Cormohipparion occidentale complex

138 p. : ill., map ; 26 cm.Includes bibliographical references (p. 134-138).Study of the materials in the American Museum of Natural History that pertain to the taxon Cormohipparion occidentale Skinner and MacFadden (1977) reveals that at least six species are represented. This is based on data from the cranium, upper dentition, lower dentition, and mandible. The taxa embrace a period of time from about 12.5 Ma to 10 Ma. Major sites or faunas include the Dove Spring Formation (medial Clarendonian, California; Burge Local Fauna (early Clarendonian, Nebraska); Minnechaduza Fauna, Nebraska; MacAdams Quarry, Texas (early medial Clarendonian); Gidley Horse Quarry (late medial Clarendonian, Texas); XMas-Kat, Hans Johnson, and Machaerodus quarries (late medial Clarendonian, Nebraska); and Ash Hollow Formation (late medial Clarendonian, South Dakota). The name Cormohipparion occidentale is restricted to the larger of two species that occur contemporaneously in medial Clarendonian sites in Nebraska and, alone, at the Ed Ross Ranch Quarry, South Dakota. The second species in the XMas-Kat and related quarries is assigned to Cormohipparion matthewi, n.sp. A taxon from the Burge Local Fauna is assigned to Cormohipparion merriami, n.sp. Another taxon from the Burge Local Fauna is assigned to Cormohipparion johnsoni, n.sp. Materials from the Texas sites are allocated as Cormohipparion fricki, n.sp., and Cormohipparion skinneri, n.sp., from the MacAdams Quarry and Gidley Horse Quarry, respectively. Cormohipparion fricki, n.sp., also is represented in the Minnechaduza Fauna, Nebraska. Cormohipparion is restricted geographically to North America. Based on this review, Cormohipparion johnsoni, n.sp., is the most plesiomorphic species of the C. occidentale group of taxa. Cormohipparion quinni is a plausible ancestor (sister-taxon) for the C. occidentale group, but also persisted with it until about 12 Ma. During their radiation, elements of the C. occidentale group demonstrate an increase in upper cheek tooth crown height and complexity of the enamel pattern, as well as an increase in overall cranial size, with each species showing its own mosaic of parameters. The interval of 12.5-10 m.y. witnessed the initiation of a period of climatic cooling and an eventual expansion of vegetation communities toward more open associations, in part showing an increase in grassy areas. Apparently, the C. occidentale group developed and maintained a mixed-feeding adaptation to these conditions, even though it had evolved very hypsodont cheek teeth by about 10 Ma (C. occidentale, s.s.; C. skinneri, n.sp.). Cormohipparion johnsoni, n.sp., and C. merriami, n.sp., are followed by C. fricki, n.sp., at about 12-11.5 Ma, which demonstrates an increased crown height and complexity of the upper cheek teeth along with the persistence of a functional dP1 into the adult condition. At least in C. fricki, n.sp., and likely also C. merriami, n.sp., the pre- and postfossettes of P2 commonly were confluent. All of these features are to be found in early Pannonian C members of Hippotherium of the Old World, and it is likely that a taxon such as C. fricki, n.sp., was associated with the Old World dispersal event that resulted in the presence of H. primigenium. A specimen of Cormohipparion sp. from deposits about 12 Ma old in California shows the proper morphology (enhanced by a significant increase in fossette complexity) to be a possible member of the dispersal population prior to its exit to the Old World at about 11 Ma. Subsequent North American species of the Cormohipparion occidentale group lived from about 11 Ma to 10 Ma and convergently approach (but do not equal) the enamel pattern complexity found in Hippotherium primigenium but surpass it in upper cheek tooth crown height, in the almost complete loss of dP1, and in a diminished frequency of confluence of the pre- and postfossetttes in P2. Two of these species, C. occidentale, s.s., and C. skinneri, n.sp., apparently populated a more northern (Great Plains) versus a southern (Texan) district, with C. occidentale, s.s., being sympatric with the (?secondarily) smaller C. matthewi, n.sp. The sample of C. occidentale, s.s., from the XMas-Kat quarries of Nebraska differs somewhat in a few cranial and dental parameters from samples from the Machaerodus and Hans Johnson quarries. Whereas the material from the XMas-Kat and Machaerodus quarries seems contemporaneous on geological grounds, the age of the sample from the Hans Johnson Quarry is not as securely dated. It is possible that the cranial differences (mainly the size of the preorbital fossa) and dental parameters (the persistence of a small and apparently functionally insignificant dP1 in adult female, but not male, crania) are variations in a contemporaneous but somewhat polymorphic population. Alternatively, it is possible that the Hans Johnson sample, at least, may be chronologically somewhat older than that from the Xmas-Kat quarries and that the morphological differences represent in part a more plesiomorphic condition for its specimens

