[F] Nemegt Formation - Nemegtskaya Svita - Mongolia
Mongolia
The Nemegt Formation was discorvered in 1948 and includes the youngest Late Cretaceous sediments known in the Gobi Basin of Mongolia. There are no radiometric data or marine sequences available for this region thereforeit isn\\\'t possible to independently determine the absolute age and its relative age is debatable. The relative age has been estimated as Late Campanian trough Middle Maastrichtian by several authors. The Nemegt Formation overlies the Barun Goyot Formation, but an erosial hiatus separates it from overlying middle Paleocene strata.
In the channel deposits fossilized woods are common. Evidence suggest a warm subhimed climate with seasonal rains. The absence of terrestrial microvertebrates, such as lizards and mammals is striking while megavertebrates represented by large- and mediumsized dinosaurs are abundant and well differentiated. Dinosaur remains mostly occur in the channel-bar sediments. The kind of dinosaurs found in the Nemegt Formation are theropods, sauropods, hadrosaurids, pachycephalosaurs and ankylosaurs. There is an unusually high diversity of theropods. Tarbosaurus bataar and Gallimimus bullatus are represented by ten ore more specimens. The herbivore Saurolophus angustirostris is as common as Tarbosaurus bataar while other species are rare.There are no neoceratopians known from the Nemegt Formation.
The Nemegt locality was chosen as the type locality of the Nemegt Formation. Other than the type locality, the formation is exposed in numerous other parts of the Gobi Altai, Trans-Altai Gobi, and eastern Gobi (e.g., Altan Ula I-IV, Tsagan Khusku, Khermeen Tsav II, Nogon Tsav, Bugin Tsav, and Gurlin Tsav).
Barsbold 1983 The theropod complex consists of tyrannosaurids (Tarbosaurus, Alioramus), an ornithomimid (Gallimimus), a saurornithoidid (Saurornithoides), a dromaeosaurid (Adasaurus), and deinocheirosaurs (Therizinosaurus, Deinocheirus). The end-Cretaceous Mongolian tyrannosaurids are close to the North American forms. It was noted above that one of the earlier representatives of the family (Alectrosaurus) is present in the Baynshirenskaya complex. Ornithomimids are represented by an advanced lineage, also related to the North American forms. Dromaeosaurids are related to the \\\"high-skulled\\\" forms, usually having a wide stratigraphic distribution, but the Nemegtskaya type represents a specific lineage of the family, with the \\\"predatory\\\" pedal ungual having experienced a great reduction to the level of a normal one. Such dromaeosaurids are known so far only in this complex. The Nemegtskaya saurornithoidids are considerably larger than the Djadokhtaskaya forms. However, the large theropods appear to be a more specific element – deinocheirosaurs with non-reduced forelimbs and gigantic ungual phalanges. They are represented by two families, currently known only in this complex from the southwest of the country. Large ungual phalanges also appear in the trans-Baikal, Kazakhstan, and Nigeria (Rozhdestvensky, 1970; Ricqles, 1967), however their differentiation from the Mongolian forms is fairly clear, leading to the possibility about several theropod lineages with gigantic claws in different regions that were not contemporaneous.
The Nemegtskaya theropod complex is fairly unique and is actually differentiated from the stratigraphically earlier Djadokhtaskaya and Barungoyotskaya. It is more characteristic of the upper part of the Cretaceous section in Mongolia. Additionally, in recent times it has been suggested that the sediments should be subdivided into two parts, crowned by the Upper Cretaceous section in the area classified with the single Nemegtskaya Svita in the southwest MPR, based on information from the Presnovodikh fauna and its lithologic-taphonomic properties.
