Biochronological Scale Research Articles

Zonal biochronological method for solving long-living problems of general stratigraphy

Research subject. Problematic issues of general stratigraphy are considered, including the Karpinsky principle, the unification of autonomous zonal biochronological scales (BCS), the basics of stratigraphic classification, the relation of zonal biostratigraphic and chronostratigraphic units. Materials and methods. The existing standard solutions to the above issues are analyzed. An attempt is made to reveal the logical sources of contradictions and to pave ways for a consistent synthesis. Results. The necessity for a successful solution of these issues to abandon the identification of the biochronological scale and the geological section is shown. From the recognition of the zone as the smallest subdivision of the biochronological scale, the linearity of the zonal subdivisions of the scale follows, which makes it a correct tool for performing basic stratigraphic operations – section subdivision and correlation of the boundaries of stratigraphic units. Strict differentiation of the scale from a section studied using this scale makes it possible to fulfill all the requirements of the Karpinsky principle regarding dividing horizons with mixed fauna. The same condition underlies the creation of a stratigraphic classification, which must be preceded by a clear separation of the material (“mapped”) stratigraphic units of the Earth’s crust and units of chronological scales, which are used for their correlation. Placing them in a single “dualistic” stratigraphic classification cannot give a satisfactory result. The creation of autonomous zonal scales should be preceded by the definition of the biozones of the species used to build these scales, according to the normative (standard) zonal scale for a given stratigraphic interval. Taking into account the minimum dimension of the zonal subdivisions of the standard scale, the zones of autonomous scales distinguished by this method correspond to a whole number of normative zones, and, therefore, the boundaries of the stratozones established on the autonomous scales, in this case, will certainly coincide with any boundaries of the stratozones, distinguished on the normative scale. This procedure makes it possible to perform the unification of autonomous zonal BCSs based on different groups of fossils. Zonal BCS performs correlation functions, zonal units are a tool for chronological identification of remote geological objects, including the boundaries of chronostratigraphic units, although not being included in their hierarchy. Conclusions. A biochronological scale is a model of the biochronological calculation of geological time and cannot be identical to what it models. Differentiation of the scale from a section studied using this scale is an indispensable condition that precedes and ensures the successful solution of long-living problems of general stratigraphy.

Boreal Toarcian Biochronological Zonation by Bivalves of the Genus <i>Meleagrinella</i> Whitfield, 1885

Based on the chronological sequence of species of the bivalve genus Meleagrinella Whitfield, 1885 (family Oxytomidae Ichikawa, 1958) established in the Toarcian deposits of Northeast Russia, Eastern Siberia, and South Germany, a biochronological scale of the Lower Toarcian is proposed. Three oxytozones corresponding to Boreal ammonite zones are established: Meleagrinella golberti Oxytozone = Tiltoniceras antiquum and Harpoceras falciferum zones; Meleagrinella substriata Oxytozone = Dactylioceras commune Zone; Meleagrinella prima Oxytozone = Zugodactylites braunianus and Pseudolioceras compactile zones. Using the proposed zonation, an interregional correlation of sections of the Lower Toarcian of the North-East of Russia (Astronomicheskaya, Saturn, Brodnaya, Start rivers), Eastern Siberia (Anabar Bay, Markha, Tyung, Vilyui, Kelimyar, Motorchuna, wells of the Vilyui syneclise) and South Germany (the Ludwig Canal) is performed.

Biochronological scheme of the Quaternary of the south of Eastern Europe and its substantiation based on arvicoline teeth morphometrics

The construction of regional biochronological scales for the Pleistocene based on remains of small mammals is a systematic and successive process of accumulation of informative data with their subsequent presentation in the form of schemes and tables. The geological and palaeontological characteristics of reference sections are presented in detail. Faunal assemblages and developmental phases in associations of small mammals in the south of Eastern Europe are described based on the taxonomic composition of Pleistocene micromammal fauna. Ortho- and parastratigraphic taxa are identified and phylogenetic trees are constructed based on modifications of morphological traits in the evolution of separate species. A macroevolutionary biochronological scale has been compiled using several types of biochronozones. A phenozone-based microevolutionary biochronological scale has been established for the Quaternary of the south of Eastern Europe. These scales can be used to subdivide Quaternary deposits of this region by identifying biostratigraphic units and correlating them on local and regional scales.

