Adriana Oliver

Megacricetodon vandermeuleni, SP. Nov. (Rodentia, Mammalia), from the Spanish Miocene: a New Evolutionary Framework for Megacricetodon

ABSTRACT A new species of cricetid rodent, Megacricetodon vandermeuleni, sp. nov., is described from the local zone Db, middle Aragonian, from the Calatayud-Montalbán Basin and the Loranca Basin (Spain). The large-sized Megacricetodon is characterized by the elongated anteroconid and anterolophulid on ml and the robust and swollen cusps. Comparisons with other species of similar size and morphology are discussed. We consider M. bezianensis a valid species, based on the morphological differences with M. gersii. We propose a closely related group of Megacricetodon species that includes M. aff. collongensis, M. bavaricus, M. aff. bavaricus, M. bezianensis, M. lappi, M. aunayi, and M. vandermeuleni, nov. sp. The new species is of importance for Spanish biostratigraphy and the proposed Megacricetodon group is very useful for European faunal correlations and timing of migration events. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Stepwise onset of the Icehouse world and its impact on Oligo-Miocene Central Asian mammals

Central Asia is a key area to study the impact of Cenozoic climate cooling on continental ecosystems. One of the best places to search for rather continuous paleontological records is the Valley of Lakes in Mongolia with its outstandingly fossil-rich Oligocene and Miocene terrestrial sediments. Here, we investigate the response by mammal communities during the early stage of Earth’s icehouse climate in Central Asia. Based on statistical analyses of occurrence and abundance data of 18608 specimens representing 175 mammal species and geochemical (carbon isotopes) and geophysical (magnetic susceptibility) data we link shifts in diversities with major climatic variations. Our data document for the first time that the post-Eocene aridification of Central Asia happened in several steps, was interrupted by short episodes of increased precipitation, and was not a gradual process. We show that the timing of the major turnovers in Oligocene mammal communities is tightly linked with global climate events rather than slow tectonics processes. The most severe decline of up 48% of total diversity is related to aridification during the maximum of the Late Oligocene Warming at 25 Ma. Its magnitude was distinctly larger than the community turnover linked to the mid-Oligocene Glacial Maximum.

Oligocene and early Miocene mammal biostratigraphy of the Valley of Lakes in Mongolia

The Taatsiin Gol Basin in Mongolia is a key area for understanding the evolution and dispersal of Central Asian mammal faunas during the Oligocene and early Miocene. After two decades of intense fieldwork, the area is extraordinarily well sampled and taxonomically well studied, yielding a large dataset of 19,042 specimens from 60 samples. The specimens represent 176 species-level and 99 genus-level taxa comprising 135 small mammal species and 47 large mammals. A detailed lithostratigraphy and new magnetostratigraphic and radiometric datings provide an excellent frame for these biotic data. Therefore, we test and evaluate the informal biozonation scheme that has been traditionally used for biostratigraphic correlations within the basin. Based on the analysis of the huge dataset, a formalised biostratigraphic scheme is proposed. It comprises the Cricetops dormitor Taxon Range Zone (Rupelian), subdivided into the Allosminthus khandae Taxon Range Subzone and the Huangomys frequens Abundance Subzone, the Amphechinus taatsiingolensis Abundance Zone (early Chattian), the Amphechinus major Taxon Range Zone (late Chattian), subdivided into the Yindirtemys deflexus Abundance Subzone and the Upper Amphechinus major T. R. Z., and the Tachyoryctoides kokonorensis Taxon Range Zone (Aquitanian). In statistical analyses, samples attributed to these biozones form distinct clusters, indicating that each biozone was also characterised by a distinct faunal type.

