New Mammal Fossils from Glacier National Park, 28 Million Years Old

Recent fieldwork in Glacier National Park has turned up one of the youngest fossils ever found there. Along with two other fossils never published before, it extends the park's fossil record to about 28 million years ago and opens new lines of research on how this landscape changed. The three fossils were described in 2024 in the scientific journal Geodiversitas.

A jaw in a cliff

In the summer of 2022, scientists from the Carnegie Museum of Natural History in Pittsburgh spotted part of a jaw sticking out of a cliff in the park. It proved to be most of the lower jaw, left and right sides, of a small deer-like animal. Its well-preserved teeth identified it as Pronodens transmontanus, a species known from elsewhere in Montana — and the first evidence that it lived in what is now Glacier.

Just as exciting was its age. It is one of very few fossils from the park dating from the Oligocene, 33.9 to 22.03 million years ago. Two others had been found before but never published:

• part of the jaw of a prehistoric rodent, Paciculus montanus, found years ago by the late paleontologist Mary Dawson of the Carnegie Museum and kept in its collections since;
• a jaw of the early horse Miohippus, found by a park ranger near Kintla Creek in 1997 and stored in the park's collections.

When the Pronodens jaw appeared, scientists and park staff agreed all three should be published to help future research on mammal evolution in the northern Rocky Mountains.

The youngest mammals in the park

All three come from the Kishenehn Formation, freshwater sediments that slowly filled the Kishenehn Basin between about 48 and 23 million years ago. The park's Kishenehn rocks had already yielded a wealth of fossils — plants, insects, spiders, mollusks, fish and mammals — but from the Eocene, 56.0 to 33.9 million years ago. The Pronodens and Paciculus fossils came from Arikareean rocks dated to about 28.2 million years old, making them the youngest fossil mammals ever found in the park. The Miohippus jaw is a little older, from the Chadronian–Orellan, sometime between 38 and 33 million years ago.

How the park fits into the northern Rockies

The fossils also help show how fossil sites across the northern Rockies, in Montana and Idaho, relate to one another — whether they shared species, and how Glacier's mammals 28 million years ago compared with those elsewhere.

• Paciculus montanus is found at all the major fossil sites of that age across Idaho and Montana. The Glacier specimen is the farthest north ever found, suggesting the rodent was widespread across the northern Rockies in the Arikareean — it has earned its name montanus.
• Pronodens transmontanus tells a stranger story. It is very common in the Cabbage Patch beds near Missoula, Montana, and also occurs in the Fort Logan Formation in Meagher County, Montana, both about the same age. Yet it is missing from a well-studied site of the same age in the Lemhi Valley of Idaho — even though Glacier is farther from the Cabbage Patch beds than that Idaho site is.

Comparing the same species at the same time across a region raises questions: were these places environmentally alike? How did animals spread, and what were corridors or barriers? Did Pronodens avoid Idaho because the habitat didn't suit it, or because it could not get there? Plant and mollusk fossils, especially snails, show that Glacier and the Cabbage Patch area were warm-temperate and thickly vegetated when Pronodens lived there, with many marshes, ponds, lakes and streams. Perhaps it needed such places and Idaho lacked them — a hypothesis future research will need to test. If Pronodens was tied to particular habitats, it could help reconstruct ancient environments.

Connected, but different

Pronodens lived in Glacier as it did farther south, but not in quite the same way. Teeth often reveal diet, and the Glacier specimen's teeth are sturdier and broader than those of the many Cabbage Patch specimens, and much more worn — signs it ate harder foods. Its jaw also had a larger area of bone at the back, showing bigger jaw muscles. It had adapted to the conditions of what is now Glacier. Paciculus, by contrast, shows no major differences between specimens from different sites.

One piece of the puzzle

Three fossils cannot give a full picture of mammal evolution in northern Montana; many more will need to be found and described. But together with evidence from the park's geology, plant fossils and invertebrates, they help build an image of Glacier 28 million years ago, and point to new questions — such as whether the isolation of intermontane basins 30 to 25 million years ago produced the differences now seen between fossil sites. Answering that will take much more fieldwork.

Sources

Based on "New Mammal Fossils from Glacier National Park Shed Light on the Rocky Mountains 28 Million Years Ago," by Winifred A. Kehl, Jonathan J.-M. Calede, Nicholas A. Famoso and Kurt N. Constenius, in Park Paleontology News, Fall 2024, published by the National Park Service; it summarises Calede and others (2024) in Geodiversitas.

• The article's photographs, credited to K. Constenius, and its figures from Calede and others (2024) are not reproduced.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.