New Biochronological Scales of Planktic Foraminifera for the Early Danian Based on High-Resolution Biostratigraphy

After the Cretaceous/Paleogene boundary (KPB) catastrophic mass extinction event, an explosive evolutionary radiation of planktic foraminifera took place in consequence of the prompt occupation of empty niches. The rapid evolution of new species makes it possible to establish high-resolution biozonations in the lower Danian. We propose two biostratigraphic scales for low-to-middle latitudes spanning the first two million years of the Danian. The first is based on qualitative data and includes four biozones: the Guembelitria cretacea Zone (Dan1), the Parvularugoglobigerina longiapertura Zone (Dan2), the Parvularugoglobigerina eugubina Zone (Dan3), and the Parasubbotina pseudobulloides Zone (Dan4). The latter two are divided into several sub-biozones: the Parvularugoglobigerina sabina Subzone (Dan3a) and the Eoglobigerina simplicissima Subzone (Dan3b) for the Pv. eugubina Zone, and the Praemurica taurica Subzone (Dan4a), the Subbotina triloculinoides Subzone (Dan4b), and the Globanomalina compressa Subzone (Dan4c) for the P. pseudobulloides Zone. The second scale is based on quantitative data and includes three acme-zones (abundance zones): the Guembelitria Acme-zone (DanAZ1), the Parvularugoglobigerina-Palaeoglobigerina Acme-zone (DanAZ2), and the Woodringina-Chiloguembelina Acme-zone (DanAZ3). Both biozonations are based on high-resolution samplings of the most continuous sections of the lower Danian worldwide and have been calibrated with recent magnetochronological and astrochronological dating.

Biochronological Scale of the Upper Toarcian–Lower Aalenian of Eastern Siberia by Bivalve Mollusks of the Genus Arctotis Bodylevsky, 1960

Biochronological Scale of the Upper Toarcian–Lower Aalenian of Eastern Siberia by Bivalve Mollusks of the Genus Arctotis Bodylevsky, 1960

Stratigraphic scale and geological section

Research subject. The most frequently utilized fundamental notions in stratigraphy are discussed: concrete section, composite section, the stratigraphic scale, the biochronologic scale, the International Stratigraphic Scale. Materials and methods . The conventional content of these concepts is analyzed. The logical invalidity and negative consequences of the identification of subdivisions of the stratigraphic scale and subdivisions of a section are shown. The study of a section provides a way of obtaining information about the stratigraphic sequence of rock formation and the distribution of evidence of the events included in them, which are necessary for constructing stratigraphic scales. The close connection of the source of the actual data and results of its stratigraphic interpretation is the reason for the traditional identification of the subdivisions of the stratigraphic scale and subdivisions of a particular section. Results. The biochronologic scale inherits from a section the time sequence of occurrences of species of a certain group of organisms selected as the basis of a scale. However, special features of the evolutionary development of organisms do not depend on the composition of the containing deposits and the method of the separation of sedimentary rock sequences. This development makes it possible during the study of many specific sections to establish homotaxis in the distribution of fossils, i.e., to build a biochronologic scale. Thus, the understanding of the scale is a model of the biochronologic calculation of geological time. Like any model, a scale cannot be identical to what it simulates. Conclusion. A precise differentiation of the scale and a section is the basis for drawing correct stratigraphic conclusions. A zone is the smallest subdivision of the biostratigraphic scale. Zones are not divided into parts, are discrete (between adjacent zones there are no time passages), equivalent and are characterized by only the place which it occupies on the scale. The construction of a zone scale precedes the establishment of the material equivalent of the zone - of a stratozone - in the section. Any part of a stratozone is dated by the complete zone. The identification of the zonal scale with a sequence of stratozones in the section does not make it possible to understand the minimum dimensionality of a zone subdivision. The International Stratigraphic Scale (ISS) is defined, based on domestic stratigraphic codes and on foreign reference books, as a stratigraphic sequence of rocks (geological bodies) in total volume without passages and overlaps. In this treatment the ISS is not the scale, but is a complete (composite) geological section of the earth’s crust. The biostratigraphic scale serves as a tool of correlation. The ISS gives only the name of that subdivision, with which a concrete section is compared, and the geological age of the deposits of this section is designated by this name.