The lower part of the deposit comprises the main bone layer of the major finds from the Nemegtskaya group (actually Nemegtu, Altan Ula, Tsagan Khushu, Gurilin Tsav, etc.). A large dinosaurian, and partly theropod, fauna is contained exactly in this deposit, which was obtained by the paleontological expeditions of the USSR (Efremov, 1949, 1954; Rozhdestvensky, 1957). The upper part is represented by deposits of a somewhat different origin, and is considerably poor with regard to dinosaur remains. A similar thickness has exposures partly in the Nogon Tsav location (here identified under the name Nogon Tsav Svita; Barsbold, 1970, 1972b), and also the upper part of the Cretaceous section at Bugeen Tsav, Khaich, and Naranbulak. The upper part of the Nemegtskaya deposits is differentiated from the lower by a richer fauna, approaching the upper borders with small thicknesses that are covered with paleogenic deposits.
Regional Correlation and Dating. The stratigraphy of the continental Cretaceous of Mongolia is presently fairly developed in this interval, which contained not only invertebrates but also vertebrates, and leads to a wide intercontinental correlation. The conditions and the potential in this respect are highly unequal. With all the wide variety of organic remains in the Cretaceous of the MPR, the wide regional correlation of Cretaceous subdivisions for stratigraphic purposes is often difficult. The reason for this, first of all, is the uniqueness of the continental Cretaceous of Mongolia and the organic groups contained within in as compared to the international stratigraphic standard, which is based mainly on marine deposits and their corresponding fauna.
Furthermore, the difficulties of biostratigraphic correlation with far-reaching reasons based on different organic groups leads to a contradictory interpretation. Apparently, in relation to more or less basic correlations the groups refer to the biostratigraphic indications of those groups, whose genetic type would show at least partially, especially in intercontinental plans. In this sense, among Mongolian Cretaceous dinosaur faunas, the dinosaur and mammals that appeared more varied would have a definite advantage, and with this the fauna of the second half of the Cretaceous.
The intercontinental correlations of Mongolian Cretaceous subdivisions on the basis of the noted fauna is now oriented mainly towards North American faunas and their stratigraphic equivalents. With invertebrates, their correlation is more limited on an analogous level, although fairly wide correlations have been worked out in a series of intervals. The already noted information regarding the freshwater fauna (predominately molluscs) of Mid- and Central Asia may serve as an example. We have now achieved definite progress in the regional and intercontinental correlation of the Cretaceous Mongolian subdivisions. However, the lower part of the Cretaceous of Mongolia is practically excluded from the correlation. The basis for Early Cretaceous layers of Mongolian subdivisions is only conditional in many ways.
In the Lower Cretaceous part, a possible correlation of the Khukhtekskaya horizon is depicted, widely distributed in the MPR (Kalandadze and Kurzanov, 1974), with the Cloverly Formation (Moberly, 1960; Ostrom, 1970) in the Aptian-Albian age interval on the basis of advanced ornithomimids and also dromaeosaurids (Barsbold, Voronin, and Shegallo, 1971; Martinsson, 1971, 1975; Martinson and Shuvalov, 1973; Shuvalov, 1970, 1974, 1975). The information on Early Cretaceous mammals does not deny such a correlation (Beliaeba, Trofimov, and Reshetov, 1974; Dashzeveg, 1975). At the same time, the psittacosaurids occasionally found in this horizon are sometimes considered characteristic of a more ancient, Neocomian, age (Rozhdestvensky, 1971, 1974), which apparently is not completely integrated with their relatively wide stratigraphic distribution (Shuvalov, 1974).
In the Upper Cretaceous, correlation with the North American standard is more or less possible only for the second half. This is linked to the fact that the lower part of the Upper Cretaceous is represented most by marine beds in the compared regions of North America (Cobban and Reeside, 1952; L. S. Russell, 1930, 1964; D. Russell, 1967), while the corresponding intervals in Mongolia [either] include dinosaur remains (Sainshandinskaya horizon), or their presence does not provide very much towards biostratigraphic construction within the country (Baynshirenskaya horizon). At the same time, the second half of the Upper Cretaceous contains a varied fauna of both dinosaurs and mammals in both North America and Mongolia.
