Three major carnivoran dispersal waves of filter-bridge type between Eurasia and North America are recognized in the late Neogene. The first is around 20 Ma, probably from 21 Ma to 19–18 Ma, during which intermittent dispersals might have occurred. The carnivorans migrating from Eurasia to North America included Cynelos, Ysengrinia, Amphicyon, Cephalogale, Phoberocyon, Ursavus, some small-sized mustelids, Potamotherium, an ancestral form of Edaphocyon, and Proailurus. The second wave occurred at about 7–8 Ma. The carnivorans migrating from Eurasia to North America included Indarctos, Agriotherium, Simocyon, Eomellivora, Plesiogulo, and Machairodus. The last wave took place in the early Pliocene ∼4 Ma. The Eurasian emigrants recorded in North America are Ursus, Parailurus, Lynx (?), Felis (?), Homotherium, and Chasmaporthetes. At about the same time Megantereon and Pannonictis migrated from North America to Eurasia.

Previous hypotheses for the origin and diversification of pinnipeds have followed a narrative approach based mostly on dispersalist (i.e., center of origin) explanations. Using an analytical approach, we present a testable hypothesis to explain the evolutionary biogeography of pinnipedimorphs (fur seals, sea lions, walruses, seals, and their fossil relatives) based on both dispersal and vicariant events in the context of a species-level phylogenetic framework. This integrated hypothesis considers many lines of evidence, including physical and ecologic factors controlling modern pinniped distributions, past geologic events related to opening and closing of seaways, paleoceanographic models, the improving pinniped fossil record, and pinniped phylogenetic analyses based on both morphologic and molecular data sets. Oceanic biogeographic regions and faunal provinces are defined and oceanic circulation patterns discussed with reference to the distribution of extant and fossil species. Paleobiogeographic hypotheses for each of the major pinniped lineages are presented using area cladograms and paleogeographic maps showing oceanographic and tectonic changes during successive intervals of the Cenozoic.

Our biogeographic hypothesis supports an eastern North Pacific origin for pinnipedimorphs during the late Oligocene coincident with initiation of glaciation in Antarctica. During the early Miocene, pinnipedimorphs remained restricted to the eastern North Pacific, where they began to diversify. Otariids (fur seals and sea lions) are first known from the late Miocene in the North Pacific, where they remained restricted until the late Pliocene. A transequatorial dispersal into the western South Pacific at this time preceded the rapid diversification of this group that occurred during the Pleistocene in the Southern Ocean. Odobenids (walruses) evolved in the North Pacific during the late early Miocene and underwent dramatic diversification in the late Miocene with later members of the odobenine lineage dispersing into the North Atlantic, most likely via an Arctic route. Extinct archaic phocoids, the desmatophocids, known only from the early to late Miocene, were confined to the eastern and western North Pacific. Phocids, although postulated here to have a North Pacific origin, are first known as fossils from the middle Miocene in the eastern and western North Atlantic region, as well as the Paratethys. Both monachine and phocine seals are distinct lineages beginning in the middle Miocene in the eastern and western provinces of the North Atlantic. During the late Miocene, phocids underwent a dramatic diversification. The early biogeographic history of phocine seals is centered in the Arctic and North Atlantic. Subsequent dispersal of phocines into the Paratethys and Pacific occurred during the Pleistocene. In contrast, monachine seals have a southern hemisphere center of diversity, especially the lobodontines of the Southern Ocean. Southern dispersal of this clade most likely occurred through the Neogene Central American Seaway prior to its closure in the mid-Pliocene. The pagophilic nature of extant phocine and lobodontine seals is largely a function of Pleistocene glacioeustatic events.

North American amphicyonid carnivorans are prominent members of the mid-Cenozoic terrestrial carnivore community during the late Eocene to late Miocene (Duchesnean to Clarendonian). Species range in size from <5 kg to >200 kg. Among the largest amphicyonids are Old and New World species of the genus Amphicyon: A. giganteus in Europe (18–∼15? Ma) and Africa, A. ingens in North America (15.9–∼14.2 Ma). Amphicyon first appears in the Oligocene of western Europe, surviving there until the late Miocene. Migration to Africa and North America takes place in the early Miocene. The genus occurs in the Arrisdrift fauna (Namibia) of southwest Africa, indicating migration south through the length of the African continent by the mid-Miocene. Its occurrence in Asia is problematical because of the tendency to place any moderately large Asian amphicyonid in the genus, and because of the fragmentary nature of many fossils.

