Part of a series of articles titled Park Paleontology News - Vol. 16, No. 2, Fall 2024.
Article
New Mammal Fossils from Glacier National Park Shed Light on the Rocky Mountains 28 Million Years Ago
Article by Winifred A. Kehl, Jonathan J.-M. Calede, Nicholas A. Famoso, and Kurt N. Constenius
for Park Paleontology Newsletter, Fall 2024
Recent Park Research Yields Rewards
Recent fieldwork in Glacier National Park has uncovered one of the youngest fossils ever found in the Park. Together with two other previously unpublished fossils, this find extends the fossil record of the Park to just about 28 million years before present and opens doorways for future research on this changing landscape. The fossils are published in a recent issue of the scientific journal Geodiversitas (Calede et al., 2024).
A Surprising Discovery
Photo by K. Constenius.
In summer 2022, scientists from the Carnegie Museum of Natural History in Pittsburgh (Pennsylvania) found part of a jaw protruding from the side of a cliff in the Park (Figure 1). It turned out to be most of the lower jaw (left and right sides) of a small deer-like animal. Thanks to the well-preserved teeth, the fossil was identified as Pronodens transmontanus, a species known from elsewhere in Montana. This fossil is the first evidence that P. transmontanus lived in what is now Glacier National Park.
Equally exciting was the age of the fossil—it is one of very few Oligocene-aged fossils (a time period between 33.9 and 22.03 million years old) from the Park. Two other Oligocene-aged fossils had been found in the Park before, but never published. One was the partial jaw of a prehistoric rodent named Paciculus montanus, found several years ago by the late paleontologist Dr. Mary Dawson of the Carnegie Museum of Natural History and sitting in the museum collections there ever since. The other was a jaw from the prehistoric horse Miohippus that a Park ranger found near Kintla Creek in 1997; it was stored in the Park’s collections. When the Pronodens fossil was found poking out of the cliff, scientists and Park employees knew all three fossils should be published to help future research on mammal evolution in the northern Rocky Mountains.
Youngest Fossils in the Park
Photo by K. Constenius.
The newly-published fossils were found in the Kishenehn Formation, an accumulation of prehistoric freshwater sediments that slowly filled in the Kishenehn Basin between about 48 and 23 million years ago (Figure 2; Dawson and Constenius, 2018). A wealth of fossils preserved in the sediments of the Kishenehn Formation have already been discovered from the Park, including plants, insects, spiders, mollusks, fish, and mammals, but they date from the Eocene (56.0-33.9 million years old). The fossils of Pronodens and Paciculus were found in Arikareean-aged rocks dated to about 28.2 million years old (Fan et al., 2021). They are the youngest fossil mammals ever found in the Park! The Miohippus jaw (Figure 3) is slightly older (dated to the Chadronian-Orellan, sometime between 38 and 33 million years old).
Figure 3. Photos of GLAC 26987, a fossil specimen of Miohippus from Glacier National Park: A, lateral view of left dentary; B, medial (inner) view of left dentary; C, occlusal (tooth row) view of left dentary; D, lateral view of right dentary; E, medial view of right dentary; F, occlusal view of the right dentary. Scale bar: 2 cm.
Image from from Calede et al., 2024.
Image modified from Calede et al., 2024.
The new fossils from the Park inform us about some of the animals that lived there long ago. They also enable us to learn more about how different fossil deposits across the northern Rocky Mountains (Montana and Idaho) relate to each other (Figure 4). Do they share some species of mammals or did each of them have a distinct fauna? How similar are the mammals that lived 28 million years ago in Glacier National Park to those of the rest of Montana and Idaho at that time?
The fossil of the rodent Paciculus montanus (Figure 5) found in the Park is the northern-most occurrence of this species ever found. However, it is known from all major fossils sites across Idaho and Montana around 28 million years ago (Black, 1961; Nichols, 1976; Calede, 2020). It appears from this new discovery at a higher latitude that this species was a widespread endemic rodent of the northern Rocky Mountains during the Arikareean. It has definitely earned its name “montanus”!
Image modified from Calede et al., 2024.
In the case of Pronodens transmontanus (Figure 6), a different and interesting story emerges. It is very common in another fossil site of the same age, the Cabbage Patch beds near Missoula, Montana (Calede, 2020), and can also be found in Meagher County (Montana) within the Fort Logan Formation (also around 28 million years old). However, it is absent from a well-studied site (still of the same age) in the Lemhi Valley of Idaho (Nichols, 1976, 1979). Yet, Glacier National Park is farther from the Cabbage Patch beds than the Idaho site. What might this distribution mean?