Mammal Biochronology (Land Mammal Ages) Around the World From Late Miocene to Middle Pleistocene and Major Events in Horse Evolutionary History

Biochronology is important to vertebrate chronology because the primary temporal units developed and applied by vertebrate paleontologists for correlation of terrestrial deposits (Land Mammal Ages, LMA) are all biochronologic units. Specific mammal biochronologic scales have been developed for Europe (MN units or ELMA), Asia (ALMA), North America (NALMA) and South America (SALMA). Each timescale is based on land mammal first appearances and characteristic associations on different continental landmasses. Herein, we summarize and review the bases for recognizing mammalian biochronologic units with the most recent update of the Land Mammal Ages. We correlate these ages with the global magnetochronostratigraphic and geochronologic time scales including the major equid evolutionary events of the last 8 million years.

The Palaeotheriidae (Equoidea, Perissodactyla, Mammalia) from the Eocene fauna of Aumelas (Hérault department, France)

The rich vertebrate fauna of Aumelas has from decades been the subject of several partial publications, which led to assign it an age close to the MP 13 reference level in the biochronological scale of Western European mammals; but it is still partially unpublished and this paper is part of a general review of the fauna. With regard to equoid perissodactyls, five taxa have been distinguished, to be assigned to the “Pachynolophinae” to the exclusion of any Palaeotheriinae. Two leading species appear in this ensemble: Propalaeotherium sudreiRemy, Krasovec & Marandat, 2016 and Pachynolophus ruscassierensis n. sp. The three other taxa are less documented, which prevents a specific determination, Pachynolophus sp., Propalaeotherium cf. gaudryi (Lemoine, 1878) and Lophiotherium sp. All of these species display relatively archaic features as highlighted by a cladistic analysis. Such a conclusion challenges the hitherto prevailing consensus on the dating of the fauna, in the sense of an older biochronological age. This discrepancy will be discussed in a subsequent synthetic work, in conjunction with specialists of all mammal and reptile orders represented in the locality.

The oldest Cenozoic mammal fauna of Europe: implication of the Hainin reference fauna for mammalian evolution and dispersals during the Paleocene

The mammal fauna of Hainin is particularly interesting as the oldest in the Cenozoic of Europe, and the earliest reference level (MP1–5) of the mammalian biochronological scale for the European Palaeogene. This paper summarizes the mammal taxa discovered in the fauna, presents an analysis of the fauna as a whole (relative abundance and species richness), and describes four new eutherians: Belgoryctes thaleri gen. et sp. nov., Eurolestes dupuisi gen. et sp. nov., Quadratodon sigei gen. et sp. nov. and Cingulodon magioncaldai gen. et sp. nov. The assemblage is relatively small (about 400 dental specimens), characterized by a high diversity and abundance of small insectivorous species and very low abundance of ‘plesiadapiforms’ and ‘condylarths’. By comparison with younger European Paleocene faunas, ‘condylarths’ and ‘plesiadapiforms’ became more and more abundant and diverse through the Paleocene but collapsed at the Paleocene–Eocene Boundary. ‘Proteutherians’ declined steadily, while multituberculates remained diverse, although the early Paleocene was populated mainly by Kogaionidae whereas the late Paleocene was dominated by Neoplagiaulacidae. The palaeoecology of Hainin is deduced from the mammal assemblage: the local environment was likely a forested area. Stratigraphically, the Hainin deposits are most likely of late Danian age, and biochronologically its fauna represents a partial equivalent of the North American Torrejonian Land Mammal Age. When compared to younger Paleocene faunas of Europe, the composition of the Hainin fauna reveals that a relatively important intercontinental dispersal of mammals occurred around the Danian–Selandian boundary, roughly corresponding to the Torrejonian–Tiffanian boundary. This dispersal is marked by the arrival in Europe of typically North American taxa such as arctocyonids, plesiadapids and neoplagiaulacid multituberculates. Additional exchanges of lesser magnitude probably also occurred around the Selandian–Thanetian boundary (i.e. during the Tiffanian), although the evidence is less compelling and mainly concerns the plesiadapids Chiromyoides and Plesiadapis.http://zoobank.org/urn:lsid:zoobank.org:pub:A240BAE2-7446-4DBD-A597-7BEFE58447DF