Here I report the earliest North American occurrences of Amphicyon (18.8–∼17.5 Ma), assigning these individuals to a new and previously undescribed species, Amphicyon galushai, from early Hemingfordian sediments of western Nebraska and north-central Colorado. In the New World, small early Hemingfordian Amphicyon galushai is probably ancestral to larger late Hemingfordian A. frendens, and to the terminal and largest species of the genus, early to mid-Barstovian A. ingens. Diagnostic basicranial and dental traits place these species in the Amphicyonidae, and demonstrate a close relationship of the North American lineage to the type species of the genus, A. major, from Sansan, France.

Amphicyon galushai is known from a complete adult skull, a partial juvenile skull, three mandibles, and the isolated teeth and postcranial elements of ∼15 individuals, all from the early Miocene Runningwater Formation of western Nebraska. The species also is represented by a crushed rostrum from the Troublesome Formation, north-central Colorado.

Basicranial, dental, and postcranial anatomy distinguish A. galushai from its contemporary in the Runningwater Formation, the large digitigrade beardog Daphoenodon. The Runningwater Formation contains the last occurrence of Daphoenodon in North America and the first occurrence of Amphicyon; the overlap in stratigraphic ranges of these two carnivores provides a useful early Miocene biostratigraphic datum. The two amphicyonids occur together in the same quarries, associated with canid, mustelid, and rare procyonid carnivores, which are much smaller animals.

The North American species of Amphicyon (A. galushai, A. frendens, A. ingens) most likely adopted ecological roles similar to the large living felids (in particular, the lion Panthera leo). Their robust skeleton with powerful forelimbs, massive clawed feet, heavily muscled jaws with large canines, and a composite crushing/shearing dentition suggest a mobile predator that most likely stalked and ambushed prey from cover, overpowering its victims through sheer size and strength.

The ursid fossils collected from Saint Jacques include Pachycynodon tedfordi, new species, Amphicynodon sp., and Cephalogale sp. The distinctive features of Pachycynodon tedfordi are: short premolar series relative to molars, diastemata between c and p1 and among premolars very short or absent, distinct cingula on p1–p4, well-developed posterior accessory cuspids on p2–p4, long and narrow m1 with relatively high protoconid, metaconid lower than paraconid, and relatively long m2 without distinct paraconid.

Four genera (Amphicticeps, Amphicynodon, Pachycynodon, and Cephalogale) representing two subfamilies (Amphicynodontinae and Hemicyoninae) have been discovered in the Oligocene of Asia. The last three are genera common to Asia and Europe, and indicate migration. Based on the ursid and other mammalian fossils, the deposits at Loc. 77046 near Saint Jacques are determined as Oligocene in age, and those at Loc. 77046.5 are late early Oligocene. Migration of ursids between Asia and Europe occurred in the early Oligocene, and migration of several taxa from Asia to North America likely occurred later, in the late Oligocene or early Miocene.

Four new procyonids (Mammalia: Carnivora) are described in this paper. They include Bassaricyonoides stewartae, new genus and species, from the late Hemingfordian of Nevada, Bassaricyonoides phyllismillerae, new species, ?Edaphocyon palmeri, new species, both from the early Hemingfordian of Florida, and Parapotos tedfordi, new genus and species, from the Barstovian of Texas. Bassaricyonoides and Parapotos are the first known fossils of potosin procyonids. They support the monophyly of the Tribe Potosini, which includes the extant Bassaricyon and Potos, and indicate that the Potosini had diverged from the Procyonini by the early Miocene in North America. By the late Miocene, the Procyoninae had replaced the phlaocyonin and cynarctin canids as the dominant North American, small hypocarnivorans.

