This tree squirrel species is well-known from the fossil record of the Great Plains, but this 25 million year old partial skull and skeleton from Oregon is the most complete specimen known. The anatomy of the skull and skeleton are nearly identical to living tree squirrels (Sciurus). This supports the idea that tree squirrels are ‘living fossils’, having changed very little for over the last 30 million years.

Photo credit: John Day Fossil Bed National Monument

Ten New Prehistoric Rodent Species Discovered in Oregon’s John Day Basin

Kimberly, Ore. – Paleontologists are pleased to announce the discovery of 10 new prehistoric rodent species found at the National Park Service (NPS) John Day Fossil Beds National Monument and nearby public land administered by the Bureau of Land Management (BLM).

As reported in the current issue of the Annals of Carnegie Museum, Dr. Joshua Samuels (John Day Fossil Beds National Monument) and Dr. William Korth (Carnegie Museum of Natural History, Rochester Institute of Vertebrate Paleontology) examined newly discovered and previously undocumented fossil specimens from the John Day Formation. Their study describes 21 species of rodents in all. The new species include: an early beaver, Microtheriomys brevirhinus, which may be the distant ancestor of living beavers; a dwarf tree squirrel, Miosciurus covensis, smaller than any living in North America today; a primitive pocket mouse, Bursagnathus aterosseus, a possible ancestor of these abundant desert rodents; and a birch mouse, Plesiosminthus fremdi, named for retired John Day Fossil Beds paleontologist Ted Fremd.

“This study fills some substantial gaps in our knowledge of past faunas, specifically smaller mammals. Some of the new species are really interesting in their own right, and will ultimately help improve our understanding of the evolution of beavers and pocket mice,” said Dr. Joshua Samuels. “These finds show that despite this area being studied for well over 100 years, new discoveries continue to be made. Each new discovery helps to give us a fuller picture of Oregon's past.”

This study allows better reconstruction of Oregon’s past ecosystems and improves understanding of how faunas in the region have changed through time. Some of the new rodents are closely related to species from the fossil record of Asia, and help document the dispersal of species across the Bering Land Bridge in the Oligocene. Several of the new species, like the beaver Microtheriomys and pocket mouse Bursagnathus, will help inform studies of how living rodents have evolved.

Oregon’s John Day Basin contains one of the most complete and well-known fossil records on Earth, with nearly 50 million years of time preserved. These fossil beds record the history of ancient ecosystems, changing climate, and plant and animal evolution during the ‘Age of Mammals.’ For 150 years, paleontologists have been visiting the area to collect fossils and study geology. As a result of this research, the John Day Formation boasts an incredibly diverse fauna with over 100 recognized species of mammals, including sabertoothed nimravids, early dogs, three-toed horses, and giant ‘hell pigs.’ These new rodents were collected through decades of collaborative work throughout the John Day Basin by paleontologists from John Day Fossil Beds National Monument, the BLM in Oregon, the University of California - Berkeley, and the University of Washington. While the John Day Fossil Beds National Monument includes many of the important and best studied sites, the majority of fossil localities in the region were found on BLM-managed public lands.

"The National Park Service and BLM have worked together to manage fossil resources in Oregon under an agreement for nearly 30 years," said Shelley Hall, John Day Fossil Beds National Monument Superintendent. "The collaboration between federal agencies has allowed each agency to fulfill their mission of preserving resources for future generations while facilitating important scientific research."

The new study can be found in the current issue of the Annals of Carnegie Museum: www.carnegiemnh.org/science/default.aspx?id=9998

A PDF version of the article can be downloaded from John Day Fossil Beds National Monument at: www.nps.gov/joda/learn/news

Additional information about John Day Fossil Beds National Monument is available online at: www.nps.gov/joda