"South American" marsupials from the late cretaceous of North America and the origin of marsupial cohorts

Newly described marsupial specimens of Judithian (late Campanian) and Lancian (Maastrichtian) age in the western interior of North America (Wyoming to Alberta) have dental morphologies consistent with those expected in comparably aged sediments in South America (yet to be found). Three new Lancian species are referable to the didelphimorphian Herpetotheriidae, which suggests that the ameridelphian radiation was well under way by this time. The presence of a polydolopimorphian from Lancian deposits with a relatively plesiomorphic dental morphology and an additional polydolopimorphian taxon from Judithian deposits with a more derived molar form indicate that this lineage of typically South American marsupials was diversifying in the Late Cretaceous of North America. This study indicates that typical South American lineages (e.g. didelphimorphians and polydolopimorphians) are not the result of North American peradectian progenitors dispersing into South America at the end of the Cretaceous (Lancian), or at the beginning of the Paleocene (Puercan), and giving rise to the ameridelphian marsupials. Instead, these lineages, and predictably others as well, had their origins in North America (probably in more southerly latitudes) and then dispersed into South America by the end of the Cretaceous. Geophysical evidence concerning the connections between North and South America in the Late Cretaceous is summarized as to the potential for overland mammalian dispersal between these places at those times. Paleoclimatic reconstructions are considered, as is the dispersal history of hadrosaurine dinosaurs and boid snakes, as to their contribution to an appraisal of mammalian dispersals in the Late Cretaceous. In addition, we present a revision of the South American component of the Marsupialia. One major outcome of this process is that the Polydolopimorphia is placed as Supercohort Marsupialia incertae sedis because no characteristics currently known from this clade securely place it within one of the three named marsupial cohorts.Fil: Case, Judd A.. Saint Mary's College of California; Estados UnidosFil: Goin, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico de Paleontología de Vertebrados; ArgentinaFil: Woodburne, Michael O.. Museum of Northern Arizona; Estados Unido

Tertiary monotreme

11 p. : ill., map ; 26 cm.Includes bibliographical references (p. 11)."Remains of a new genus and species of fossil, ornithorhynchid monotreme are described. The specimens were recovered from Miocene deposits in South Australia and are part of the Ngapakaldi and equivalent aged faunas in this region. The fossil genus represents the oldest record of the group in Australia and begins to fill a large gap in our understanding of the evolution of the Monotremata"--P. [1]

Palaeogeography and palaeoenvironments of northern Patagonia from the Late Cretaceous to the Miocene : The Palaeogene Andean gap and the rise of the North Patagonian High Plateau

We summarize the geotectonic history of the southern (mostly Patagonian) Andean Cordillera, and its possible influence on the regional expression of global climates, biogeography, and important aspects of mammalian evolution in South America. The northern Patagonian segment of the Andes contrasts with neighbouring sections in that, during Palaeogene times, there was a transform margin stage; this influenced the Andean climate in addition to global climate changes. This segment underwent alternating subduction and transform episodes that suggest the existence of a proto-Andes and an Oligocene Andean gap for the San Carlos de Bariloche area. Coeval with this gap (and at the backarc region of this segment), the 1200-1500m uplift of the Northern Patagonian Massif took place, resulting in an altiplano (high plateau), or Northern Patagonian High Plateau (NPHP), of 100000km2, which dominated northern Patagonia during the Oligocene. It is estimated that, by these times, climate in the NPHP was humid and seasonally cool, in contrast to the seasonally more uniform, humid climates of the lower lands peripheral to it. The NPHP may have acted as a biogeographical barrier between central and southern Patagonia, on one side (as part of the Austral Biogeographical Kingdom), and the rest of South America (Holotropical Kingdom) on the other. The most important Paleogene mammalian turnover transpired at the Early Oligocene, concomitantly with the full opening of the Drake Passage and associated global cooling. The latitudinal climate gradient that began at the Eocene-Oligocene transition affected sharply the entire Patagonian region, an effect that was enhanced by the uplift of the NPHP.Se resume la historia geotectónica del sector sur (principalmente Patagonia) de la Cordillera Andina y su posible influencia en la expresión regional de los climas globales, biogeografía e importantes aspectos de la evolución de los mamíferos en Sud América. El sector norte de los Andes Patagónicos contrasta con los sectores vecinos en que durante el Paleógeno existió un estadio de margen transformante; esto influenció el clima en los Andes en forma adicional a los cambios climáticos globales. Este segmento fue sometido a la alternancia de episodios de subducción y margen transformante, que sugieren la existencia de un proto-Andes y la existencia de un gap Oligoceno de los Andes para el área de San Carlos de Bariloche. Contemporáneo a este gap (y en la región del retroarco de este segmento) tiene lugar el levantamiento del Macizo Norpatagónico a una altura de 1200–1500 m, dando como resultado la formación de un altiplano (plateau elevado), o Plateau Elevado del Macizo Norpatagónico (NPHP), con una superficie de 100.000 km2 la cual dominaba el norte de Patagonia durante el Oligoceno. Se estima que para esos tiempos, el clima en el NPHP fue húmedo con estaciones frías, en contraste con el clima estacionalmente más uniforme y húmedo de las tierras bajas de la periferia. El NPHP pudo haber actuado como una barrera biogeográfica entre Patagonia sur y central por un lado (como parte del Reino biogeográfico Austral) y por otro, con el resto de Sud América (Reino Holotropical). El ‘turnover’ más significativo para los mamíferos ocurrió en el Oligoceno Temprano, concomitante con la apertura del Pasaje de Drake y el enfriamiento global asociado. El gradiente latitudinal del clima que se inicio en la transición Eoceno-Oligoceno afectó profundamente la región Patagónica, un efecto que fue realzado por el levantamiento del NPHP.Centro de Investigaciones GeológicasFacultad de Ciencias Naturales y MuseoCentro de Estudios Parasitológicos y de Vectore

