New Rodent Material from the John Day Formation (Arikareean, Middle Oligocene to Early Miocene) of Oregon

Abstract

The John Day Formation of Oregon is one of the richest and best studied assemblages in North America. Including seven members and spanning about 20 million years, there are over 150 vertebrate species known from the John Day Formation. The rodent faunas of John Day have not been as well studied as larger mammals, with many families having received little attention in the last hundred years. Here, twenty one species of rodents are described, based on new discoveries and previously unpublished specimens from the John Day Formation. The new material includes four new genera and species; the eutypomyid Allotypomys pictus, the anchitheriomyine castorid Microtheriomys brevirhinus, the eomyid Proapeomys condoni, the heteromyid Bursagnathus aterosseus; and six new species: the sciurine sciurid Miosciurus covensis, the eomyids Apeomys whistleri and Neoadjidaumo arctozophus, the heteromyids Proheteromys latidens and Trogomys oregonensis, and the sicistine dipodid Plesiosminthus fremdi. The problematical eomyid species, "Florentiamys" lulli Wood, 1936a, is referred questionably as a new combination, ?Proapeomys lulli (Wood, 1936a). Emended diagnoses of Miosciurus ballovianus (Cope, 1881) and Proheteromys thorpei Wood, 1935b, are offered based upon substantially more complete material than was previously known for either. Biostratigraphic ranges of the newly described rodents allow more direct comparison with other contemporaneous faunas from North America. These new rodents also allow better reconstruction of past ecosystems and are vital for understanding how faunas have changed through time in the region.

Oldest skeleton of a fossil flying squirrel casts new light on the phylogeny of the group

“…In North America, aside from Sciurion the larger-sized genus Petauristodon is also present from the late Oligocene to the late Miocene (Goodwin, 2008) (Figure 8). While  Sciurion  is already known since the early Oligocene (33.5-33.0 Ma) (Bell, 2004), the oldest record of  Petauristodon is a single molar dated between 25.9 and 23.8 Ma from the John Day Formation of Oregon (Korth and Samuels, 2015). Subsequent records date back to the early Miocene (ca.…”

Morphology of an Early Oligocene beaverPropalaeocastor irtyshensisand the status of the genusPropalaeocastor

“…It is generally believed that Agnotocastor and Propalaeocastor are close to each other (Korth, 2001; Korth, 2004; Korth & Samuels, 2015; Mörs, Tomida & Kalthoff, 2016). Our phylogenetic analysis suggests that some species of “ Agnotocastor ”, namely of P .…”

The first Eocene rodents from the Pacific Northwest, USA

“…The diminutive size of these incisors and their shape suggest that they could all belong to one species, likely an eomyid, dipodoid, or possibly Microparamys. Though no Eocene eomyids have been documented from the Northwest, there are five Oligocene (Arikareean) eomyid species known from the John Day Formation (Korth and Samuels, 2015) and a number of eomyids known from the middle Eocene of California (Flynn, 2008). Metanoiamys agorus is known from the early Uintan (Ui1) age Friars Formation, and the middle Uintan (Ui2) age Murray Canyon and Mesa Drive Local Faunas (Chiment and Korth, 1996;Flynn, 2008); while M. fantasma is known from the Uintan or Duchesnean age Hartman Ranch Local Fauna (Lindsay, 1968).…”

“…While the incisors or the Bridgerian dipodoid Elymys have rather thin enamel (Emry, 2007), a lower incisor of the Chadronian N. simplicidens described by Emry and Dawson (1972) had thick enamel like that of the Clarno incisors, but it is substantially smaller. A single dipodid is known from the Oligocene of Oregon, Plesiosminthus fremdi from the late Arikareean (Ar3) age Kimberly Member of the John Day Formation (Korth and Samuels, 2015).…”