Borophaginae is the largest of the three subfamilies of the dog family Canidae, with some 66 species, spanning approximately 34 m.y. (Orellan to Blancan). Not surprisingly, this extensive radiation of canids includes a diverse array of dietary types, ranging from hypocarnivorous to hypercarnivorous and durophagous. The last 16 m.y. of borophagine history is dominated by hypercarnivorous forms that were the dominant doglike predators within their faunas. Because of their relatively robust skeletons and their resemblance to extant hyenas in craniodental morphology, many or most of these hypercarnivorous species, particularly those of the late Miocene and Pliocene, have been assumed as primarily scavengers rather than hunters. The classification of most hypercarnivorous borophagines as scavengers relegates them to much less important roles in the ecology and evolution of their respective communities than does a classification as hunters. Unlike hunters, scavengers are unlikely to influence the evolution of the animals they eat, and are expected to exist at relatively low densities as do the only extant scavenging carnivorans, brown (Parahyaena brunnea) and striped hyenas (Hyaena hyaena). Given the substantial fossil record of the Borophaginae, it seems unlikely that all or most of the hypercarnivorous forms were primarily scavengers. Moreover, if some hunted, the larger species might be expected to have done so in groups, as large canids hunt in packs today.

Here we examine possible foraging modes within the Borophaginae using morphometrics and two new approaches to estimating the typical prey size of extinct carnivores. The craniodental morphology of the Borophaginae is compared with that of the living Caninae and Hyaeninae (hyaenids exclusive of Proteles cristata, the aardwolf) based on measurements that reflect relative tooth size, jaw muscle leverage, rigidity of the dentary, and grinding versus slicing function of the teeth. The Borophaginae are found to be intermediate in morphology between the Caninae and Hyaeninae. Unlike hyaenids and like canines, they retain substantial postcarnassial molars. However, like hyaenids, the borophagines had significantly stronger jaws and enhanced jaw muscle leverage compared to other canids. Prey size is estimated for borophagines based on correlation between dentary height and typical prey size in living canids. These results are compared with those produced using a recently published energetic model that predicts that all carnivores larger than about 21 kg feed on prey as large or larger than themselves. The methods provide similar predictions, resulting in a list of 11 borophagines (all subtribes Aelurodontina and Borophagina) that probably consumed large prey.

Comparisons with extant hyaenids reveal that the sole hunter of large prey, the spotted hyena (Crocuta), differs from the two mainly scavenging species, the brown and striped hyenas, in being significantly larger, more abundant, and widespread. Moreover, morphometric comparisons indicate that spotted hyenas have a more hypercarnivorous dentition. Given this, it is expected that the largest, most common borophagines with the most reduced dental grinding areas hunted most of their food. Based on their craniodental morphology and abundance in the record, Epicyon saevus, E. haydeni, Borophagus secundus, Aelurodon ferox, and A. taxoides were hunters. Although it is clear that Aelurodon and Borophagus were more capable of grasping prey than are extant canids, no borophagine evolved sharp, curved c

New cranial and dental material from the early Hemingfordian of Florida and Nebraska permits recognition that Tephrocyon scitulus Hay, 1924, a poorly established taxon from the Texas Gulf Coast, belongs to the genus Osbornodon (Hesperocyoninae, Canidae). O. scitulus is a transitional species that partially fills a large morphological and stratigraphical gap within the Osbornodon clade. Compared to O. renjiei and O. sesnoni, O. scitulus possesses derived characters such as large frontal sinus, high sagittal crest, narrow infraorbital canal, short bulla, and broad premolars. O. scitulus differs from O. wangi in larger size and relatively wider P3 and shorter P4. On the other hand, O. scitulus is distinguishable from O. iamonensis and later species in its primitive characters such as rostrum not elongated, paroccipital process not expanded posteriorly, mastoid process not reduced, and p4 not differentially enlarged relative to p3.

The Screw Bean Local Fauna is the earliest Hemphillian fauna of the southwestern United States. The fossil remains occur in all parts of the informal Banta Shut-in formation, nowhere very fossiliferous. The formation is informally subdivided on the basis of stepwise fining and slowing deposition into Lower (least fossiliferous), Middle, and Red clay members, succeeded by the valley-filling, Bench member (most fossiliferous).