Palaeogeography and palaeoenvironments of northern Patagonia from the Late Cretaceous to the Miocene : The Palaeogene Andean gap and the rise of the North Patagonian High Plateau

We summarize the geotectonic history of the southern (mostly Patagonian) Andean Cordillera, and its possible influence on the regional expression of global climates, biogeography, and important aspects of mammalian evolution in South America. The northern Patagonian segment of the Andes contrasts with neighbouring sections in that, during Palaeogene times, there was a transform margin stage; this influenced the Andean climate in addition to global climate changes. This segment underwent alternating subduction and transform episodes that suggest the existence of a proto-Andes and an Oligocene Andean gap for the San Carlos de Bariloche area. Coeval with this gap (and at the backarc region of this segment), the 1200-1500m uplift of the Northern Patagonian Massif took place, resulting in an altiplano (high plateau), or Northern Patagonian High Plateau (NPHP), of 100000km2, which dominated northern Patagonia during the Oligocene. It is estimated that, by these times, climate in the NPHP was humid and seasonally cool, in contrast to the seasonally more uniform, humid climates of the lower lands peripheral to it. The NPHP may have acted as a biogeographical barrier between central and southern Patagonia, on one side (as part of the Austral Biogeographical Kingdom), and the rest of South America (Holotropical Kingdom) on the other. The most important Paleogene mammalian turnover transpired at the Early Oligocene, concomitantly with the full opening of the Drake Passage and associated global cooling. The latitudinal climate gradient that began at the Eocene-Oligocene transition affected sharply the entire Patagonian region, an effect that was enhanced by the uplift of the NPHP.Se resume la historia geotectónica del sector sur (principalmente Patagonia) de la Cordillera Andina y su posible influencia en la expresión regional de los climas globales, biogeografía e importantes aspectos de la evolución de los mamíferos en Sud América. El sector norte de los Andes Patagónicos contrasta con los sectores vecinos en que durante el Paleógeno existió un estadio de margen transformante; esto influenció el clima en los Andes en forma adicional a los cambios climáticos globales. Este segmento fue sometido a la alternancia de episodios de subducción y margen transformante, que sugieren la existencia de un proto-Andes y la existencia de un gap Oligoceno de los Andes para el área de San Carlos de Bariloche. Contemporáneo a este gap (y en la región del retroarco de este segmento) tiene lugar el levantamiento del Macizo Norpatagónico a una altura de 1200–1500 m, dando como resultado la formación de un altiplano (plateau elevado), o Plateau Elevado del Macizo Norpatagónico (NPHP), con una superficie de 100.000 km2 la cual dominaba el norte de Patagonia durante el Oligoceno. Se estima que para esos tiempos, el clima en el NPHP fue húmedo con estaciones frías, en contraste con el clima estacionalmente más uniforme y húmedo de las tierras bajas de la periferia. El NPHP pudo haber actuado como una barrera biogeográfica entre Patagonia sur y central por un lado (como parte del Reino biogeográfico Austral) y por otro, con el resto de Sud América (Reino Holotropical). El ‘turnover’ más significativo para los mamíferos ocurrió en el Oligoceno Temprano, concomitante con la apertura del Pasaje de Drake y el enfriamiento global asociado. El gradiente latitudinal del clima que se inicio en la transición Eoceno-Oligoceno afectó profundamente la región Patagónica, un efecto que fue realzado por el levantamiento del NPHP.Centro de Investigaciones GeológicasFacultad de Ciencias Naturales y MuseoCentro de Estudios Parasitológicos y de Vectore