Figure 6. Photos of GLAC 26988, a fossil specimen of Pronodens transmontanus from Glacier National Park: A, lateral view of right dentary; B, medial view of right dentary; C, lateral view of left dentary; D, medial view of left dentary; E, line drawing of the occlusal view showing tooth morphology of the left dentary. Scale bar: 2 cm.
Image modified from Calede et al., 2024
New Fossils and New Questions
By looking at fossils of the same species and same time period across the region, we can investigate questions like: Were these areas similar to each other environmentally? How did animals move or spread across the landscape? Which areas were corridors for animal movement and which were obstacles? For example, did Pronodens avoid the site in Idaho because the environment there was not suitable, or because it was physically blocked from reaching the area?
We know from the fossils of plants and mollusks (particularly the snails) previously discovered in the Park and in the Cabbage Patch beds that these two areas during the Oligocene had warm temperate climates and were heavily vegetated, with a lot of marshy areas, ponds, lakes, and streams at the time that Pronodens was alive. Maybe such environments were critical for Pronodens and Idaho didn’t have them. Future research will need to follow up on this hypothesis that habitat similarities drove faunal similarities across the northern Rockies during the Arikareean. Pronodens, if it does prove to be limited to certain habitats, may be a useful tool for reconstructing paleoenvironments.
Connected, But Different
Pronodens was present in Glacier just like in areas to the south, but it was not living the exact same life. One clue to its different ecology can be found in its well-preserved teeth, which, as often in paleontology, can be used to tell us about the diet of an animal. Here, the teeth of the Pronodens fossil from Glacier National Park have characteristics that indicate this individual was eating harder foods than the Pronodens from Cabbage Patch. The well-preserved teeth of the Park’s fossil are more robust and broader than those of the many Pronodens fossils of the Cabbage Patch beds; they also show much heavier wear. Additionally, the Park’s Pronodens had bigger jaw muscles, as shown by the larger surface of bone in the back of the jaw compared to the Pronodens from the Cabbage Patch beds. Pronodens adapted to the unique environmental conditions of what is now Glacier National Park.
Not all species show such a pattern however. The comparison of the morphology of the rodent Paciculus montanus from the Park with other specimens of this species from other areas of the Rockies shows no major differences between individuals across sites.
Just One Piece of the Puzzle
Of course, just three new fossil mammals have been identified from Glacier National Park; they hardly build a complete picture of the history of mammal evolution in northern Montana. Many more fossils will need to be recovered and described to better understand the similarities and differences between the Kishenehn Formation and other fossil deposits of the same age across the Rockies.
However, these three fossils, when taken together with other lines of evidence from the Park extracted from studies of the geology, plant fossils, and invertebrates, help build an image of the Park 28 million years ago. When considered with the wealth of information from other fossil deposits of the Rockies, these new fossils also hint at next lines of inquiry for researchers. For example, one hypothesis that should be rigorously tested in the future is that the isolation of intermontane basins 30 to 25 million years ago led to the differences we now see between fossil sites. It will take a lot more field work to find out!
References
- Black, C. C. 1961. Rodents and lagomorphs from the Miocene Fort Logan and Deep River formations of Montana. Postilla 48: 1–20. https://www.biodiversitylibrary.org/page/10580084
- Calede, J. J. M. 2020. Pattern and processes of the mammalian turnover of the Arikareean in the Northern Rocky Mountains. Journal of Vertebrate Paleontology 40(1): 1–17. https://doi.org/10.1080/02724634.2020.1767117
- Calede, J.J., Constenius, K.N., Famoso, N.A., and Kehl, W.A. 2024. Discovery of Oligocene-aged mammals in Glacier National Park (Kishenehn Formation), Montana. Geodiversitas 46(9): 367–389. https://doi.org/10.5252/geodiversitas2024v46a9
- Dawson, M. R., and Constenius, K. N. 2018. Mammalian fauna of the middle Eocene Kishenehn Formation, Middle Fork of the Flathead River, Montana. Annals of Carnegie Museum 85(1):25–60. https://doi.org/10.2992/007.085.0103
- Fan, M., Constenius, K. N., Phillips, R. F., and Dettman, D. L. 2021. Late Paleogene paleotopographic evolution of the northern Cordilleran orogenic front: implications for demise of the orogen. GSA Bulletin 133(11–12): 2549–2566. https://doi.org/10.1130/B35919.1
- Nichols, R. 1976. Early Miocene mammals from the Lemhi Valley of Idaho. Tebiwa 18: 9–47.
- Nichols, R. 1979. Additional early Miocene mammals from the Lemhi Valley of Idaho. Tebiwa 17: 1–12.
Related Links
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Glacier National Park (GLAC), Montana—[GLAC Geodiversity Atlas] [GLAC Park Home] [GLAC npshistory.com]
Last updated: September 27, 2024