Early Miocene evolution of the rodent Megacricetodon in Europe and its palaeobiogeographical implications

Received 20 June 2014, accepted 15 September 2014, available online 23 October 2014The Megacricetodon material from Aliveri (Isle of Evia, Greece) was previously assigned to M. 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.This research was supported by the Spanish MINECO Project No. GL-2008-04200/BTE and CGL2011-28877Peer reviewe

Preliminary study of rodents from the Golliher B assemblage of Meade County, Kansas, USA indicates an intense cold period near the end of the Pleistocene

Submission: 15 June 2007. Acceptance: 18 May 2011An assemblage of rodents recovered from a thin layer of sediments along Sand Creek on the Golliher Ranch in Meade County, Kansas, indicates that cold steppe conditions likely prevailed for a brief time near the close of the Pleistocene around 12,500 radiocarbon years ago. This environment is suggested by the northern disjunct rodents Zapus princeps, Microtus pennsylvanicus, Thomomys cf. talpoides and the presumed cold steppe vole Microtus (Pedomys) parmaleei, n. sp., plus the absence of cotton rats. Comparison of meadow vole m1 crown morphology diversity through the late Pleistocene in Kansas shows that the modern pattern of diversity developed in a brief period of 1500 years, possibly during the Younger Dryas interval. A cement-filled prism fold, a feature commonly encountered in extinct species of Mimomys with rooted molars, appears in three rootless first lower molars of Microtus pennsylvanicus. The Golliher B assemblage helps to fill in the late Pleistocene history of rodents in the ongoing Meade Basin Rodent Project.Peer reviewe

New Species of Rotundomys (Cricetinae) from the Late Miocene of Spain and Its Bearing on the Phylogeny of Cricetulodon and Rotundomys

The material of Rotundomys (Rodentia, Cricetinae) from the Late Miocene fossiliferous complex of Cerro de los Batallones (Madrid, Spain) is described and compared with all species currently placed in the genera Rotundomys and Cricetulodon. Both the morphology and size variation encompassed in the collection of specimens from Batallones suggest they belong to a single taxon different from the other known species of these genera. A new species Rotundomys intimus sp. nov. is, therefore, named for it. A cladistic analysis, which is the first ever published concernig these taxa, has been conducted to clear up the phylogenetic position of the new species. Our results suggest that Rotundomys intimus sp. nov. inserts between R. mundi and R. sabatieri as a relatively primitive taxon inside the clade Rotundomys. The new taxon is more derived than R. mundi in having a transversal connection between the metalophulid and the anterolophulid on some m1 but more primitive than R. sabatieri and the most evolved species of Rotundomys (R. montisrotuni +R.bressanus) in its less developed lophodonty showing distinct cusps, shallower valleys, and the presence of a subdivided anteroloph on the M1. The species of Cricetulodon do not form a monophyletic group. As a member of Rotundomys, Rotundomys intimus sp. nov. is more derived than all of these taxa in its greater lophodonty and the complete loss of the anterior protolophule, mesolophs, and mesolophid.Ministerio de Economía y Competitividad (MINECO)Universidad Complutense de MadridDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Local accumulation of diacylglycerol alters membrane properties nonlinearly due to its transbilayer activity

Diacylglycerols (DAGs) are bioactive lipids that are ubiquitously present at low concentrations in cellular membranes. Upon the activation of lipid remodeling enzymes such as phospholipase C and phosphatidic acid phosphatase, DAG concentration increases, leading to a disruption of the lamellar phase of lipid membranes. To investigate the structural origin of these phenomena, here we develop a coarse-grained model for DAGs that is able to correctly reproduce its physicochemical properties, including interfacial tension and flip-flop rate. We find that even at low concentrations a nonnegligible percentage of DAG molecules occupies the interleaflet space. At high concentrations, DAG molecules undergo a phase- separation process from lamellar lipids, segregating in DAG-only blisters and effectively reducing the DAG surface pool available to peripheral enzymes. Our results allow for a better understanding of the role of DAGs in cellular membranes and provide a new tool for the quantitative estimation of low-abundance lipids on membrane properties

Primeras faunas de micromamíferos del Paleógeno de La Cuenca del Duero

Se estudian cinco yacimientos de micromamiferos del Eoceno de la Cuenca del Duero, región de Zamora y Salamanca (Jambrina, Santa Clara, Babilafuente y Sanzoles) y de la región de Almazán (Miñana). Las faunas de micromamíferos aparecidas en ellos nos han permitido situar sus asociaciones en la escala cronológica del Paleógeno europeo (SCHMIDT-KITTLER, 1987) y datar asi con relativa precisión los tramos en los que se encuentran. Los yacimientos de Zamora corresponderfan al Neustriense -Rhenaniense, siendo el de Santa Clara Rhenaniense Medio (Eoceno Medio). El de Salamanca correspondería al Rhenaniense Superior (Eoceno Medio final) y el de Almazán al Eoceno Superior. La similitud de algunos elementos faunísticos hallados en Zamora con faunas asiáticas. [ABSTRACT] Five gisements of Eocene micromammals of Duero Basin in the Zamora (Jambrina, Santa Clara, Babilafuente and Sanzoles) and Almazán (Miñana) areas are studied. The associations of micromammals found can be placed in the Chronologic scale for the European Paleogene (as stablished by SCHMIDT-KITTLER, 1987) and, as a consequence, the deposits they occur in have been dated with certain accuracy. The deduced ages are: Zamora: Neusttian-Rhenanian; Santa Clara: Middle Rhenanian (Middle Eocene); Salamanca: Upper Rhenanian (Uppemrost Middle Eocene) and Almazán: Upper Eocene. The similitude of some faunistic elements found in Zamora with asiatic faunas are thought to be of biogeographical importance as far as the relationships between Europe and Asia during the Eocene times are concerned