The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens

The biotic and geologic dynamics of the Great American Biotic Interchange are reviewed and revised. Information on the Marine Isotope Stage chronology, sea level changes as well as Pliocene and Pleistocene vegetation changes in Central and northern South America add to a discussion of the role of climate in facilitating trans-isthmian exchanges. Trans-isthmian land mammal exchanges during the Pleistocene glacial intervals appear to have been promoted by the development of diverse non-tropical ecologies

New Early Eocene Mammalian Fauna from Western Patagonia, Argentina

Two new fossil mammal localities from the Paleogene of central-western Patagonia are preliminarily described as the basis for a new possible biochronological unit for the early Eocene of Patagonia, correlated as being between two conventional SALMAs, the Riochican (older) and the Vacan subage of the Casamayoran SALMA. The mammal-bearing strata belong to the Middle Chubut River Volcanic-Pyroclastic Complex (northwestern Chubut Province, Argentina), of Paleocene-Eocene age. This complex includes a variety of volcaniclastic, intrusive, pyroclastic, and extrusive rocks deposited after the K-T boundary. Geochronological data taken from nearby volcanic deposits that underlie and overlie the mammal-bearing levels indicate that both faunas are of late early Eocene age (Ypresian-Lutetian boundary). In addition to more than 50 species of mammals, including marsupials, ungulates, and xenarthrans, two lower molars are the oldest evidence of bats in South America. Paleobotanical and palynological evidence from inferred contemporary localities nearby indicate subtropical environments characterized by warm and probably moderately humid climate. Remarkably, this new fauna is tentatively correlated with Eocene mammals from the La Meseta Formation in the Antarctic Peninsula. We conclude that the two localities mentioned above are part of a possible new biochronological unit, but the formal proposal of a new SALMA awaits completion of taxonomic analysis of the materials reported upon here. If the La Meseta fauna is correlated biochronologically to western Patagonia, this also suggests a continental extension of the biogeographic Weddelian Province as far north as central-western Patagonia.Facultad de Ciencias Naturales y Muse

Formation of the Isthmus of Panama

The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed manymillions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways,withformationof theIsthmus of Panama sensustricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.Facultad de Ciencias Naturales y Muse

A Phylogeny and Timescale for the Evolution of Pseudocheiridae (Marsupialia: Diprotodontia) in Australia and New Guinea

Pseudocheiridae (Marsupialia: Diprotodontia) is a family of endemic Australasian arboreal folivores, more commonly known as ringtail possums. Seventeen extant species are grouped into six genera (Pseudocheirus, Pseudochirulus, Hemibelideus, Petauroides, Pseudochirops, Petropseudes). Pseudochirops and Pseudochirulus are the only genera with representatives on New Guinea and surrounding western islands. Here, we examine phylogenetic relationships among 13 of the 17 extant pseudocheirid species based on protein-coding portions of the ApoB, BRCA1, ENAM, IRBP, Rag1, and vWF genes. Maximum parsimony, maximum likelihood, and Bayesian methods were used to estimate phylogenetic relationships. Two different relaxed molecular clock methods were used to estimate divergence times. Bayesian and maximum parsimony methods were used to reconstruct ancestral character states for geographic provenance and maximum elevation occupied. We find robust support for the monophyly of Pseudocheirinae (Pseudochirulus + Pseudocheirus), Hemibelidinae (Hemibelideus + Petauroides), and Pseudochiropsinae (Pseudochirops + Petropseudes), respectively, and for an association of Pseudocheirinae and Hemibelidinae to the exclusion of Pseudochiropsinae. Within Pseudochiropsinae, Petropseudes grouped more closely with the New Guinean Pseudochirops spp. than with the Australian Pseudochirops archeri, rendering Pseudochirops paraphyletic. New Guinean species belonging to Pseudochirops are monophyletic, as are New Guinean species belonging to Pseudochirulus. Molecular dates and ancestral reconstructions of geographic provenance combine to suggest that the ancestors of extant New Guinean Pseudochirops spp. and Pseudochirulus spp. dispersed from Australia to New Guinea ∼12.1–6.5 Ma (Pseudochirops) and ∼6.0–2.4 Ma (Pseudochirulus). Ancestral state reconstructions support the hypothesis that occupation of high elevations (>3000 m) is a derived feature that evolved on the terminal branch leading to Pseudochirops cupreus, and either evolved in the ancestor of Pseudochirulus forbesi, Pseudochirulus mayeri, and Pseudochirulus caroli, with subsequent loss in P. caroli, or evolved independently in P. mayeri and P. forbesi. Divergence times within the New Guinean Pseudochirops clade are generally coincident with the uplift of the central cordillera and other highlands. Diversification within New Guinean Pseudochirulus occurred in the Plio-Pleistocene after the establishment of the Central Range and other highlands

Reappraisal of the Cormohipparion from the Valentine Formation, Nebraska. American Museum novitates ; no. 3163

56 p. : ill. ; 26 cm.Includes bibliographical references (p. 54-56