THE VERTEBRATE FAUNAS OF THE PLIOCENE RINGOLD FORMATION, SOUTH-CENTRAL WASHINGTON
GUSTAFSON, ERIC PAUL
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GUSTAFSON, ERIC PAUL
The vertebrate fauna of the upper Ringold Formation at the White Bluffs, south-central Washington, has been the subject of several short papers since its discovery in the late 19th century. Additional information from more recent collections, which include remains of many small mammals, expands the knowledge of this White Bluffs local fauna. A rhinoceros mandible from the lowest exposures provides evidence of a second, distinctly earlier fauna, the River Road local fauna. Fossiliferous localities can be correlated by reference to two key beds, the White Bluffs tuff and the Taylor Flat conglomerate, both of which are widely exposed. Vertebrate fossils are most commonly preserved in stream channel conglomerates and less frequently in silt deposits. The White Bluffs local fauna includes three genera of fresh-water snails, two genera of fish (Ictalurus and Archoplites), unidentified anuran amphibians and small reptiles, two or three genera of turtles (Clemmys, Chrysemys?, and possibly Testudo), and 25 genera of mammals. Among the mammalian genera are a mole (Scapanus), two leporids (Hypolagus and Nekrolagus), nine rodents (Paenemarmota or Marmota, Spermophilus?, Ammospermophilus, Thomomys, Castor, Dipoides, Peromyscus, Neotoma, and Ophiomys), an edentate (Megalonyx), six carnivores (Canis, Borophagus, Ursus, Trigonictis, Felis, and a machairodont), a proboscidean (Mammut), an equid (Equus), and four artiodactyls (Platygonus, Megatylopus, Hemiauchenia, and Bretzia). New species are: Hypolagus ringoldensis, a leporid probably derived from H. oregonensis Shotwell; Spermophilus? russelli, a large ground squirrel of uncertain affinities; Ammospermophilus hanfordi, a large antelope ground squirrel; Peromyscus nosher, a deer mouse; Ophiomys mcknighti, a microtine closely related to 0. magilli Hibbard from the Sand Draw local fauna of Nebraska but more primitive than the latter; and Megalonyx rohrmanni, a small ground sloth similar in form to specimens from Hagerman, Idaho. The White Bluffs local fauna is early Blancan (Pliocene) in age. The faunal assemblage is most similar to that of the Hagerman local fauna of Idaho but is probably slightly older. The predominance of browsing forms among the large mammals (particularly Bretzia, Megalonyx, and Platygonus) indicates that the Ringold flood plain supported considerable riparian forest and open woodland, environments extremely restricted in eastern Washington today. Savanna or open grassland, suggested by the presence of Equus and possibly by Megatylopus, may have been important away from the streams, but the absence so far of antilocaprids suggests that these habitats were not important near areas of stream deposition. The River Road local fauna, containing Teleoceras and ?Megatylopus, is probably late Hemphillian in age.