Micropalaeontological dating of the Prémontré mammal fauna (MP10, Prémontré Sands, EECO, early late Ypresian, Paris Basin)

1. IntroductionAs a result of long-term and intensive fossil collecting (see Russell, 1964; Rat, 1965 and Louis, 1996 for overviews) the Paris Basin has become one of the hot spots in the reconstruction of Paleogene continental mammal evolution, and the home of about two thirds of the reference levels of the European Paleogene mammalian biochronological scale (Schmidt-Kittler, 1987). This particular status is also due to its position along the eastern edge of the Atlantic Ocean, allowing marine and continental strata to meet, and its particular tectonic history. Large parts of the Paris Basin were affected by strong subsidence generating relatively complete and rather thick sedimentary successions, marine as well as continental (Gely & Lorenz, 1991; Duprat, 1997a). In spring 1980, an almost 20 m thick succession of essentially sandy sediments has been exposed during works inside the Psychiatric Hospital of Premontre. This hospital was built on the ruins of the medieval Premontre Abbey, about 15 km west of the city of Laon, in the northeast of the Paris Basin (Fig. 1). Since its discovery scientists have been mainly focussing on the lower part of the Premontre section (unit 2 of Degremont et al., 1985, for which these authors introduced the term Premontre Sands), which yielded an intriguing mix of continental, terrestrial as well as aquatic, and marine fossils. A preliminary list of these taxa was given by Degremont et al. (1985), mentioning plant fragments (seeds, wood, leaf

Carbon and strontium isotope stratigraphy of the Upper Cretaceous (Cenomanian-Campanian) shallow-water carbonates of southern Italy: Chronostratigraphic calibration of larger foraminifera biostratigraphy

Shallow-water carbonates are invaluable archives of past global change. They hold the record of how neritic biologic communities reacted to palaeoenvironmental changes. However, attempts to decipher these geological archives are often severely hampered by the low stratigraphic resolution attained by biostratigraphy. This is particularly the case for the Upper Cretaceous carbonate platforms of the central Tethyan realm: their biostratigraphy suffers from very low resolution and poor correlation with the standard biochronologic scales based on ammonites, planktic foraminifers and calcareous nannoplankton.In this paper we show how this problem can be tackled by integrating biostratigraphy with isotope stratigraphy. We present a detailed record of the benthic foraminiferal biostratigraphy and carbon and strontium isotope stratigraphy of three upper Cenomanian-middle Campanian sections belonging to the Apennine Carbonate Platform of southern Italy. For the upper Cenomanian-Turonian interval, the carbon isotope curves of the studied sections are easily correlated to the reference curve of the English Chalk. The correlation is facilitated by the matching of the prominent positive excursion corresponding to the Oceanic Anoxic Event 2. For the Coniacian-middle Campanian interval, the correlation is mainly based on strontium isotope stratigraphy. We use the 87Sr/86Sr ratios of the low-Mg calcite of well preserved rudist shells to obtain accurate chronostratigraphic ages for many levels of the three studied sections. The ages obtained by Sr isotope stratigraphy are then used to better constrain the matching of the carbon isotope curves.From the high-resolution chronostratigraphic age-model stablished by isotope stratigraphy, we derive the chronostratigraphic calibration of benthic foraminiferal biostratigraphic events. For the first time the benthic foraminiferal biozones of the Apennine Carbonate Platform can be accurately correlated to the standard ammonite biozonation. This result is of great relevance because the biostratigraphic schemes of other carbonate platforms in the central and southern Tethyan realm are largely based on the same biostratigraphic events.