Identified Carnivora include: cf. Pseudaelurus sp. and cf. Nimravides catocopis, medium and large extinct cats; Epicyon haydeni, large borophagine dog; Vulpes sp., small fox; cf. Eucyon sp., extinct primitive canine; Buisnictis chisoensis, n. sp., extinct skunk; and Martes sp., marten. B. chisoensis may be allied with Spilogale on the basis of mastoid specialization. Some of the Screw Bean taxa are late survivors of the Clarendonian Chronofauna, which extended through most or all of the early Hemphillian. The early early Hemphillian, late Miocene age attributed to the fauna is based on the Screw Bean assemblage postdating oreodont and predating North American edentate occurrences, on lack of defining Hemphillian taxa, and on stage of evolution.

Chronostratigraphy and biochronology are the prime conceptual methods for relating biologic events to the geologic time scale. Chronostratigraphy is the dominant method applied in the oceanographic-marine realm, and biochronology is the dominant method for the terrestrial realm. These concepts were conceived in the early half of the 20th century, and major advances in both occurred during the latter half of the 20th century. Historical development of both chronostratigaphy and biochronology is briefly reviewed, and it is concluded that the early definition and application of biochronology is tainted by reference to and inference from biostratigraphy. It is proposed that biochronology be redefined as the organization of geologic time according to the irreversible process of organic evolution, following the characterization and application by Berggren and Van Couvering (1978, G.V. Cohee, M.F. Glaessner, and H.D. Hedberg [editors], Contributions to the geologic time scale: 39–55. Tulsa, OK: American Association of Petroleum Geologists). The new term “chronostratigraphic marker” is proposed and defined as any chronologically significant event (biologic, isotopic, isotopic-ratio, or paleomagnetic), recorded in a stratigraphic sequence, that can be directly related to and/or tied to any other chronostratigraphic marker. According to definitions given herein, a biochronologic event can become a chronostratigraphic marker, but only when tied to a discrete stratigraphic sequence and related to other stratigraphic sequences and/or chronostratigraphic markers.

The terms and concepts “datum event”, “land mammal age”, “stage of evolution”, and “appearance event ordination” are discussed and defined. A datum event is defined as any chronostratigraphic marker. Land mammal ages, along with European Neogene and Paleogene mammal units, are considered biochronologic entities; they are defined as relatively short intervals of geologic time that can be recognized and distinguished from earlier and later such units (in a given region or province) by a characterizing assemblage of mammals. Stage of evolution is a very basic biochronologic concept defined as the chronologic ordering of faunal assemblages based on morphological (evolutionary) differences observed in members of a single, well-established phyletic lineage. Appearance event ordination is a new tool of biochronology. It is defined as ordering the appearance of fossil mammal genera by multivariate analysis, using overlapping (conjunctive) and nonoverlapping (disjunctive) range distributions in large sets of data.

Studies of fossil remains of age-diagnostic land mammals have allowed recognition of assemblages of late Uintan, early and late Arikareean, and early Hemingfordian (late middle Eocene, early Oligocene to early Miocene) age in the Sespe Formation and equivalent marine formations of the northern Peninsular Ranges Provinces and western Transverse Ranges in Los Angeles, Orange, Santa Barbara, and Ventura counties, southern California. Recent fossil recovery efforts have resulted in the recognition of new land mammal assemblages in the Santa Ana Mountains and San Joaquin Hills of Orange County, the Santa Monica Mountains of Los Angeles County, and Simi Valley, Ventura County. The late Arikareean fauna appears to represent a new assemblage that has not been recognized previously in the fossil land mammal record of southern California. The presence of a late Uintan assemblage near the base of the undifferentiated Sespe and Vaqueros formations (S/V) in the northern Santa Ana Mountains of Orange County suggests that the base of the unit is similar in age to the base of the Sespe Formation in the Simi Valley area. The top of the S/V in the northern Santa Ana Mountains and San Joaquin Hills of Orange County and in the Santa Monica Mountains of Los Angeles County is approximately 10.4 million years younger than the top the Sespe Formation in the Simi Valley area, at South Mountain, and along Oak Ridge in Ventura County. In the northern Santa Ana Mountains and the Santa Monica Mountains, early Hemingfordian land mammal assemblages occur stratigraphically below late Hemingfordian land mammal assemblages in the overlying marine and continental Topanga Formation.

