The Oligocene Fossils Behind the 2025 National Fossil Day Artwork

Eastern and central Oregon's John Day River Basin is badlands, sagebrush steppe and riverside habitat today. Its rocks hold the living world that came before, and they tell a continuous story of how life and its surroundings changed in the northwestern United States across the Cenozoic Era, from the Eocene Epoch to the late Miocene. Paleontologists from many institutions have worked these rocks for more than 160 years.

John Day Fossil Beds National Monument, run by the National Park Service, was established on October 8, 1975. It covers 13,944 acres in three units — Sheep Rock, Painted Hills and Clarno — which hold only part of the wider fossil beds, so the park works with other federal, state and tribal partners and with private landowners. About 210,000 visitors a year come for recreation and for the 45 million years of fossil history in the region, and park paleontologists and their colleagues are still making discoveries.

The 2025 National Fossil Day artwork takes its subject from here: the 29-million-year-old Oligocene community of the John Day Formation's Turtle Cove Member.

The colorful badlands of John Day Fossil Beds National Monument. NPS photo.

Layers of rock, layers of time

The monument's rocks begin in the Cretaceous. The oldest, the Late Cretaceous Gable Creek Formation, formed where a large river met a shallow coast; within the monument it has yielded few fossils, mostly bits of wood. Nearly everything known from fossils here comes from the Cenozoic rocks above it.

The Oligocene: a world drying out

The Oligocene ran from approximately 34 to 23 million years ago. Over it, the warm, wet Eocene world — forested almost everywhere, Antarctica included — gave way to the cooler, drier climate that later favored the open woodlands and grasslands of the Miocene. The Turtle Cove Member captures the start of that shift in the Pacific Northwest, from forest toward open woodland and, eventually, sagebrush steppe, and the animals in the artwork carry clues to it.

One of America's last primates

Lemur-like primates called adapiformes lived across North America in the Paleocene, Eocene and Oligocene. Most had died out by the end of the Eocene, though a few species hung on into the early Miocene. One of them, Ekgmowechashala zancanellai, is known only from the Turtle Cove Member; other Ekgmowechashala fossils come from South Dakota, Nebraska and Texas. The name means "little cat man" in Sioux. It was small, with teeth suited to soft fruit and insects.

The artwork places it in a fruiting hackberry tree beside a grasshopper. Both are in the monument's fossil record: hackberry leaves and seeds, and the first fossil grasshopper egg clutch ever found. A primate living here is evidence that forest still dominated the region in Turtle Cove times.

Left: lower teeth of Ekgmowechashala zancanellai. Right: a restoration of the animal. NPS/art by Benji Paysnoe.

Horses and a two-horned rhino

Hoofed mammals appear in the monument's Eocene, Oligocene and Miocene rocks alike. They fall into two groups: artiodactyls, with an even number of toes, and perissodactyls, with an odd number. The Turtle Cove Member has artiodactyls — peccaries, camels, early deer-like animals, oreodonts (with features of both pigs and camels) and a giant omnivore, an entelodont — and perissodactyls, the three-toed horses and rhinos.

The art shows two perissodactyls. Miohippus annectens was a small three-toed horse weighing 25 to 30 kg as an adult, whose descendants split into lines suited to forest or to open grassland. Thomas Condon, the founding figure of John Day paleontology, sent Miohippus fossils to Othniel Charles Marsh, who wrote to Charles Darwin that they supported his theory of evolution. Diceratherium annectens was an early rhino with two horns side by side at the tip of its nose.

Left: a Miohippus skull. Right: two Miohippus from the Turtle Cove Member. NPS images.

Left: skull and hind-limb bones of Diceratherium from the Turtle Cove Member. Right: its mounted skeleton. NPS photos.

A false cat and a big-eared little dog

Carnivorans are also common in the monument's rocks: early relatives of dogs, weasels, raccoons, bears and cats, and extinct groups such as false cats and bear-dogs. The artwork has two from the Turtle Cove Member.

Nimravus brachyops was a nimravid, or false sabertoothed cat — part of the group that also holds true cats, hyenas, civets and mongooses. Nimravids had short, cat-like skulls, and many had saber teeth, but unlike true cats they lacked complete bony walls around the ear canals (the auditory bullae) and probably had cartilage there instead, like civets. Nimravus was leopard-like, with short sabers, and could hunt in forest and open country alike, taking prey such as Miohippus.

Cynarctoides lemur was a small, raccoon-like dog that probably hunted or ate fruit and nuts. It belonged to the borophagines, the "bone-crushing" dogs, whose heavy cheek teeth eventually let some species crack bones as hyenas do. Enlarged structures around its ears suggest big ears like a fennec or bat-eared fox's, and like them it likely hunted by sound for insects, small reptiles and rodents.

Left: skull and forelimb bones of Nimravus from the Turtle Cove Member. Center: a Nimravus specimen from the John Day Basin as published by Edward Drinker Cope in 1880. Right: a reconstruction of Nimravus. NPS images.

Sources

Rewritten from the National Park Service article "Fossils of the 2025 National Fossil Day Artwork" (public domain). The source dates the adapiform primates to "66–25 million years ago" while giving the Oligocene as ending 23 million years ago; neither span is repeated here. The National Fossil Day painting and the commissioned poster are not reproduced, nor is an American Museum of Natural History drawing of Cynarctoides.