According to the information from the few collections of freshwater fauna known in northeastern China as well as southern Primoria (Grabau, 1923; Suzuki, 1943; Yakushina, 1964; Martinsson, Sochava, and Barsbold, 1969), and the conditional dating of the stratigraphic position of the Sainshandinskaya horizon within the limits of the Albian- Cenomanian, a leaning more towards the Lower Cretaceous interval seems acceptable (Martinson, Sochava, and Barsbold, 1969; Barsbold, 1970, 1972b; Martinsson , 1975; Shuvalov, 1975; Sochava, 1975).
The Barungoyotskaya horizon, containing on the southeast specifically faunas of theropods and dinosaurs as a whole, is not very differentiated from the southern and southwestern complexes, characterized by the presence of more primitive ornithomimosaurs. Similar common indications from the theropod fauna as well as the stratigraphic location are in agreement with information from the freshwater groups, supporting the more ancient age of the horizons relative to the Nemegtskaya and possibly the Djadokhtaskaya horizons, in contrast to correlations of earlier works (Maleev, 1952).
The information from ankylosaurs from the Baynshirenskaya horizon and Djadokhtaskaya horizons, as well as protoceratopsians from the Shiregin Gashun localities on the southwest, the deposits of which can be correlated with the Baynshirenskaya on the southeast (Barsbold, 1972a, b; Shuvarov, 1975), is studied as testimony towards the great antiquity of the Bayashirenskaya horizon (Rozhdestvensky, 1971, 1974; Maryanska and Osmólska, 1975; Maryanska, 1977). The freshwater fauna (mostly molluscs) provide a definite possibility for a correlation with analogous formations in Central Asia. Along with this, the correlation of faunal complexes in Fergan and the eastern pre-Urals (Sochava, 1965; Martinsson, 1965) correspond to the Tokubaiskaya (Albian-Cenomanian), and also the Yalovakhskaya and Bostobinskaya Svitas (Lower Senonian) that are taken conditionally to mark the interval of the Baynshirenskaya horizon (Barsbold, 1970, 1972b; Martinsson, 1973, 1975; Sochava, 1975). Instead of this supposition, basing this horizon correlation with consideration of the stratigraphic position given to it by the suite of the same name corresponds to the wide interval between the Cenomanian and Lower Senonian, in that case narrowed to the Cenomanian-Turonian conditionally.
The primitive mammal fauna in the Djadokhtaskaya horizon allows correlation with more or less closely related North American groups. With this as a basis, the conclusion is taken that the fauna from the lower part of the horizon contained in the Djadokhtaskaya Svita deposits fills the blank between the Albian forms from the Trinity Sandstone of Texas and the Campanian from the Judith River deposits of Montana (Kielan-Jaworowska, 1968, 1969, 1970). From here the age of the Djadokhtaskaya horizon, i.e. actually the Djadokhtaskaya Svita, is defined as within the Coniacian- Santonian interval (Kielan-Jaworowska, 1969, 1970, 1974a, b, 1975a, b).
The dating of the upper part of the Djadokhtaskaya horizon, represented by the Barungoyotskaya Svita, is also based on information from the mammalian fauna of Mongolia and North America and the consideration of the types between the earliest (Djadokhtaskaya) and later (Barungoyotskaya) faunas of the horizon itself. In North America, stratigraphic analogs of the Barungoyotskaya Svita such as the Milk River, Judith River, and [Oldman Formations] will provide information (Cobban and Reeside, 1952; Russell, 1964, 1970; Ostrom, 1965; Morris, 1967; Sloan, 1970; Fox, 1970, 1971, 1971) from which its age was placed within the limits of the Campanian (Kielan-Jaworowska, 1974a, b, 1975a, b; Gradzinsky, Kielan-Jaworowska, and Maryanska, 1977). In this manner, the lower and upper age limits of the Djadokhtaskaya horizon are considered to correspond to the Lower Senonian and Campanian.