Significant mammalian faunas of Pliocene (Blancan) and early Pleistocene (early and medial Irvingtonian) age are known from the Rio Grande and Gila River valleys of New Mexico. Fossiliferous exposures of the Santa Fe Group in the Rio Grande Valley, extending from the Española basin in northern New Mexico to the Mesilla basin in southernmost New Mexico, have produced 21 Blancan and 6 Irvingtonian vertebrate assemblages; three Blancan faunas occur in the Gila River Valley in the Mangas and Duncan basins in southwestern New Mexico. More than half of these faunas contain five or more species of mammals, and many have associated radioisotopic dates and/or magnetostratigraphy, allowing for correlation with the North American land-mammal biochronology. Two diverse early Blancan (4.5–3.6 Ma) faunas are known from New Mexico, the Truth or Consequences Local Fauna (LF) from the Palomas basin and the Buckhorn LF from the Mangas basin. The former contains five species of mammals indicative of the early Blancan: Borophagus cf. B. hilli, Notolagus lepusculus, Neotoma quadriplicata, Jacobsomys sp., and Odocoileus brachyodontus. Associated magnetostratigraphic data suggest correlation with either the Nunivak or Cochiti Subchrons of the Gilbert Chron (4.6–4.2 Ma), which is in accord with the early Blancan age indicated by the mammalian biochronology. The Truth or Consequences LF is similar in age to the Verde LF from Arizona, and slightly older than the Rexroad 3 and Fox Canyon faunas from Kansas. The Buckhorn LF has 18 species of mammals, including two rodents typical of the early Blancan, Mimomys poaphagus and Repomys panacaensis. The Buckhorn LF also is similar in age to the Verde LF and has affinities with the Panaca LF from Nevada. Although the Buckhorn and Truth or Consequences LFs have few taxa in common, the similarities of both faunas with the Verde LF suggest they are close in age.

Eight faunas from the central and southern Rio Grande Valley are medial Blancan in age (3.6–2.7 Ma), including the Pajarito and Belen faunas from the Albuquerque basin, the Arroyo de la Parida LF from the Socorro basin, the Cuchillo Negro Creek and Elephant Butte Lake LFs from the Engle basin, the Palomas Creek LF from the Palomas basin, the Hatch LF from the Hatch-Rincon basin, and the Tonuco Mountain LF from the Jornada basin. These faunas are characterized by the presence of taxa absent from early Blancan faunas, including Geomys (Nerterogeomys) paenebursarius, Equus cumminsii, E. scotti, and Camelops, and the absence of South American immigrant mammals found in late Blancan faunas. The Pajarito LF is directly associated with a pumice dated at 3.1 Ma. The Cuchillo Negro Creek and Elephant Butte Lake LFs are in close stratigraphic association with a basalt flow of 2.9 Ma. Magnetostratigraphy constrains the age of the Tonuco Mountain LF between 3.6 and 3.0 Ma.

The Mesilla A fauna from the Mesilla basin and the Pearson Mesa LF from the Duncan basin are late Blancan in age (2.7–2.2 Ma). Both record the association of Nannippus with a South American immigrant, Glyptotherium from Mesilla A and Glossotherium from Pearson Mesa, restricting their age to the interval after the beginning of the Great American Interchange at about 2.7 Ma and before the extinction of Nannippus ca. 2.2 Ma. Magnetostratigraphy further constrains the Mesilla A and Pearson M

Information on Mexico's middle Miocene mammal record improves understanding of the southern extent, makeup, and relationships of North American Tertiary faunas. The Hemingfordian–Barstovian combined assemblage (= HBCA) in Mexico records 6 orders, 17 families, and 35 genera, each represented probably by a single species known from sites in Baja California Norte and Sur (one each), Sonora (two), Aguascalientes (one), Oaxaca (three), and Chiapas (one). Barstovian diversity is nearly triple that of the Hemingfordian. The Barstovian Oaxacan subassemblage is by far the largest. This combined assemblage includes most of the orders and a little over a third of the families known to occur in North America for this interval. The better Tertiary post-Barstovian record does not include Clarendonian age sites, and has no representation in southern Mexico.

