The Küçükçekmece vertebrate locality yielded a well-preserved and diverse fauna that was the first Turkish fossil assemblage to be adequately studied by its discoverers, Ahmet Malik and Hamit Nafiz (1933) at that time geology professors at Istanbul University. Indeed, the Marmara Region, where the city of Istanbul and Küçükçekmece are located, is mostly covered of Cainozoic deposits. A review of vertebrate fossil investigations in this region reveals that since the mid-1800s several scholars discovered vertebrate fossils when they explored the region during their “voyage d'étude” in search of evidence concerning the poorly known archaeological, natural and social treasures. Many well-known explorers such as Ami Boué, Auguste Viquesnel, Petr Alexandrovich Tchihatcheff, Franz Toula and later on Nicolae Arabu and Ernest Chaput undertook these “voyages d'études” and they were the first to mention the sporadic occurrence of vertebrate fossils along their itineraries. Since the study of the Küçükçekmece vertebrate fauna by Malik & Nafiz (1933a, b), many other localities have been found, but only a few of them have been the subject of detailed studies. The great extent of Cainozoic deposits in this region indicates great potential for yielding rich vertebrate faunas. In addition, this region is in the transition zone between the Mediterranean and Paratethyan marine realms, on the one hand, and is at the crossroads between the major landmasses of the Old World, on the other. This particular situation is of great interest for palaeobiogeographical research as well as for the dispersal history of many ancient organisms. However, it is also the most populated part of Turkey, and consequently natural outcrops and quarries progressively disappear, being covered by factories and settlements. It is high time that palaeontological research in this region received a new impetus.

The Istanbul region is a part of a bigger continental fragment called the Rhodope-Pontide Fragment. Within this continental fragment, the Istanbul Zone consists, at the base, of a Neoproterozoic middle to high-grade crystalline rocks with relicts of volcanic arc and continental crust, which are not observed in Istanbul itself, but farther east near Zonguldak. This basement is overlain by a continuous, well-developed sedimentary sequence extending from the Lower Ordovician to the Lower Carboniferous. The Carboniferous flysch marks the progress of a shortening event. This event led to the folding and faulting of the Palaeozoic sequence which was intruded by an uppermost Permian granitoid and unconformably overlain by the Upper Permian to Lower Triassic red sandstones and conglomerates. The Triassic series is better formed east of Istanbul showing a typical transgressive development. The Jurassic sequence is absent, most likely as a result of the closure of the Palaeo-Tethys and the resultant generation of the Cimmerides. There is a small outcrop of Lower Cretaceous shallow marine sedimentary rocks and a much more widespread Upper Cretaceous-Lower Eocene clastic, carbonate and andesitic volcanic rocks unconformably covering the Palaeozoic, Triassic and Lower Cretaceous rocks. The pre-Bartonian closure of the Intra-Pontide suture along the Istanbul Zone as a consequence of its collision with the Sakarya Continent created another episode of shortening in this area, an event that was part of the Alpide evolution. The Intra-Pontide suture is the boundary between the Istanbul and Sakarya magmatic arcs in northwestern Turkey. During the Cainozoic, the first post-orogenic structures are Lutetian-Bartonian nummulitic limestones, which themselves are covered by a Paratethyan sequence of Miocene limestones and sandstones of mainly the Vallesian Stage, which include the Küçükçekmece vertebrate bearing horizon. The Pliocene is entirely fluviatile terrestrial clastics. The Pleistocene was deposited on an erosion surface which later became warped and into which the originally fluvial valley of the Bosphorus was entrenched. This valley was invaded by the Sea during the Holocene and caused the refilling of the Black Sea.

The locality of Küçükçekmece has yielded a unique carnivoran fauna representing one of the rare fossil assemblages comprising both marine and terrestrial species. The studied sample comprises thirty-four specimens belonging to three different collections at the Technical University of Istanbul (ITU), Geology Museum of the Istanbul University (IU) and at the National Museum of Natural History of Paris. This low number of fossil remains contrasts with the relatively great taxonomic richness of the fauna, since six families and at least nine species are identified: the ursid Indarctos arctoides (Depéret, 1895), the mustelid Sivaonyx hessicus (Lydekker, 1884), the phocids Cryptophoca sp. and Phocidae gen. et sp. indet., the percrocutid Dinocrocuta senyureki (Ozansoy, 1957), the hyaenid cf. Thalassictis sp., the felids Machairodus aphanistus (Kaup, 1832), Pristifelis sp. cf. P. attica (Wagner, 1857) and Felidae gen. et sp. indet. medium size. A tenth species, a small mustelid identified as Mustela pentelici Gaudry, 1861 by Malik & Nafiz (1933), was probably present. However, the figured (and only?) specimen was destroyed during the 1942 fire at Istanbul University. Most of the species are documented by one or a few specimens, while the phocid material is the most abundant and represents more than half of the described fossils, with many postcranial remains. The list of Carnivora of Küçükçekmece suggests a late Miocene age for the fauna of this site.

