Paleontologists Dr William Korth of Rochester Institute of Vertebrate Paleontology and Dr Joshua Samuels of John Day Fossil Beds National Monument have described four new genera and ten new species of prehistoric rodents that lived in what is now Oregon during the Oligocene epoch, between 30 and 22 million years ago.
The beaver Microtheriomys brevirhinus lived in what is now John Day Basin, Oregon, about 29 million years ago. The image is an artist’s rendering of the extinct giant beaver Castoroides sp., by Charles R. Knight, 1904.
The newly-discovered genera include: the early beaver Microtheriomys brevirhinus; the dwarf tree squirrel Miosciurus covensis; the primitive pocket mouse Bursagnathus aterosseus; the birch mouse Plesiosminthus fremdi; an early relative of beavers, Allotypomys pictus; Proapeomys condoni; Apeomys whistleri; Neoadjidaumo arctozophus; Proheteromys latidens; and Trogomys oregonensis.
Of these ten new species, four represent completely new genera: Allotypomys, Microtheriomys, Proapeomys, and Bursagnathus.
“This study fills some substantial gaps in our knowledge of past faunas, specifically smaller mammals,” said Dr Samuels, who is a co-author of the paper published in the Annals of Carnegie Museum.
“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.”
These new rodents were collected through decades of collaborative work throughout the John Day Formation, Oregon.
Specimens of Microtheriomys brevirhinus. Image credit: William Korth / Joshua Samuels.
According to the paleontologists, Microtheriomys brevirhinus may be the distant ancestor of living beavers.
Apeomys whistleri, Neoadjidaumo arctozophus, and Proapeomys condoni are early relatives of modern-day pocket gophers and kangaroo rats.
The pocket mouse Bursagnathus aterosseus is a possible ancestor of these abundant desert rodents.
“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,” the scientists said.
“Several of the new species, like the beaver Microtheriomys brevirhinus and pocket mouse Bursagnathus aterosseus, will help inform studies of how living rodents have evolved.”
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William W. Korth & Joshua X. Samuels. 2015. New rodent material from the John Day Formation (Arikareean, Middle Oligocene to Early Miocene) of Oregon. Annals of Carnegie Museum, vol. 83, no. 1, pp. 19-84