The correlation of the Nemegtskaya horizon is built predominately on the information from the relations between the types of dinosaurian fauna, whose evolutionary lineages reach down to the earlier complexes. At the same time, the uniqueness of the theropods and other dinosaurs, the character of the complexes of the freshwater fauna, and the stratigraphic positions of the Nemegtskaya and Nogontsavskaya horizon deposits testify to the fact that the Nemegtskaya horizon crowns the Upper Cretaceous section in the southwestern MPR, and apparently has a higher stratigraphic position in Central Asia (Barsbold, 1969, 1972b). The upper part of the continental Cretaceous of Mongolia, with very rare mammal finds, must be correlated with the corresponding North American subdivisions. The absence of true ceratopsids in the MPR, and the close similarity between the Mongolian and North American tyrannosaurids and hadrosaurids, led to thoughts of the possibility that it was correlated with the Edmonton Formation, which itself is correlated with the lower part of the Lance Formation (Cobban and Reeside, 1952; Russell, 1964; Russell and Chamney, 1967), and the dating of the Nemegtskaya deposits as Maastrichtian ( Rozhdestvensky, 1957a, b, 1965, 1968, 1974). Biostratigraphic information from the freshwater fauna also led to the acceptance of a similar age, sometimes bounded by the upper Senonian (Martinsson, Sochava, and Barsbold , 1969; Barsbold, 1970, 1972b; Stankevich and Sochava , 1974; Martinsson, 1973, 1975; Shuvalov, 1975; Kielan-Jaworowksa and Sochava, 1969).
The correlation with the Edmonton Formation (Belly River and others) now seems [supported] by new information about the Mongolian dinosaur fauna (Osmólska, Roniewicz, and Barsbold, 1972). At the same time, the dating of the correlated North American subdivisions have gradually been modified, and the stratigraphic level corresponding to the Edmontonian stage is now defined as belonging to the Upper Campanian-Lower Maastrichtian interval, which is also supported by radiometric information (Morris, 1967). A similar interval is also supported for the Nemegtskaya faunal complex (Osmólska, Roniewicz, and Barsbold, 1972; Maryanska and Osmólska, 1974, 1975; Gradzinsky, Kielan-Jaworowska, and Maryanska, 1977; Maryanska, 1977). In this manner, the regional and intercontinental correlations of Cretaceous stratigraphic horizons of Mongolia that form the currently identified suites are taken on the basis of various faunas. The lowest of the connecting faunal deposits, that of the Khukhtekskaya horizon within the Aptian-Albian interval, more or less corresponds to the stratigraphic level of the Cloverly Formation of Montana.
The following Sainshandinskaya horizon, near the border of the Lower and Middle Cretaceous, is dated as Aptian-Cenomanian based on the similarity of the freshwater molluscs with those distributed in northeastern China and, as has been noted, is similarly relegated to the Lower Cretaceous. The Baynshirenskaya horizon, according to information from the freshwater fauna, also corresponds to the Cenomanian-Lower Senonian interval, established for the Tokubaiskaya, Yalovakhskaya, and Bostobinskaya Svitas in the region of Central Asia (Fergana, trans pre-Urals), and possibly corresponds to the Cenomanian- Turonian interval. The lower part of the Djadokhtaskaya Svita of the horizon of the same name is probably correlated with the Lower Senonian, based on correlation with North America, however its interrelationships with the Baynshirenskayahorizon are not entirely clear. Most likely, the Baynshirenskaya horizon and Svita are actually older than the Djadokhtaskaya Svita, affirming the Cenomanian-Turonian age of the former. The Barungoyotskaya Svita, corresponding to the upper part of the Djadokhtaskaya horizon, is accepted as Campanian by correlation with North America. Analogous correlations lead to the acceptance of the Campanian-Lower Maastrichtian interval for the Nemegtskaya horizon.
