar. For a tiny primate with a high metabolism, that sap would be a valuable source of energy and nutrition.<\/p>\n
Is this change in jaw and dental anatomy driven by a change in diet, or were the omomyids perfecting the tools needed for millennia of the same diet? That\u2019s another debated question, but Beard said the latter is the most likely answer. \u00a0<\/p>\n
These questions are significant to the new discoveries from Smiley Draw because they show the same thing happening \u2013 the shortening of the jaw, loss of teeth, and larger incisor \u2013 in Tetonius, but not exactly the same as in the Tetonius from the Bighorn Basin.<\/p>\n
\u201cThe T. varleyorum from Smiley Draw has shorter haws and fewer teeth, so it\u2019s similar but not exactly the same as what we see in the Bighorn Basin,\u201d Beard said. \u201cThese are two different lineages evolving in parallel to achieve the same result.\u201d<\/p>\n
Parallel evolution is a well-documented phenomenon in nature. The legendary finches Darwin collected in the Gal\u00e1pagos Islands are an excellent example, as the different but related birds had beaks shaped to suit their diets on their isolated islands.<\/p>\n
It\u2019s more evidence that something strange was going on in Sweetwater County 55 million years ago.<\/p>\n
![\"The](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/08\/Smiley-IMG_0241-2-8.15.26.jpg\")
The tiny, fossilized jaw in the sandstone of Smiley Draw in southern Wyoming. These fossils are delicate and extremely small, but the implications they have on the paleontological study of the origins and evolution of primates are enormous. (Chris Beard)Hyperthermal Events<\/p>\n
Beard and his colleagues are studying all the mammal fossils recovered from Smiley Draw to see if they have the same story as the recently described omomyids. If they do, it would be further proof that different things were happening in different parts of Wyoming.<\/p>\n
\u201cIt\u2019s an interesting phenomenon,\u201d he said. \u201cWe find animals living side-by-side at Smiley Draw that were already extinct or never lived side-by-side in the Bighorn Basin. They were only going extinct locally in the Bighorn Basin.\u201d<\/p>\n
Climate change might explain this discrepancy. The Eocene was a roller coaster of climate, which usually leads to extinction or adaptation for flora and fauna.<\/p>\n
\u201cWe’ve got lots of iterations of what we call hyperthermal events in the Eocene, where the world warms up very rapidly and cools down again,\u201d Beard said. \u201cWhen the world warmed up, animals that were more tropically adapted spread northward, from Sweetwater County to Park County. When it cooled down, and they were no longer happy, the animals went back down. It’s a very dynamic thing, and we’re picking up a lot of these oscillations by looking at Smiley Draw.<\/p>\n
![\"A](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/08\/Smiley-Tarsius_syrichta-8.15.26.jpg\")
A modern day Philippine Tarsier. Many of the Eocene fossils found in Smiley Draw came from the prehistoric ancestors of these tiny primates. Our Great Uncles<\/p>\n
This new study on prehistoric primates raised more questions than it answered. That\u2019s not a bad thing, as it gives Beard and his colleagues more reasons to return to Smiley Draw.<\/p>\n
Beard said his team was at the site collecting fossils in June. Some of those specimens are already being studied using a micro-CT scanner in North Carolina.<\/p>\n
\u201cI can tell you that we found additional fossils of early primates and primate-like creatures that are totally new just two months ago,\u201d he said. \u201cWe\u2019ll have a lot more to reveal from Smiley Draw.\u201d<\/p>\n