Paloma López-Guerrero

Revision of Cricetodon soriae (Rodentia, Mammalia), New Data from the Middle Aragonian (Middle Miocene) of the Calatayud-Daroca Basin (Zaragoza, Spain)

ABSTRACT The oldest record of Cricetodon (Cricetidae, Rodentia, Mammalia) from the Aragonian type area (Calatayud-Daroca Basin, Zaragoza, Spain) is described. The remains from Las Umbrías (LUM) and Las Planas (LP) sections are attributed to Cricetodon soriae, described in the locality Somosaguas N (SOMN) from the Madrid Basin (biozone E, MN5). The studied material (including 52 jugal teeth) belongs to eight localities spanning a time interval from 14.06 to 13.80 Ma, covering the entire biozone E. A morphometric analysis of the Calatayud-Daroca material provides the most specific and detailed descriptions of C. soriae until now. New complete descriptions of the type material from SOMN and an emended diagnosis of C. soriae are presented. Comparisons with all the species of Cricetodon described to date have been made. Differences between Cricetodon aureus and Cricetodon meini are discussed; the results yielded by the study of more than 100 upper third molars from Vieux-Collonges make it possible, for the first time, to distinguish between those of C. aureus and C. meini, and to compare them both with C. soriae. The presence of common characteristics indicates a closer relationship of C. soriae with the species of Cricetodon from Asia Minor than with the first representatives of Cricetodon in central and eastern Europe. The distribution of C. soriae in the Iberian Peninsula is coincident with the global cooling event and the increasing in aridity in southwestern Europe, and the faunal dispersion event called Conohyus/Pliopitechus that took place during the local biozone E.

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.

New insights on Cricetodontini (Rodentia, Mammalia) from the Duero Basin, Spain

Abstract The tribe Cricetodontini is a common cricetid group found in several European basins from the Miocene. Here we present a study of the fossils of this group found in the Duero Basin. We updated the biostratigraphical assignation of some of the localities in which several species of Cricetodontini have been found. Cricetodontini remains from eight localities from the central sector of the Duero Basin have been described, measured and assigned to a species. The presence in these localities of Hispanomys aguirrei, H. lavocati, H. nombrevillae and H. aragonensis has allowed correlating them to the biostratigraphic scale built for the Miocene in Calatayud-Daroca Basin, identifying biozones G3, H and I (MN7/8 – MN10, Late Aragonian – Early Vallesian, Middle – Late Miocene). Furthermore, this study constitutes the first citation of this species in this basin, except H. aguirrei, previously described in the Duero Basin. After this work, the biostratigraphical assignation of the studied sites is now well known. We evidenced the resemblance of Duero and Calatayud-Daroca basins.

The record of Aplodontidae (Rodentia, Mammalia) in the Oligocene and Miocene of the Valley of Lakes (Central Mongolia) with some comments on the morphologic variability

The present publication reports new discoveries of Oligocene and early Miocene aplodontid rodents from the Taatsiin Gol area (Valley of Lakes) in Mongolia. The fossil aplodontids recovered in this area are mainly composed of dental remains, some fragmentary jaws plus one partially preserved skull. Aplodontid rodents have been found from the early Oligocene (local biozone A) to the early middle Miocene (local biozone D). Altogether, eight taxa belonging to five genera have been identified in the investigated deposits: Ninamys arboraptus, Ninamys kazimierzi, Promeniscomys cf. sinensis, Prosciurus? mongoliensis and Prosciurus? sp. nov. in the early Oligocene; N. arboraptus, Proansomys badamae sp. nov. and Ansomyinae indet. in the late Oligocene; and Ansomys sp.1 in the early Miocene. In addition, although outside of the topic of the present special issue, one additional taxon, Ansomys sp.2, is reported from the ?middle Miocene. The material of aplodontids is usually relatively scarce in Asian localities. For the first time, with a sample size of 81 specimens, the material from Central Mongolia (mainly from the Oligocene) now allows a more accurate description of the morphological and size variability and resolves some systematic problems. The study of these aplodontids reveals that they are more abundant and diverse in the early Oligocene and that the diversity decreases during the late Oligocene and Miocene. One hypothesis, to explain the opposite diversity trend observed previously for sciurids in the same region, is that both Sciuromorpha families might have competed for the same resources from the early Oligocene to the middle Miocene in Central Mongolia.

A new species of Argyromys (Rodentia, Mammalia) from the Oligocene of the Valley of Lakes (Mongolia): Its importance for palaeobiogeographical homogeneity across Mongolia, China and Kazakhstan

We describe a new species of Rodentia (Mammalia), Argyromys cicigei sp. nov. from Toglorhoi (fossil bed TGW-A/2a) in Mongolia and Ulantatal (fossil beds UTL 1 and UTL 7) in China. Its tooth morphology differs from the type species Argyromys aralensis from Akespe in Kazakhstan by smaller size and simpler structures. Argyromys has been assigned in different families of Muroidea, such as Tachyoryctoididae and Spalacidae. However, the presence of common characters indicates a closer relationship of Argyromys with the genera of Cricetidae s.l. (subfamilies Eucricetodontinae; Cricetopinae; Cricetodontinae and Gobicricetodontinae among others) from Asia than with the earliest representatives of Spalacidae or the endemic Tachyoryctoididae. Argyromys cicigei sp. nov. possesses a simple anterocone and anteroconid in the upper and lower first molars, respectively, which is characteristic for Cricetidae s.l. It has a flat occlusal surface in worn specimens; weakly-developed posterolophs; an oblique protolophule and metaloph on the upper molars and it lacks a labial anterolophid on the m1. These traits are also typical of the Oligocene genera Aralocricetodon and Plesiodipus, included in the subfamilies Cricetodontinae and Gobicricetodontinae respectively. The cladistic analysis performed here supports this hypothesis. The clade formed by Argyromys species is grouped with other cricetid taxa (s.l). Spalacids, however, form a different clade, as do the tachyoryctoids. Previous authors state that the Aral Formation (Kazakhstan) should be dated to the Oligocene instead of the Miocene, based on the presence of several taxa. The finds of Argyromys in both regions supports the statement that they are closer in age than previously thought. The occurrence of Argyromys in Kazakhstan, Mongolia and China evidences the biogeographic unity of the Central Asian bioprovince during the Oligocene.

Fourier analysis applied to Cricetodon and Hispanomys (Rodentia, Mammalia): its use as a taxonomical criterion

ABSTRACT Cricetodon and Hispanomys are two extinct rodent genera belonging to the same tribe. Cricetodon presents generally a more primitive morphology than Hispanomys. However, they share some traits and some species present a combination of primitive and derived characters (called mosaic morphological pattern) that difficult assessing the evolutionary stage of the species or their attribution into a genus. Fourier Shape Analysis, a geometric morphometrics method, is used to quantify the outline form of the upper first molar of these genera and to differentiate them. New mathematical criterion is obtained to analyse the morphology of this particular species with mosaic morphology. First, the validity of the method is tested with one basal (C. meini) and one derived species (H. aragonensis). Two different outlines are statistically distinguished: straight in Cricetodon and trilobed in Hispanomys. This result allowed us to undertake the study of some other species included in both genera. This complete analysis enabled us to describe the outline of ‘Cricetodon’ klariankae and ‘Cricetodon’ fandli. Both share the same morphospace than the rest of the species of Hispanomys. This could indicate that both species could be included in Hispanomys.