Large-sized species of Ctenodactylidae from the Valley of Lakes (Mongolia): An update on dental morphology, biostratigraphy and paleobiogeography

Our study of the large and medium-sized species of Yindirtemys from the Valley of Lakes in Mongolia yielded three species: Yindirtemys deflexus, Y. suni and Y. birgeri. They differ in size and dental morphology. Yindirtemys suni is the largest and Y. birgeri the smallest species. Yindirtemys deflexus and Y. suni increase in body size but do not change dental morphology within their time range. The medium-sized Yindirtemys birgeri co-occurs in Mongolia with Y. deflexus in the late Oligocene (biozone C1) and is the easternmost occurrence of the species so far. Hitherto, Y. birgeri has been recorded from the Aral region in Kazakhstan only. Both Yindirtemys deflexus and Y. suni are used as biostratigraphic markers. Yindirtemys deflexus is a “key fossil” of the Chinese Land Mammal Age Tabenbulukian and for the Mongolian biozone C1; the latter correlates with the Oligocene. Yindirtemys suni is one of the “key fossils” of the Chinese Land Mammal Age Xiejian. In Mongolia the species ranges from the OligoceneMiocene transition (biozone C1-D) to the earliest Miocene (biozone D). The wide geographic range of Yindirtemys in the Oligocene of Asia suggests that no major physical barriers hampered mammal distribution between Kazakhstan, Mongolia and northern China, but local paleoecological and climatic conditions might have influenced mammal community structures in these areas. Adriana Oliver. Museo Nacional de Ciencias Naturales, MNCN-CSIC, C/ José Gutiérrez Abascal, 2, 28006, Madrid, Spain. Geological-Paleontological Department, Natural History Museum Vienna. Burgring 7, 1010 Vienna, Austria. adriana@mncn.csic.es Gudrun Daxner-Höck. Geological-Paleontological Department, Natural History Museum Vienna. Burgring 7, 1010 Vienna, Austria. gudrun.hoeck@nhm-wien.ac.at

Early Miocene Evolution of the Rodent Megacricetodon in Europe and Its Palaeobiogeographical Implications

The Megacricetodon material from Aliveri (Isle of Evia, Greece) was previously assigned to Megacricetodon primitivus, implying palaeobiogeographical relationship between south-eastern and south-western Europe. The material from Aliveri is here assigned to the new species Megacricetodon hellenicus sp. nov. This form has significant morphological differences compared to other Early Miocene species from Europe. This new evolutionary hypothesis of this genus has implications on the Early Miocene paleobiogeography of Europe. This work presents a new interpretation on the earliest European representative of the genus Megacricetodon from Aliveri localities. Analyses of the Megacricetodon material from MN 4 and MN 5 localities enable to propose a new palaeobiogeographical framework in which there are three main migration events of the genus Megacricetodon into Europe, each corresponding to different lineages that evolved independently. The new Greek taxon is considered the first migration wave from Anatolia, representing an endemic lineage different from any other European Megacricetodon.

New approaches to examining and interpreting patterns of dental morphological variability in Miocene cricetids

Morphometrical studies were carried out on the dental material of Democricetodon from the Calatayud-Montalbán Basin. Principal component analyses were incorporated into the analyses to reduce the number of metrical and morphological variables. Morphological variability was studied as the morphological distribution of character states, based on multivariate statistics, and plotted against time. The results of these analyses indicate that increased dental size is significantly correlated to the dental morphological value in the two Democricetodon lineages studied. We found that the rates of change in variables are not linear and that periods of higher rates can be correlated with global climatic changes. In addition, morphological variability is significantly correlated with relative abundances of the studied taxa. High morphological variability, as a proxy of niche breadth, may result from increased intraspecific interferences or from the relaxation of interspecific interactions caused by a decrease in primary productivity.

