Sevket Sen

Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia

Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world.

The Pleistocene Hominid Site of Ternifine, Algeria: New Results on the Environment, Age, and Human Industries

A new multidisciplinary research program, started in 1981, provided new data on the stratigraphy, fauna, and human industries, as well as the first results on paleomagnetism and sedimentology, for the Ternifine site in Algeria, which yielded the earliest hominid remains known in North Africa. The fossils were deposited in a swamp or lake surrounded by a very open, dry environment. The lake was fed by artesian springs that raised the underlying Miocene sands. Although nothing suggests a camp or butchery site, we discovered the first undisputable bone artifact in this site, the earliest known in this part of Africa. According to paleontological data, 700,000 yr B.P. is a likely age for the Ternifine deposits, which is consistent with the paleomagnetic results.

Magnetostratigraphic calibration of the European Neogene mammal chronology

Abstract This paper presents first a discussion on the status of the subdivisions of the European Neogene mammal chronology and second, it synthesizes all available magnetostratigraphic data from Europe to provide chronological framework for mammal localities, mammalian events and mammalian biochronologic units of the European Neogene. Because of the lack of their rock equivalents, the subdivisions of the European Neogene, based on mammals, have not attained the stage status in terms of reliability, except the Vallesian and Turolian. Therefore they are designated as the European Land Mammal Ages (ELMA). Magnetostratigraphic data on mammal-bearing deposits in Europe is still scarce in time and space; consequently, it is not yet possible to correlate accurately all ELMA and MN zones with the geomagnetic polarity time-scale (GPTS). Nevertheless, several studies dealing with mammal localities (and their deposits) around the Oligocene/Miocene boundary, in the middle and late Miocene provide reliable correlations of some ELMA and MN zone boundaries. Thus, the calibration of the Oligocene/Miocene boundary at the base of Chron C6Cn.2n is in agreement with its age in marine deposits. The well-known Hipparion Datum (Astaracian/Vallesian boundary) is now dated as about 10.8 Ma, occurring slightly above the base of Chron C5n.2n. This paper also reviews magnetostratigraphic correlations of some late Miocene and Pliocene mammal localities in the Paratethys area. Taking into account the chronological assessments in other parts of Europe for some key mammalian events, new correlations with the GPTS have been proposed for these localities. Thus some new ages are suggested for the late Miocene and Pliocene Paratethys stages.

Magnetostratigraphy and biostratigraphy of the neogene deposits of Kastellios Hill (Central Crete, Greece)

Abstract The Kastellios Hill section is situated in central Crete and composed mainly of mudstones and silts deposited in lacustrine, brackish or estuarine environments. Several levels of this section have yielded the remains of mammals, foraminifera, ostracoda, pollen and spores. The palynological analysis shows that the region was forested in the Upper Miocene, with a vegetation confined to climates warmer than the present. The age indicated by foraminifera is Early Tortonian, while the mammals were attributed to Late Vallesian in continental biochronology. Of this section 88 m have been sampled for a magnetostratigraphic study. Several experiments have been made on the magnetic properties of these sediments showing that they are suitable for a paleomagnetic study. Moreover, X-ray diffraction and microprobe analysis of 19 samples regularly distributed over the section show that no major changes occurred in the chemical composition. From 77 separate sites, 241 samples have been demagnetized, thermally (215) or by alternating field (26). The main result of this study is the definition of a long reversed polarity period interrupted by two short normal intervals. This magnetostratigraphic sequence can be correlated, using biostratigraphic data, with a part of Chron 5 r of the geomagnetic time scale; in other words, this section is probably younger than 11.47 My and older than 10.30 My.

Magnetostratigraphy of late Miocene continental deposits in Samos, Greece

Abstract We present a detailed magnetostratigraphic study of the upper part of the Mytilini Formation (Marker Tuffs and Main Bone Beds) of Samos Island (Greece). Seven successive polarity zones have been identified and a correlation with the geomagnetic polarity time scale has established that the sediments of this section were accumulated between 5.7 and 6.8 Ma. According to these results the upper mammalian fossiliferous levels are found within the reversed polarity zone lying in the time interval 6.1–6.4 Ma.

Enigmatic new ungulates from the Early Middle Eocene of central Anatolia, Turkey

Abstract Four new ungulate species described here from the early middle Eocene Uzunçarsidere Formation, near Ankara, Turkey present a phylogenetic and biogeographic puzzle. The four species, known from jaws, teeth, and skull and postcranial fragments, share a suite of diagnostic dental features (selenolophodont molars, all lower molars lacking hypoconulids, premolars with metacones small or absent, and narrow, short premolar talonids) and are included in a single new genus, Hilalia. Hilalia saribeya, H. selanneae, H. sezerorum, and H. robusta are distinguished from each other by size and details of premolar morphology. Cladistic analysis indicates that although Hilalia shares a common ancestor with perissodactyls, hyracoids and some “condylarths” to the exclusion of artiodactyls, its position relative to those taxa is unresolved—the calcaneum lacks derived features of artiodactyl, perissodactyl or hyracoid calcanea, some features of Hilalias molar morphology are convergent with features in some hyracoids, perissodactyls, and selenolophodont “condylarths”, and Hilalia has more primitive premolars than most members of those groups. The affinities of some other members of the Uzunçarsidere mammal fauna, including an embrithopod, marsupials, and a possible proboscidean, have suggested that central Anatolia may have served as a biogeographic crossroads for mammalian dispersal among Asia, Africa, and Europe during the early Paleogene. However, the absence of convincing links between Hilalia and any of the increasingly well-known Paleogene ungulates of Asia, Indo-Pakistan, and Africa, or those of Europe and North America suggests that our understanding of early Paleogene ungulate evolution and biogeography is far from complete.