Adasaurus mongoliensis - Coelurosauria Dromaeosauridae - Cretaceous Late Maastrichtian
Albertosaurus novojilovi - Tyrannosaurinae Tarbosaurini - Cretaceous Late
Alioramus altai - Tyrannosauridae Tyrannosaurinae- Cretaceous Late Maastrichtian
Anserimimus planinychus - Ornithomimosauria Ornithomimidae - Cretaceous Late Campanian Maastrichtian
Bagaraatan ostromi - Tetanurae Maniraptora - Cretaceous Late
Barsboldia sicinskii - Lambeosaurinae Incertae Sedis - Cretaceous Late Campanian Maastrichtian
Borogovia gracilicrus - Coelurosauria Troodontidae - Cretaceous Late Campanian Maastrichtian
Deinocheirus mirificus - Tetanurae Coelurosauria - Cretaceous Late ?Campanian Maastrichtian
Elmisaurus rarus - Oviraptorosauria Caenagnathidae - Cretaceous Late Campanian Maastrichtian
Gallimimus bullatus - Ornithomimosauria Ornithomimidae - Cretaceous Late Campanian Maastrichtian
Gorgosaurus lancinator - Tyrannosauria Tyrannosauridae - Cretaceous Late Campanian Maastrichtian
Gorgosaurus novojilovi - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian ?Maastrichtian
Gurilynia nessovi ~/~ - Ornithothoraces Enantiornithes - Cretaceous Late Maastrichtian
Homalocephale calathoceros - Pachycephalosauria Homalocephalidae - Cretaceous Late Campanian Maastrichtian
Ingenia yanshini (1) - Oviraptorosauria Ingeniidae - Cretaceous Late Campanian Maastrichtian
Jenghizkhan bataar - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian Maastrichtian
Judinornis nogontsavensis ~/~ - Ornithurae [Hesperonithiformes] [Baptornithidae] - Cretaceous Late Maastrichtian
Maleevosaurus novojilovi - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian ?Maastrichtian
Mononykus olecranus ~/~ - Avialae Alvarezsauridae - Cretaceous Late Campanian
Nemegtia barsboldi - [Preoccupied by an ostracod from the same formation] (Lü, Tomida, Azuma, Dong, and Lee, 2005)
Nemegtosaurus mongoliensis - Diplodocidae Dicraeosaurinae - Cretaceous Late ?Campanian Maastrichtian
Opisthocoelicaudia skarzynskii - Sauropoda Titanosauria - Cretaceous Late ?Campanian Maastrichtian
Oviraptor mongoliensis - Oviraptorosauria Oviraptoridae - Cretaceous Late Campanian Maastrichtian
Prenocephale prenes - Pachycephalosauria Pachycephalosauridae - Cretaceous Late Campanian Maastrichtian
Rinchenia mongoliensis - Oviraptorosauria Oviraptoridae - Cretaceous Late Campanian Maastrichtian
Saurolophus angustirostris - Gryposaurini Saurolophini - Cretaceous Late Campanian Maastrichtian
Saurornithoides junior - Maniraptora Troodontidae - Cretaceous Late ?Campanian Maastrichtian
Tarbosaurus bataar - Tyrannosauria Tyrannosauridae - Cretaceous Late Campanian Maastrichtian
Tarbosaurus efremovi - Tyrannosauria Tyrannosauridae - Cretaceous Late Campanian Maastrichtian
Tarchia gigantea - Ankylosauria Ankylosauridae - Cretaceous Late Campanian Maastrichtian
Therizinosaurus cheloniformis - Therizinosauroidea Therizinosauridae - Cretaceous Late ?Campanian Maastrichtian
Tochisaurus nemegtensis - Maniraptora Troodontidae - Cretaceous Late ?Campanian Maastrichtian
Tyrannosaurus bataar - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian Maastrichtian
Zanabazar junior - Maniraptora Troodontidae - Cretaceous Late ?Campanian Maastrichtian
Hadrosaurid indet. - Ornithopoda Hadrosauridae - Cretaceous Late Campanian Maastrichtian
Oviraptorid indet. - Theropoda Oviraptoridae - Cretaceous Late Campanian Maastrichtian
Theropoda indet. - Theropoda - Cretaceous Late Campanian Maastrichtian
The Nemegt Formation was discorvered in 1948 and includes the youngest Late Cretaceous sediments known in the Gobi Basin of Mongolia. There are no radiometric data or marine sequences available for this region thereforeit isn\\\'t possible to independently determine the absolute age and its relative age is debatable. The relative age has been estimated as Late Campanian trough Middle Maastrichtian by several authors. The Nemegt Formation overlies the Barun Goyot Formation, but an erosial hiatus separates it from overlying middle Paleocene strata.