Diversification rates in Ctenodactylidae (Rodentia, Mammalia) from Mongolia

Gundis, or comb rats, are rodents of the family Ctenodactylidae. Extant gundis are restricted to Africa and represent a vestige of the diversity that the ctenodactylids attained at both palaeoecological and palaeobiogeographical levels. Here, we present an updated review of the Ctenodactylidae from the Valley of Lakes, Mongolia, based on the study of large collections now available. We have recognised 13 valid species of ctenodactylids grouped into five genera: Karakoromys, Huangomys, Tataromys, Yindirtemys, and Prodistylomys. The ctenodactylids show an initial burst in diversification in the early Oligocene followed by a sequential generic extinction of Karakoromys, Huangomys, and Tataromys. A maximum richness peak at the late Oligocene was followed by a profound diversity crisis. Yindirtemys, the only surviving genus, persisted into the Miocene, joining three Prodistylomys species. These last representatives of the group disappeared coinciding with the late Xiejian faunal reorganisation (Mongolian biozone D).

Wear reconstruction of the teeth of Yindirtemys deflexus (Ctenodactylidae, Rodentia) and evolution of its dental pattern

Abstract The dental pattern of Yindirtemys deflexus from Mongolia has been analysed using a Micro-CT scanner. This ctenodactylid exhibits a peculiar dental pattern, characterised by a mesodont dentition with some degree of selenodonty, an intricate enamel folding and elevated connections between cusps. Furthermore, the wear sequence in the upper tooth row shows very worn M1 even before other teeth emerge. The descriptive parameters used in the analyses (Area, Perimeter and structural density) allowed us to determine the relative wear stage in the different dental elements. The study reveals for Yindirtemys deflexus a wear pattern typical of mesodont teeth in which the maximum perimeter of the enamel is relatively constant over a large part of the crown height, and the Structural density decreases progressively until the senescence of the tooth. This peculiar dental morphology and eruption sequence of Y. deflexus is interpreted as the result of the evolution towards a relatively more durable dentition caused by the adaptation to more arid environments.

Neogene Mammal Sites in Molina de Aragón (Guadalajara, Spain): Correlation to Other Karstic Sites of the Iberian Chain, and their Geoheritage Values

Corral de Lobato, a karstic site in the area of Molina de Aragón has been studied in a preliminary way. Even though there are not many Neogene karstic sites in the Iberian Chain, they occur in four clusters, with ages ranging from latest middle Miocene (MN7/8) to early Pleistocene (MN17). Correlations between these clusters and the reference stratigraphical units of the Tagus Basin, as well as with local and global events, are proposed. These karstic sites provide a complementary source of fossil vertebrate remains to that of the stratified sites formed lowland. The Heritage significance of such sites arises from the enhanced preservation of rare taxa or associations, and the operation of biotic concentrative processes.

First faunal insights from biozone Db (middle Miocene, middle Aragonian) of the Madrid Basin (Spain)

AbstractPurposePalaeontological excavations following public works around the Manzanares River in the metropolitan area of Madrid yielded new small mammal fossil remains from two locations. We present here a description of their rodent assemblages, and a biostratigraphical and palaeoecological context of them. A comparison of these levels to the contemporaneous fossil localities of the Calatayud-Montalbán Basin and to other middle Aragonian sites from Madrid is also shown.MaterialA total of 371 dental elements have been studied from the five levels of the two locations (Puente de Praga site and Madrid Río2 site).ResultsThe rodent associations from the five new levels are similar and comprise eight taxa: Megacricetodon primitivus, Megacricetodon vandermeuleni, Democricetodon moralesi, Democricetodon sp., Armantomys aragonensis, Microdyromys koenigswaldi, Pseudodryomys ibericus and Heteroxerus rubricati. It represents a low equitable rodent community characterized by the predominance of the genus Megacricetodon and a poorly-represented fauna of glirids and sciurids.ConclusionsThe fossil association and its biostratigraphical markers indicate a correlation of the levels to the upper part of biozone Db, this being the first time that the rodent assemblages of this biozone are described in the Madrid Basin. Based on the rodent content we suggest more humid or/and more closed environments in biozone Db than in biozones Dc and Dd. The Calatayud-Montalbán record shows more diverse rodent assemblages in biozone Db, with taxa not recorded in Madrid that are indicative of more humid or structured environments. Therefore, the Madrid associations would represent dryer or/and more open environments than the Calatayud-Montalbán associations.