Rodents and Insectivores from the Upper Miocene of Molayan, Afghanistan

Although Molayan is the richest fossil mammal locality in Afghanistan, only a few species have been studied. This paper describes three rodents (Hystrix aryanensis sp. nov., Parapeolomys sp. and Pseudomeriones latidens sp. nov.) and one insectivore (Erinaceus sp.). Lithostratigraphical correlations and biostratigraphical studies in the Khurdkabul Basin provide evidence that the Molayan locality is younger than three other localities in this basin: Sherullah, Taghar and Ghazgay. In addition, the taxa described here, along with several species of large mammals from Molayan, permit correlations with the Siwalik succession in Pakistan to the east, and with European Neogene mammal ages to the west. The age of the Molayan fauna is concluded to be mid Turolian. Observations on the mammal faunas from the Khurdkabul Basin suggest that the altitude of the area, at present over 2000 m, was much lower during the late Miocene. Uplift of the basin probably occurred no earlier than the ?late Pliocene.

Magnetostratigraphy of early–middle Miocene deposits from east–west trending Alaşehir and Büyük Menderes grabens in western Turkey, and its tectonic implications

Abstract In western Turkey, the Alaşehir and Büyük Menderes grabens form east–west trending major tectonic structures. Their sedimentary fill is important for regional tectonic models for the late Cenozoic evolution of the Aegean region. These deposits are divided into four units dated between the early Miocene and Quaternary. We studied the magnetostratigraphy of two sections in the Alaşehir graben and one in the Büyük Menderes, partly covering the first and second sedimentary units. Detailed palaeomagnetic analysis allowed us to determine ChRM component for these rocks. The Zeytinçayı river and road sections (Alaşehir graben) record several polarity reversals, which are tentatively correlated to the interval C5Cn.3n–C5ADr (approximately between 14.6–16.6 Ma) of the ATNTS2004. This correlation is also supported by palaeontology and radiometric dating of syn-extensional intrusions. In the Eycelli section (Büyük Menderes graben) only three polarity zones are recorded, and their tentative correlation with the interval of C5Bn.1r–C5Br (14.88–15.97 Ma) is in overall in agreement with the record of Eskihisar sporomorph association in this formation. These results place the initiation of the Alaşehir and Büyük Menderes grabens in the early Miocene. The palaeomagnetic declinations from the Alaşehir graben indicate about 25° anticlockwise rotation, whereas that of the Büyük Menderes graben indicate a clockwise rotation of about 30–40°. These contradictory vertical-axis rotations might be explained by detachment faults in the region. In Tertiary formations of western Turkey, contradictory block rotations are common and likely reflect thin-skinned deformation in the area rather than rigid crustal movements. Therefore, average anticlockwise rotations in western Turkey cannot be used as evidence for the model of back-arc spreading in the Aegean region.

Sedimentology of the Miocene evaporitic succession in the north of Çankiri-Çorum basin, central Anatolia, Turkey

The upper Miocene non-marine sediments of the Çankiri-Çorum basin in central Anatolia, have both evaporitic and non-evaporitic successions. These sediments were deposited in an evaporitic lake which had temporary episodes of palustrine conditions in response to seasonal or climatic changes. The successions show different facies such as sulfates, carbonates and siliciclastics. The sulfates comprise primary, reworked and diagenetic gypsum. The primary deposits are predominantly laminated gypsum, bedded gypsum and selenite. The reworked (detrital) gypsum comprises gypsite, gypsarenite, gypsrudite and breccias. The diagenetic type comprises micro- and macrogypsum nodules. The carbonates mainly include clayey limestone, oolitic limestone and dolomite. The siliciclastics comprise red beds and both channel and non-channel, conglomerates and mudstones.Laminated gypsum, composed of alternating gypsum and dolomite, was a result of environmental schizohalinity. Bedded gypsum was precipitated in the deeper part of the lake during high evaporation periods. Chevron-type selenite crystals formed on saline mud flats during the times of aridity, whereas the discoidal-type seen in the organic-rich mudstones occurred in the gypsiferous marshes during the times of humidity. Reworked (detrital) gypsum dominates the lake margin. These formed during periodic wet episodes that caused reworking of primary gypsum. Gypsum nodules occurred as both early and late diagenetic products. Carbonates and siliciclastics were deposited during the freshening periods of the lake.Climatic or seasonal changes were the main causes of the depositional styles of the upper Miocene evaporitic and non-evaporitic lacustrine deposits in Çankiri-Çorum basin. Additionally, the transition upward from alluvial to lake environment implies an important change in drainage patterns that likely occurred as a result of marginal fault activity.

The age of the Molayan mammal locality, Afghanistan

Different opinions have been expressed on the age of the Molayan mammal locality in Afghanistan which has been estimated as middle or late Turolian. This paper reviews the available biochronological data, mainly provided by affinities of Hipparion molayanense, Mesopithecus pentelicus and rodents, and compares this fauna with those from the Siwaliks of Pakistan and of the Aegean area. These comparisons favor the correlation of Molayan with the middle Turolian (MN12).