Los Mamíferos del Paleoceno superior de la Formación Tremp: implicaciones en la correlación marino-continental

Four micromammal localities from the upper Tremp Formation (Upper Paleocene, Lleida, Spain), closely below the llerdian stratotype, have delivered near 250 teeth from ten condylartha, insectívora, proteutheria and multituberculate species. The low diversity of these assemblages, together with the neighbour Campo (Huesca), and their intermediate biochronological situation between Cernaysian and Neustrian European mammal ages allow to define a new MP6b unit, situated in the Cernaysian age and correlated with lower Clarkforkian (Cf 1-2) north-American mammal unit, thus filling a gap in the European continental biochronology. They can be calibrated within NP9 nannoplancton biozone and between SBZ 3 (Clomalveolina primaeva) - SBZ 5 (Alveolina vredenburgi) shallow benthic zones and chrons C25n-C24r. The diversity curves fit in both continents: the MP6b-Cf 1-2 epochs represent a period of very low mammalian diversity, followed by increasingly diversified Neustrian European mammalian assemblages, here divided into MP7a and MP7b units. This epoch correlates well with the Clarkforkian-Wasatchian transition in North America (Cf 3-W 0-4), which correspond with the Late Paleocene Therma Maximum. According to the mammalian biochronology, the dCI3 anomalies detected in relation with European mammal sites must correspond to two successive episodes, one below the Palette MP7a site, and another above the Dormaal MP7b site. In any case, the mammalian migratory wave in both continents is not rapid and synchronous but gradual and diachronous

Hipparion dispersal in Europe: magnetostratigraphic constraints from the Daroca area (Spain)

The Nombrevilla section in the Calatayud-Daroca basin (Central Spain) bears one of the best late Aragonian to early Vallesian large and small vertebrate fossil records in Europe, including important findings of the equid Hipparion. Magnetostratigraphic dating of the Nombrevilla section thus provides further age constraints on the timing of Hipparion dispersal in Europe, a bioevent which defines the base of the Vallesian mammal stage. Correlation of the Nombrevilla magnetic polarity stratigraphy to the geomagnetic polarity time scale is supported by the identification of the characteristic long normal chron C5n in the upper half of the section,... (Ver más) in association with early Vallesian (early late Miocene) fossils. The classic mammal fossil site Nombrevilla 1, recording the earliest occurrence of Hipparion, correlates to the lower third of chron C5n, and yields an interpolated age of about 10.7-10.8 Ma. This age is in agreement with magnetostratigraphic dating of earliest occurrences in Siwaliks of Pakistan and some 40Ar/39Ar ages of Mediterranean sites. The youngest pre-Hipparion large mammal fossil record corresponds to Nombrevilla 9, a site wich approximately correlates to chron C5r.1n, at about 11.1 Ma. This result is nearly in conflict with the data from the Vallès-Penedès, where a Hipparion bearing site is correlated to the same chron. In addition, Nombrevilla 9 yields a small mammal assemblage which corresponds to local zone H, a biozone wich was classically correlated to the lower Vallesian. This implies a diachrony of about 300 kyr between the lower boundary of zone H and the first occurrence of Hipparion (base of the Vallesian) in the Calatayud-Daroca basin. Correlation of the Aragonian levels of Nombrevilla 2, 3 and 4 is not yet certain and would require further downward extension of the magnetostratigraphy in a neighbouring section. Nevertheless, we can confidently say these localities are younger than 11.6 Ma

The Molecular Mechanism of the Catalase-like Activity in Horseradish Peroxidase

Horseradish peroxidase (HRP) is one of the most relevant peroxidase enzymes, used extensively in immunochemistry and biocatalysis applications. Unlike the closely related catalase enzymes, it exhibits a low activity to disproportionate hydrogen peroxide (H2O2). The origin of this disparity remains unknown due to the lack of atomistic information on the catalase-like reaction in HRP. Using QM(DFT)/MM metadynamics simulations, we uncover the mechanism for reduction of the HRP Compound I intermediate by H2O2 at atomic detail. The reaction begins with a hydrogen atom transfer, forming a peroxyl radical and a Compound II-like species. Reorientation of the peroxyl radical in the active site, concomitant with the transfer of the second hydrogen atom, is the rate-limiting step, with a computed free energy barrier (18.7 kcal/mol, similar to 6 kcal/mol higher than the one obtained for catalase) in good agreement with experiments. Our simulations reveal the crucial role played by the distal pocket residues in accommodating H2O2, enabling formation of a Compound II-like intermediate, similar to catalases. However, out of the two pathways for Compound II reduction found in catalases, only one is operative in HRP. Moreover, the hydrogen bond network in the distal side of HRP compensates less efficiently than in catalases for the energetic cost required to reorient the peroxyl radical at the rate-determining step. The distal Arg and a water molecule in the "wet" active site of HRP have a substantial impact on the reaction barrier, compared to the "dry" active site in catalase. Therefore, the lower catalase-like efficiency of heme peroxidases compared to catalases can be directly attributed to the different distal pocket architecture, providing hints to engineer peroxidases with a higher rate of H2O2 disproportionation