The HBCA consists mainly of herbivores and has very few carnivorans. The Barstovian equids from Southeastern Mexico include an ancestral merychippine coexisting with hipparionines and pliohippines. The coexistence of two derived lineages implies either repeated southward migration of equid species from temperate North America shortly after their origination or that some equid differentiation took place in tropical Middle America. Further work may clarify this issue. The HBCA shows strict North American affinities. Seven families and 16 genera have their southernmost occurrence in Mexico. The putative recent discovery in Peru of North American Clarendonian or older mammals may indicate that at least the southward migrating component of the Great American Faunal Interchange occurred earlier than currently thought. Three of the four families recorded in Peru occur in the Barstovian of Southeastern Mexico, thus lending support to this contention.

We describe Paratoceras tedfordi, a new species of Protoceratidae from early Miocene amber-bearing sands near Simojovel, Chiapas, southern Mexico. The holotypic cranium weakly expresses maxillary plates, supraorbital rugosities, and a median occipital projection as in the type of Paratoceras wardi, and is interpreted as a female. Its short facial region, elongate premolars, and brachydont molars place it among the Protoceratinae, not Synthetoceratinae. We also describe new cranial and the first postcranial material of Prosynthetoceras texanus from Alum Bluff and Thomas Farm sites in Florida. Incorporating data from these new specimens, we consider highlights of protoceratid adaptive morphology including their elaborate male ossicones, tapirlike proboscis, brachydont to mesodont dentition, and limb features and proportions. We suggest that progressive protoceratids may be seen as ecological analogues of the Bushbuck of South Africa, a forest-adapted browser. Each of the three groups of horned Protoceratidae speciated allopatrically along latitudinal lines, with the northern branch becoming extinct earlier than its southern sister. Their greater proclivity toward survival in tropical latitudes explains the importance of Protoceratidae in the Gulf Coastal Plain during the Miocene, and evident higher abundance of Paratoceras in Central America.

Exceptionally well-preserved partial skeletal remains representing a minimum of six individuals of an oreodont are described from the White Springs Local Fauna, Columbia County, northern Florida. Although oreodonts are very common from classic Oligocene and early Miocene deposits in the western United States, this group is poorly represented from Florida. The White Springs oreodont pertains to a new species, Mesoreodon floridensis, and is derived, particularly in the development of the auditory bulla, relative to more primitive, closely related species such as Merycoidodon culbertsoni, the latter of which is well known from the badlands of the western United States. Mesoreodon floridensis differs from most other species assigned to this genus in the relative development of the nasal region, possible presence of a facial vacuity, configuration of the preorbital fossa, relatively simple occipital and zygomatic morphology, and imbricated premolar morphology. Based on the associated faunal remains and age determinations, M. floridensis is late early Arikareean (Ar2) in age, ca. 25–24 million years old, and occurs in an interval not well represented in the classic Arikareean sequence of western Nebraska. A mounted skeleton of M. floridensis, on exhibition, is also described.

The morphology and dimensional parameters of the cranium and upper and lower cheek tooth dentition of the early Barstovian aged three-toed horse, Merychippus insignis, the genotypic species, are analyzed based on specimens from Echo Quarry in the Olcott Formation of western Nebraska. Specimens of early Barstovian age from the Trinity River Pit 1 quarry, Texas, and of late Barstovian age from Deep Creek, Nebraska, are utilized to corroborate the association of upper and lower dentitions of the Echo Quarry sample to Merychippus insignis. A revised definition of Cormohipparion is utilized. Cormohipparion goorisi is characterized on the basis of cranial and dental information based on material from Trinity River Pit 1, Texas (early Barstovian). Based on these species, Merychippus and Cormohipparion are distinctly different taxa.

The earliest record of the microtine rodent genus Mimomys is from West Siberia, where, over 5 million years ago, it evolved from Promimomys. From western Asia, early Mimomys dispersed both east and west (to North America and to Europe), arriving at about the same time in both areas as a slightly larger and more evolved form that is essentially identical in both continents. Different species names are applied, as they obviously represent the beginnings of geographically separate lineages.

The immigration of Mimomys to North America marks the beginning of the Blancan Mammal Age by original definition. The earliest dated North American record is the Upper Alturas Fauna of California, which is well dated by paleomagnetic stratigraphy, tephra “fingerprinting”, and potassium–argon dating at 4.8 Ma. Lindsay et al. (1999) have supported this age by paleomagnetic stratigraphy in two areas of Nevada. One other known fauna, the Maxum fauna of Contra Costa County, California, contains immigrant Mimomys that may be slightly older, but is not dated.