An unexpected record of the PETM in terrestrial and organic sediments of Avesnois, between the Paris and Belgian Basins, NW Europe

An unexpected record of the PETM in terrestrial and organic sediments of Avesnois, between the Paris and Belgian Basins, NW Europe

The Upper Ypresian and Lutetian in San Pelegrín section (Southwestern Pyrenean Basin): Magnetostratigraphy and larger foraminifera correlation

The current available Shallow Benthic Zones (SBZs) calibration based on larger foraminifera is now being improved for the Paleogene Period. In this work, the San Pelegrín section in the External Sierras, shows new magnetostratigraphic and biostratigraphic information from the Southwestern Pyrenean basin, where the larger thickness of the shallow marine platforms were developed. This environment represents the appropriate frame to calibrate the SBZ scale. Moreover the magnetostratigraphic data can be correlated with biostratigraphic data obtained directly at the same section, avoiding limitations of previous correlations. The San Pelegrín section presents 530m of Ypresian and Lutetian rocks; 169 sampled levels for magnetostratigraphic purposes have been studied, a fact that guarantees the independence and resolution of this record. Thermal and alternating field demagnetizations were carried out to unravel the characteristic remanent magnetization, and the orthogonal diagrams show stable normal and reverse polarity directions. Three pairs of magnetozones were found along the section enabling to define a robust and reliable local polarity sequence correlated with chrons C23, C22, C21n and C20r. The biostratigraphic study distinguished three Shallow Benthic Zones from SBZ11 to SBZ13. The combination of magneto and biochronologic scales is very useful to improve and to accurate the available shallow benthic zone calibration for this time gap, especially for the SBZ11 zone. Now the base of SBZ11 can be located, at least, in 50.96My, because the association is still present at the top of C23n. This data is older than previously thought from existent scales. On the other side, the SBZ11 top falls within chron C22n. The occurrence of a sedimentary hiatus between C22n and C21n prevents an accurate calibration of the SBZ12 top, but our profile proves the relation of SBZ12 with C22n as well. Finally the SBZ13 zone falls within the limits of recent recalibrations (C21n to C20r).

A new occurence of the genus Tonkinella in northern Spain and the Middle Cambrian intercontinental correlation

The genus Tonkinella is a typical polimeroid trilobite in lower Middle Cambrian rocks from Vietnam, Canada, U.S.A., India, Korea, Siberia, China and Argentina. It has recently been found in the Mediterranean region (Iberian Chain, northeastern Spain). In this paper we refer the finding of Tonkinella aff. breviceps in the Leonian (lower Middle Cambrian) of the Cantabrian Mountains (northern Spain), analysing its stratigraphical position, fossil assemblages, biochronology and utility for intercontinental correlation. The presence of this taxon allows us to make a more accurate correlation between the Middle Cambrian biochronological scales of Laurentia, the Mediterranean area and China.

Pleistocene debris-flow deposition of the hippopotamus-bearing Collecurti bonebed (Macerata, Central Italy): Taphonomic and paleoenvironmental analysis