In the channel deposits fossilized woods are common. Evidence suggest a warm subhimed climate with seasonal rains. The absence of terrestrial microvertebrates, such as lizards and mammals is striking while megavertebrates represented by large- and mediumsized dinosaurs are abundant and well differentiated. Dinosaur remains mostly occur in the channel-bar sediments. The kind of dinosaurs found in the Nemegt Formation are theropods, sauropods, hadrosaurids, pachycephalosaurs and ankylosaurs. There is an unusually high diversity of theropods. Tarbosaurus bataar and Gallimimus bullatus are represented by ten ore more specimens. The herbivore Saurolophus angustirostris is as common as Tarbosaurus bataar while other species are rare.There are no neoceratopians known from the Nemegt Formation.
The Nemegt locality was chosen as the type locality of the Nemegt Formation. Other than the type locality, the formation is exposed in numerous other parts of the Gobi Altai, Trans-Altai Gobi, and eastern Gobi (e.g., Altan Ula I-IV, Tsagan Khusku, Khermeen Tsav II, Nogon Tsav, Bugin Tsav, and Gurlin Tsav).
Barsbold 1983 The theropod complex consists of tyrannosaurids (Tarbosaurus, Alioramus), an ornithomimid (Gallimimus), a saurornithoidid (Saurornithoides), a dromaeosaurid (Adasaurus), and deinocheirosaurs (Therizinosaurus, Deinocheirus). The end-Cretaceous Mongolian tyrannosaurids are close to the North American forms. It was noted above that one of the earlier representatives of the family (Alectrosaurus) is present in the Baynshirenskaya complex. Ornithomimids are represented by an advanced lineage, also related to the North American forms. Dromaeosaurids are related to the \\\"high-skulled\\\" forms, usually having a wide stratigraphic distribution, but the Nemegtskaya type represents a specific lineage of the family, with the \\\"predatory\\\" pedal ungual having experienced a great reduction to the level of a normal one. Such dromaeosaurids are known so far only in this complex. The Nemegtskaya saurornithoidids are considerably larger than the Djadokhtaskaya forms. However, the large theropods appear to be a more specific element – deinocheirosaurs with non-reduced forelimbs and gigantic ungual phalanges. They are represented by two families, currently known only in this complex from the southwest of the country. Large ungual phalanges also appear in the trans-Baikal, Kazakhstan, and Nigeria (Rozhdestvensky, 1970; Ricqles, 1967), however their differentiation from the Mongolian forms is fairly clear, leading to the possibility about several theropod lineages with gigantic claws in different regions that were not contemporaneous.
The Nemegtskaya theropod complex is fairly unique and is actually differentiated from the stratigraphically earlier Djadokhtaskaya and Barungoyotskaya. It is more characteristic of the upper part of the Cretaceous section in Mongolia. Additionally, in recent times it has been suggested that the sediments should be subdivided into two parts, crowned by the Upper Cretaceous section in the area classified with the single Nemegtskaya Svita in the southwest MPR, based on information from the Presnovodikh fauna and its lithologic-taphonomic properties.
