Evolution in Yoderimyinae (Eomyidae: Rodentia), with new material from the White River Formation (Chadronian) at Flagstaff Rim, Wyoming

Three species of Yoderimyinae (Eomyidae: Rodentia) are recognized from the lower part of the White River Formation (early to medial Chadronian) in the Flagstaff Rim area, Wyoming. The new material allows an improved diagnosis for the subfamily. The enamel microstructure of Yoderimyinae supports its inclusion in the Eomyidae. A new genus, Zemiodontomys, is established for Yoderimys burkei Black, and new material, including upper dentition, is referred to this species. This genus differs from Yoderimys in having higher crowned and more lophodont teeth and in lacking P3. A second new genus, Litoyoderimys, is established for Yoderimys lustrorum Wood, and a new species, L. auogoleus, is referred to the genus. This genus has lower crowned, more cuspate teeth than Yoderimys. Through early and medial Chadronian time, evolution in yoderimyines includes the following morphologic transformations: increase in size; increase in crown height and lophodonty of cheek teeth; reduction of P3 (from double-rooted, to single-rooted, to absent); increase in relative size of P4 and p4; and increased longitudinal torsion of the mandibl

New material of the Oligocene muroid rodent Nonomys, and its bearing on muroid origins. American Museum novitates ; no. 2712

14 p. : ill. ; 26 cm.Includes bibliographical references (p. 14)."New material shows that Nonomys simplicidens has the dental formula, and some of the dental characters, of the Cricetidae. These are combined with an hystricomorphous zygomasseteric structure like that in Dipodoidea, i.e., the enlarged foramen for the medial masseter is separated by a lamina of bone from a smaller foramen which transmits the infraorbital nerve and blood vessels, and there is virtually no development of a zygomatic plate. This ambiguous combination of characters is seen also in late Eocene Simimys, which has been classified as a dipodoid and as a muroid. Nonomys and Simimys are interpreted as members of an early radiation of myodont rodents, with derived characters that place them in the Muroidea rather than Dipodoidea, but with a combination of characters that excludes them from any presently defined family"--P. [1]

Cricetid

14 p. : ill. ; 24 cm.Includes bibliographical references (p. 13-14)."Two specimens, a partial right mandibular ramus with M[subscript 1]-M[subscript 3] and an isolated left M[subscript 2], represent a new genus and species of rodent, Nanomys simplicidens. The teeth of this rodent are so lacking in special characters that its phylogenetic position is difficult to interpret, but it seems best referred to the Cricetidae"--P. [1]

Relationships of Apternodus

117 p. : ill., map ; 26 cm.Includes bibliographical references (p. 110-117).We describe and illustrate new, middle Cenozoic fossils of dentally zalambdodont, North American placentals, including six relatively complete crania of Apternodus and two of Oligoryctes, as well as many partial skulls, mandibles, and teeth of these and other taxa. Several of the new Apternodus specimens are also associated with postcrania. We recognize seven species of Apternodus, three of which are new, formally propose the combination Oligoryctes altitalonidus, and recognize two other genera of small, North American, anatomically zalambdodont placentals, Parapternodus and Koniaryctes. We regard two other taxa previously associated with North American fossil zalambdodonts, one Bridgerian and the other Tiffanian, as valid but do not name them in this paper. In addition, we argue that dental zalambdodonty entails a primary occlusal relationship between the paracone and the ectoflexid, and the reduction or absence of the metacone and talonid basin. A phylogenetic analysis of cranial, dental, and postcranial characters of 30 fossil and Recent taxa leads us to conclude that (1) the Apternodontidae as defined in previous literature is not monophyletic and should be restricted to seven species of Apternodus, (2) the genus Oligoryctes contains at least two species and has a considerably longer geologic record than Apternodus, (3) neither Micropternodus nor currently known Paleocene taxa are closely related to Apternodus or Oligoryctes, and (4) a case can be made for a close relationship among modern soricids, Parapternodus, Koniaryctes, Oligoryctes and Apternodus to the exclusion of other insectivoran-grade taxa. With the use of ordered, multistate character transformations, Solenodon comprises the sister taxon to a soricid-fossil zalambdodont clade

A new species of Agnotocastor (Rodentia, Castoridae) from the early Oligocene of Wyoming. American Museum novitates ; no. 2485

7 p. : ill. ; 24 cm.Includes bibliographical references (p. 7)."Two specimens from early Oligocene deposits of the Flagstaff Rim area, Natrona County, Wyoming, represent a new species of beaver, Agnotocastor galushai. Although this is the oldest recorded form that can be definitely referred to the Castoridae, it is already similar to later species and sheds very little additional light on the ancestry of the family"--P. [1]