Dispersal of the temperate-climate genus Mimomys between Eurasia and North America was through the Beringian Faunal Region, near the latitude of the Arctic Circle, and later intercontinental continuity of the genus was severely restricted by climate, not water. Other microtine rodents, more tolerant of cooler latitudes, were able to cross the Bering land area and thus integrate the biochronologies of the two continents, but the genus Mimomys is of little use in intercontinental correlation during most of the Pliocene.

Eurasia and North America contain many faunal regions, and the temperate United States comprises at least two, separated by the Rocky Mountains. Each faunal region has, to an extent limited by its isolation, unique faunas and a different historic biochronology. Although the first Mimomys immigrants to North America and Europe were very similar, the genus evolved independently on the separate continents for the next 3.4 m.y., producing species, subgenera, and ultimately, new genera dramatically different in the two areas. During this isolation, separate lineages in the United States resulted in the subgenus M. (Cosomys) and the genus Ophiomys in the Western Faunal Region and in the subgenus M. (Ogmodontomys) and the genus Hibbardomys in the Eastern Faunal Region.

Although also climatically constrained, the barrier to dispersal between these two faunal regions of the United States was much less rigorous than in Beringia. Several times taxa dispersed along two documented routes between the Eastern and Western Faunal Regions of the United States: through Yellowstone Pass in western Wyoming and around the southern end of the Rocky Mountains through Arizona and New Mexico. These faunal interchanges are useful in correlating the two regional biochronologies, and times of exchange correlate with the climate changes that made the Rocky Mountains, or the region to the south of it, habitable by temperate Mimomys.

About 1.3 Ma, global warming again permitted Mimomys to disperse through Beringia. At or slightly before this second immigration of Mimomys, the descendants of the first immigration had become extinct or had evolved into forms no longer conforming to the

New material of dasyurids, peramelids, phalangerids, pseudocheirids, burramyids, ektopodontids, and vombatids from the early Pliocene Hamilton fauna of Victoria, Australia, includes a new perameloid species and the first record of vombatids in the Hamilton fauna. The earlier interpretation of the assemblage as representing a rain forest fauna is confirmed.

Partial skeletons, including jaw fragments, collected by Richard H. Tedford and colleagues at Lake Pinpa in the Callabonna Basin of northeastern South Australia, represent a new species of the putative wynyardiid marsupial Muramura. The new species is slightly smaller and more gracile than its congener M. williamsi from the roughly contemporaneous Etadunna Formation of the Lake Eyre Basin.

Since Woodburne (1969) analyzed the three diprotodontid specimens then known from the Mio-Pliocene Beaumaris locality in Victoria, Australia, three more specimens of that group have been recognized. Included among them is a lower jaw, referred here to Kolopsis cf. K. torus, originally thought to be from Queensland. Strong evidence, however, indicates it is from Beaumaris. Reanalysis of the six diprotodontid specimens now known clearly establishes that two diprotodontids occur at Beaumaris, Zygomaturus gilli and K. cf. K. torus. On the basis of the K. cf. K. torus jaw supposedly from Queensland, the Beaumaris local fauna is interpreted to be contemporaneous or slightly older than the Alcoota local fauna from the Northern Territory.

A mid-Tertiary rock sequence at the Tieersihabahe locality from the Ulungur River area in the northern Junggar Basin, Xinjiang Province, China, is described. The study introduces three late Oligocene/Early Miocene faunas from the continuous section of the “Ulunguhe” and Suosuoquan formations within the sequence, and discusses the age determination, faunal correlation, and existing problems concerning the formations and faunas. The “Ulunguhe” fauna at the Tieersihabahe locality is late Oligocene in age, correlative to the Taben Buluk fauna. The 99005 fauna is probably Oligocene–Miocene transitional. The Suosuoquan fauna is regarded as early Miocene, so the Oligocene/Miocene boundary would be contained in the continuous section at the Tieersihabahe section.