The lower part of the deposit comprises the main bone layer of the major finds from the Nemegtskaya group (actually Nemegtu, Altan Ula, Tsagan Khushu, Gurilin Tsav, etc.). A large dinosaurian, and partly theropod, fauna is contained exactly in this deposit, which was obtained by the paleontological expeditions of the USSR (Efremov, 1949, 1954; Rozhdestvensky, 1957). The upper part is represented by deposits of a somewhat different origin, and is considerably poor with regard to dinosaur remains. A similar thickness has exposures partly in the Nogon Tsav location (here identified under the name Nogon Tsav Svita; Barsbold, 1970, 1972b), and also the upper part of the Cretaceous section at Bugeen Tsav, Khaich, and Naranbulak. The upper part of the Nemegtskaya deposits is differentiated from the lower by a richer fauna, approaching the upper borders with small thicknesses that are covered with paleogenic deposits.
Regional Correlation and Dating. The stratigraphy of the continental Cretaceous of Mongolia is presently fairly developed in this interval, which contained not only invertebrates but also vertebrates, and leads to a wide intercontinental correlation. The conditions and the potential in this respect are highly unequal. With all the wide variety of organic remains in the Cretaceous of the MPR, the wide regional correlation of Cretaceous subdivisions for stratigraphic purposes is often difficult. The reason for this, first of all, is the uniqueness of the continental Cretaceous of Mongolia and the organic groups contained within in as compared to the international stratigraphic standard, which is based mainly on marine deposits and their corresponding fauna.
Furthermore, the difficulties of biostratigraphic correlation with far-reaching reasons based on different organic groups leads to a contradictory interpretation. Apparently, in relation to more or less basic correlations the groups refer to the biostratigraphic indications of those groups, whose genetic type would show at least partially, especially in intercontinental plans. In this sense, among Mongolian Cretaceous dinosaur faunas, the dinosaur and mammals that appeared more varied would have a definite advantage, and with this the fauna of the second half of the Cretaceous.
The intercontinental correlations of Mongolian Cretaceous subdivisions on the basis of the noted fauna is now oriented mainly towards North American faunas and their stratigraphic equivalents. With invertebrates, their correlation is more limited on an analogous level, although fairly wide correlations have been worked out in a series of intervals. The already noted information regarding the freshwater fauna (predominately molluscs) of Mid- and Central Asia may serve as an example. We have now achieved definite progress in the regional and intercontinental correlation of the Cretaceous Mongolian subdivisions. However, the lower part of the Cretaceous of Mongolia is practically excluded from the correlation. The basis for Early Cretaceous layers of Mongolian subdivisions is only conditional in many ways.
In the Lower Cretaceous part, a possible correlation of the Khukhtekskaya horizon is depicted, widely distributed in the MPR (Kalandadze and Kurzanov, 1974), with the Cloverly Formation (Moberly, 1960; Ostrom, 1970) in the Aptian-Albian age interval on the basis of advanced ornithomimids and also dromaeosaurids (Barsbold, Voronin, and Shegallo, 1971; Martinsson, 1971, 1975; Martinson and Shuvalov, 1973; Shuvalov, 1970, 1974, 1975). The information on Early Cretaceous mammals does not deny such a correlation (Beliaeba, Trofimov, and Reshetov, 1974; Dashzeveg, 1975). At the same time, the psittacosaurids occasionally found in this horizon are sometimes considered characteristic of a more ancient, Neocomian, age (Rozhdestvensky, 1971, 1974), which apparently is not completely integrated with their relatively wide stratigraphic distribution (Shuvalov, 1974).
In the Upper Cretaceous, correlation with the North American standard is more or less possible only for the second half. This is linked to the fact that the lower part of the Upper Cretaceous is represented most by marine beds in the compared regions of North America (Cobban and Reeside, 1952; L. S. Russell, 1930, 1964; D. Russell, 1967), while the corresponding intervals in Mongolia [either] include dinosaur remains (Sainshandinskaya horizon), or their presence does not provide very much towards biostratigraphic construction within the country (Baynshirenskaya horizon). At the same time, the second half of the Upper Cretaceous contains a varied fauna of both dinosaurs and mammals in both North America and Mongolia.