An integrated taphonomic-sedimentological study provides insight into the origin, preservation biases and paleobiological significance of the latest Early/earliest Middle Pleistocene bonebed of Collecurti, near Colfiorito (Macerata, central Italy), which represents an important benchmark in the European biochronological scale. Sedimentological evidence indicates that the bonebed is hosted in a debris-flow deposit which was emplaced in a shallow lacustrine setting. Geologic and geomorphic controls on sedimentation in the intermontane Colfiorito Basin provided an ideal setting for the development of cohesive mass flows, due to high-relief and poorly integrated catchments along the basin margin, and the abundance of detrital fines yielded by Mesozoic sedimentary rocks of the local basement. The fossil assemblage includes 496 bones, with a minimum of 24 individuals representing 9 species and 8 genera, dominated by Hippopotamus antiquus. The hippopotamus remains include partially articulated carcass parts as well as closely associated elements. Few disarticulated elements, which are bones that can be more easily transported hydraulically, were involved in pre-debris-flow winnowing and sorting, and then entrained by the debris flows in nearby uplands, transported a short distance down into a shallow pond or lake margin, where the flow buried hippopotamus carcasses that had accumulated in the pond/lake. The hippopotamus carcasses were in an advanced state of decomposition when the debris flow entrained them. Their bones show no evidence of weathering, trampling, scavenging, sorting or transportation prior to debris-flow reworking, which indicates that the animals were probably lying on the bottom of the pond where they lived, or were already partially buried in mud. Previous palynological investigations have shown that the strata of interest at Collecurti were deposited during a climatic trend toward ever increasing cooler conditions. The low richness of the fauna confirms long exposure to harsh climatic and environmental conditions. Two are the plausible causes of the death of the Collecurti animals, i.e., severe cold and/or drought. Taphonomic attributes rule out drought, indicating that the assemblage accumulated in a short time as the result of a mass mortality event, possibly due to a cold snap. There are no other reported examples of Quaternary debris-flow-hosted bonebeds in Europe, probably because this agent of taphonomic accumulation is rarely investigated in high-energy paleogeomorphic settings. It is likely that more such sedimentary events took place in the area, and that similar fossil sites await to be discovered.

Biogeographic provincialism in rodent faunas from the Iberoccitanian Region (southwestern Europe) generates severe diachrony within the Mammalian Neogene (MN) biochronologic scale during the Late Miocene

In order to develop paleoecological studies involving many fossil sites, there is a need to establish a consistent time framework, which enables us to arrange the fossil associations according to a sequence of biotic events and subsequently to test a relationship with paleoenvironmental changes. The nature of the continental fossil record has given rise to much controversy with regard to the establishment of general biostratigraphical scales. Additionally, biochronological scales are sometimes all that can be proposed. The primary goal of the present paper is to present a time arrangement for the Iberoccitanian micromammalian fossil sites from the latest Middle Miocene to the Mio–Pliocene boundary, spanning around 7 million years (approximately 12.61–4.95 Ma). Herein we study over one hundred faunal lists of rodents from the Iberoccitanian Region, compiled from the literature. Previous research has described two biogeographical provinces in our study area: a northern one (Vallès–Penedès and southeast France) and a southern one (all the Iberian basins, except the Vallès–Penedès). We therefore conducted Alroy's Maximum Likelihood Appearance Event Ordination (ML AEO) methodology, applying it to the database compiled for each province. Finally, using available numerical dates for a quarter of the sites, we obtained a calibrated ordination for all localities. In each analysis, the results obtained are roughly coherent with the Mammalian Neogene units (MN) and allow estimation of the numerical ages for the entire set of fossil sites included in the study. Nevertheless, our results show severe diachrony between the two biogeographic provinces of the Iberoccitanian Region in relation to the MN boundaries, which might be linked to the existence of a refuge area associated with more humid environments in the northern province.

Biochronology of Spanish Quaternary small vertebrate faunas

Thousands of fossils of small vertebrates are recorded in one of the most complete stratigraphic sequences of the continental European Pleistocene, in the Sierra de Atapuerca. This sequence, with a few interruptions, spans the last 1.5 million years. The stratigraphic series is recorded in six karstic cavities in the Sierra de Atapuerca. From the oldest record to the most modern one, these are the Sima del Elefante, Gran Dolina, Galería–Zarpazos, Sima de los Huesos, El Portalón and El Mirador. The faunal successions of continental microvertebrates have made it possible to divide the Atapuerca sequence into 7 faunal units (Atapuerca Faunal Units, ATA FUs), which are based on the first and last local appearances of taxa (LO, HO). The Spanish Quaternary small vertebrate faunas are grouped into 5 distinct biozones, from the oldest to the most recent: Allophaiomys pliocaenicus, Allophaiomys lavocati, Allophaiomys chalinei, Iberomys brecciensis and Iberomys cabrerae. These are calibrated with radiometric and palaeomagnetic dating, allowing the proposal of a continental biochronological scale for the Pleistocene of the Iberian Peninsula.