The locality Küçükçekmece includes a limited hipparion sample mainly consisting of isolated teeth and some postcranial remains. Using various methods, the teeth and postcranials are separated in two different size groups. The first group, characterized by large size, rich enamel plication, deep and thin plis, double-triple pli caballin, oval protocone with flattened lingual border, absence of lingual hypoconal groove, short and robust metapodials, is related to H. sebastopolitanum Borissiak, 1914 from Sebastopol, Ukraine and it is referred to as H. aff. sebastopolitanum. The second group with very large size, very rich enamel plication, very deep plis, double-multiple pli caballin, oval protocone with flattened lingual border, presence of lingual hypoconal groove, plicated or crenulated flexid's borders in the lower teeth, short and robust metapodials larger than those of the first form, is closer to H. giganteum Gromova, 1952 from Grebeniki, Ukraine and it is identified here as H. aff. giganteum. Hipparion sebastopolitanum and H. giganteum are known from the Ukrainian early and late Vallesian localities of Sebastopol and Grebeniki, respectively. The similarities of the first form with H. cf. sebastopolitanum from the Vallesian localities Pentalophos 1 and Ravin de la Pluie in Axios Valley (Macedonia, Greece), and of the second form with H. aff. giganteum from the terminal Vallesian locality of Nikiti 1 (Chalkidiki, Greece) support a Vallesian age for the Küçükçekmece fauna; more precisely an age from upper early Vallesian to the end of Vallesian is quite possible. The limited data of the dental and postcranial morphology of the Küçükçekmece hipparions indicate a probable forest and warm/humid environment.

Here we describe mandibular, dental, and postcranial remains referable to Rhinocerotidae and Chalicotheriidae (Perissodactyla) originating from the vertebrate localities of Küçükçekmece East and Küçükçekmece West, in Thrace (European Turkey). The four rhinocerotids recognized comprise the early diverging Ronzotherium sp. (one lower molar, reworked from Oligocene deposits; Küçükçekmece West), the two-horned rhinocerotine Ceratotherium neumayri (Osborn, 1900), and two small chilothere aceratheriines: Chilotherium schlosseri (Weber, 1905) and Persiatherium sp. A chalicotheriine chalicotheriid, Kalimantsia sp., is documented by two tooth fragments and an unfused second phalanx of undoubtful affinities in Küçükçekmece West. This occurrence substantiates the record of Kalimantsia, previously restricted to the type locality Kalimantsi-Pehsata, in SW Bulgaria, and allows notably for the first recognition of postcranial remains for this taxon. Although distinct in terms of taxonomic composition and relative abundance, the rhinocerotid assemblages of Küçükçekmece East and Küçükçekmece West are in total agreement with a single biostratigraphical age, estimated to be correlated with the late Vallesian MN10 zone.

The proboscideans found at West-Küçükçekmece (Turkey) are represented by three species, Deinotherium cf. giganteum Kaup, 1829, Choerolophodon pentelici (Gaudry & Lartet, 1856) and “tetralophodont form, gen. and sp. indet.”. This association is characteristic of late Vallesian/Turolian levels in eastern Mediterranean area.

The upper Miocene vertebrate locality of Küçükçekmece West, European Turkey, had provided an artiodactyl assemblage that is rich in species but poor in specimens. The present study allows revising previous artiodactyl lists provided for this site, by recognizing Hippopotamodon cf. antiquus, Dorcatherium maliki n. sp., Palaeotragus sp. (large size), Palaeogiraffa pamiri (Ozansoy, 1965), Bohlinia cf. attica, Gazella cf. ancyrensis, Majoreas cf. elegans, Prostrepsiceros sp., aff. Protoryx cf. enanus, cf. Miotragocerus sp., and Bovidae indet. (large size). The presence of a second suine and a cervid are poorly supported by current data but not excluded. The bulk of this artiodactyl association is also recognized in the Küçükçekmece East fossil assemblage. The Küçükçekmece tragulid is allocated to a new species of a medium sized Dorcatherium with bunoselenodont dentition, long premolars, tricuspid dp2 (p2) and p3, long hypoconid on dp2 and p3, simple distal fossette on p4, and presence of a lingual protocristid on the lower molars. The artiodactyl association of Küçükçekmece points to a Vallesian age, possibly between 9.6–9.4 Ma. The predominance of Dorcatherium and Palaeogiraffa among artiodactyls indicates wooded environmental conditions, whereas the taxonomic spectrum of artiodactyls reveals main influences from both Anatolia and Southern Balkans.

In the context of the present monograph on the late Miocene vertebrate locality of Küçükçekmece, this paper aims to provide a detailed analysis of rodent, lagomorph and insectivore remains. The Küçükçekmece fauna includes three species of rodents (Byzantinia bayraktepensis Ünay, 1980, Spalacidae indet. and Chalicomys jaegeri Kaup, 1832), one lagomorph (Ochotona ozansoyi Sen, 2003) and two insectivores (Schizogalerix sp. and Crusafontina cf. endemica Gibert, 1975). This assemblage is far from reflecting the complete spectrum of these groups in the community of the region. Several common late Miocene taxa are not represented in the material, which was collected by hand picking on the outcrops, not by screen washing of sediment. Among the species recovered, B. bayraktepensis and O. ozansoyi are known elsewhere in latest Astaracian (MN8) and early Vallesian (MN9) localities. The other taxa found at Küçükçekmece are common elements of European Vallesian faunas. Abundance of the beaver C. jaegeri suggests freshwater environment, while the insectivores of this locality indicate rather moist forests and subtropical climatic conditions.