Cenozoic terrestrial deposits with a dense fossil record are widespread in China. At least 126 genera of rodents, belonging to 25 families and subfamilies, are known from the Neogene. Geographical distribution of the fossil rodents indicates that zoogeographic differentiation in China was already quite distinct and faunal provinces similar to the present day Palearctic Realm in North China and to the Oriental Realm in South China existed throughout Neogene time. An initial phase in development of the present Oriental region emerged by the early Miocene in southeastern Asia. Faunas in northern China were Holarctic in character and showed greater similarity in composition to Europe than to North America. Apparently, immigration and dispersal of rodents in the Holarctic Region repeatedly took place via the Bering Landbridge during the Neogene. Interchange of rodents between Asia and Europe tended to gradually increase during the Neogene, whereas it declined between Asia and North America after the late Miocene.

Thirty-five years ago Dick Tedford and Len Radinsky collected the remains of three individuals of a new gerbil in the hill country of Afghanistan. Tedford's gerbil is a new, large species of a widespread late Neogene genus, Abudhabia. The material is extraordinarily complete, including three crania and many of the postcrania. The extinct taxon is clearly a gerbil based on dental and cranial features, while it has a relatively underived basicranium. The long hind limb proportions appear strongly derived. The bulla is enlarged and the mastoid is little inflated, not as inflated as in many gerbils. The fossil form is a primitive taterilline and suggests homoplasy in ear structure and dentition among modern taxa.

A recently discovered tooth of the hominid primate Griphopithecus suessi Abel, 1902 is only the fifth tooth known of the species, and the first upper M3. All five teeth are from the locality known as Sandberg, near Devínska Nová Ves (formerly known as Neudorf an der March), in the northwestern suburban part of Bratislava, Slovakia. The deposit in which the locality occurs is a transgressive sequence of nearshore marine sediments that are Upper Badenian in terms of the central Paratethyan marine biostratigraphy. The locality has also yielded a land mammal fauna of modest diversity that corresponds to earliest MN6 of the European land mammal biochronology. As earliest MN6, Griphopithecus suessi is among the earliest known hominids in Europe. Since Abel's description in 1902, the species has had a peripatetic taxonomic and nomenclatural history, but most recently was returned to Abel's genus Griphopithecus, which requires that it also be returned to Abel's species G. suessi, the type species of the genus.

Mimotricentes tedfordi, new species, is a small arctocyonid mammal whose type specimen is from the Tiffanian (late Paleocene) Laudate local fauna, found at the base of informal member 4b of the Goler Formation, southwesternmost Great Basin, Kern County, California. The type specimen is a fragmentary maxilla with P4–M3. Smaller than morphologically similar taxa based on upper teeth, M. tedfordi is characterized by a large, projecting parastyle on M1 and M2, by a proliferation of mesostyle-like cusps on the molars, by lack of complete cingula around the lingual bases of the molar protocones, and by somewhat crenulated enamel surfaces on the posterior slope of P4 and possibly the molars when unworn. M. tedfordi is most similar to, but 20% smaller than, certain specimens formerly identified as Chriacus sp. from the earliest Tiffanian of Douglass Quarry, eastern Crazy Mountain Basin, Montana. Also, newly collected specimens from the Goler Formation of other mammalian taxa show strong Tiffanian affinities. As a whole, these data support a Tiffanian age for the Laudate local fauna, but require that an unnamed anisonchine periptychid similar to Conacodon be considered a Tiffanian relict.

The late Paleocene phosphates of the Ouled Abdoun Basin in Morocco have yielded the skull of a new genus and species of side-necked turtle, Phosphatochelys tedfordi. Phosphatochelys is a pelomedusoid pleurodire belonging to the Family Bothremydidae Baur, 1891, based on these characters: (1) precolumellar fossa absent, (2) condylus occipitalis consisting only of exoccipitals, (3) foramen stapedio-temporale not visible in dorsal view and very close to foramen nervi trigemini, (4) eustachian tube and stapes separated by bone, (5) incisura columellae auris closed, and (6) exoccipital contacts quadrate. Within the Bothremydidae, Phosphatochelys is a member of the group containing Azabbaremys, Taphrosphys, Nigeremys, and Arenila, because it has a dorsally arched palate and an open postorbital wall.