A new quantitative biochronological ordination for the Upper Neogene mammalian localities of Spain

The MN scale is the most widely used biochronological scale for the mammalian fossil record of Europe but at the same time it has brought a high amount of criticism with it. The fossil record of Neogene macromammals from Spain is one of the most complete of the world and provides an interesting test of the MN biochronology. We used maximum likelihood appearance event ordination (ML AEO), a quantitative biochronological method, to provide not only an ordination but also a numerical age estimate for each of the 90 macromammalian fossil faunas that constitute our data base. Originally, only 13 of these localities were numerically dated (mainly by means of paleomagnetism). The ordination of macromammalian fossil faunas matches quite well with the MN chronology at least in the Miocene. The pattern of ordination is less coherent in the Pliocene partly due to the relative poverty of macromammalian fossil sites of this age in Spain. The controversy on whether the age of the first appearance of hipparionine horses in the Iberian Peninsula ( Hipparion dispersal event) was around 10.8–10.7 Ma or 11.1 Ma is discussed. Our estimated MN7/8–MN9 boundary lies between 11.008 and 10.873 Ma. We conclude that the arrival of hipparionine horses in the Iberian Peninsula happened between these two ages and that the oldest record is found in the locality of Nombrevilla 1 with an age of 10.873 Ma.

Les Megacricetodon du gisement karstique miocène moyen de Blanquatère 1 (Pyrénées-Orientales, Sud de la France) : nouvelles espèces, implications biochronologique et phylogénique

Three Megacricetodon species are recognized in the Middle Miocene locality of Blanquatère 1 (Languedoc-Roussillon province, France). Two are new, the small-sized M. tautavelensis nov. sp. the medium to large-sized M. aunayi nov. sp., the third one being the already known M. “collongensis-gersii”, a medium-sized species found in other Miocene localities of the area. Size and morphology differentiate these species. Such a high number of contemporaneous species of the genus Megacricetodon is found for the first time in a Miocene locality in the region and indicate that the evolution of this genus in western Europe is likely more complicated. It may testify both of a biogeographical differentiation and of migration events. According to our calibration charts, the deposit is dated ca. 16 Ma ago. The position of Vieux-Collonges (MN 5) and Sansan (MN 6) on the biochronological scale is also discussed, as well as the estimated age of the biozonal boundaries MN 3/MN 4, MN 4/MN 5 and MN 5/MN 6.

Large- and small-mammal distribution patterns and chronostratigraphic boundaries from the Late Pliocene to the Middle Pleistocene of the Italian peninsula

Over the last 50 years the studies on terrestrial mammals of the Italian peninsula have provided a large volume of data and a more detailed knowledge of faunal events during the Late Pliocene and Quaternary. Moreover geological, sedimentological, palynological and magnetostratigraphical investigations on the Pliocene–Pleistocene continental sedimentary basins have yielded the possibility of a detailed calibration of the faunal successions. Thus, palaeontologists have been able to reconstruct faunal sequences and to propose biochronological scales based on large and small mammals, respectively. In the present contribution an integration of the two biochronological scales is proposed, and the successions of bioevents are carefully compared. This integrated approach allows the constraint of the sequence of large- and small-mammal events in a more reliable way, and therefore it results in a more detailed and consistent chronological use of mammalian assemblages. Particular attention is paid to the faunal changes that correspond to the Middle–Late Pliocene (2.6 ma), Pliocene–Pleistocene (1.8 ma) and Early–Middle Pleistocene (Gauss–Matuyama transition) chronostratigraphical boundaries.