According to the information from the few collections of freshwater fauna known in northeastern China as well as southern Primoria (Grabau, 1923; Suzuki, 1943; Yakushina, 1964; Martinsson, Sochava, and Barsbold, 1969), and the conditional dating of the stratigraphic position of the Sainshandinskaya horizon within the limits of the Albian- Cenomanian, a leaning more towards the Lower Cretaceous interval seems acceptable (Martinson, Sochava, and Barsbold, 1969; Barsbold, 1970, 1972b; Martinsson , 1975; Shuvalov, 1975; Sochava, 1975).
The Barungoyotskaya horizon, containing on the southeast specifically faunas of theropods and dinosaurs as a whole, is not very differentiated from the southern and southwestern complexes, characterized by the presence of more primitive ornithomimosaurs. Similar common indications from the theropod fauna as well as the stratigraphic location are in agreement with information from the freshwater groups, supporting the more ancient age of the horizons relative to the Nemegtskaya and possibly the Djadokhtaskaya horizons, in contrast to correlations of earlier works (Maleev, 1952).
The information from ankylosaurs from the Baynshirenskaya horizon and Djadokhtaskaya horizons, as well as protoceratopsians from the Shiregin Gashun localities on the southwest, the deposits of which can be correlated with the Baynshirenskaya on the southeast (Barsbold, 1972a, b; Shuvarov, 1975), is studied as testimony towards the great antiquity of the Bayashirenskaya horizon (Rozhdestvensky, 1971, 1974; Maryanska and Osmólska, 1975; Maryanska, 1977). The freshwater fauna (mostly molluscs) provide a definite possibility for a correlation with analogous formations in Central Asia. Along with this, the correlation of faunal complexes in Fergan and the eastern pre-Urals (Sochava, 1965; Martinsson, 1965) correspond to the Tokubaiskaya (Albian-Cenomanian), and also the Yalovakhskaya and Bostobinskaya Svitas (Lower Senonian) that are taken conditionally to mark the interval of the Baynshirenskaya horizon (Barsbold, 1970, 1972b; Martinsson, 1973, 1975; Sochava, 1975). Instead of this supposition, basing this horizon correlation with consideration of the stratigraphic position given to it by the suite of the same name corresponds to the wide interval between the Cenomanian and Lower Senonian, in that case narrowed to the Cenomanian-Turonian conditionally.
The primitive mammal fauna in the Djadokhtaskaya horizon allows correlation with more or less closely related North American groups. With this as a basis, the conclusion is taken that the fauna from the lower part of the horizon contained in the Djadokhtaskaya Svita deposits fills the blank between the Albian forms from the Trinity Sandstone of Texas and the Campanian from the Judith River deposits of Montana (Kielan-Jaworowska, 1968, 1969, 1970). From here the age of the Djadokhtaskaya horizon, i.e. actually the Djadokhtaskaya Svita, is defined as within the Coniacian- Santonian interval (Kielan-Jaworowska, 1969, 1970, 1974a, b, 1975a, b).
The dating of the upper part of the Djadokhtaskaya horizon, represented by the Barungoyotskaya Svita, is also based on information from the mammalian fauna of Mongolia and North America and the consideration of the types between the earliest (Djadokhtaskaya) and later (Barungoyotskaya) faunas of the horizon itself. In North America, stratigraphic analogs of the Barungoyotskaya Svita such as the Milk River, Judith River, and [Oldman Formations] will provide information (Cobban and Reeside, 1952; Russell, 1964, 1970; Ostrom, 1965; Morris, 1967; Sloan, 1970; Fox, 1970, 1971, 1971) from which its age was placed within the limits of the Campanian (Kielan-Jaworowska, 1974a, b, 1975a, b; Gradzinsky, Kielan-Jaworowska, and Maryanska, 1977). In this manner, the lower and upper age limits of the Djadokhtaskaya horizon are considered to correspond to the Lower Senonian and Campanian.
The correlation of the Nemegtskaya horizon is built predominately on the information from the relations between the types of dinosaurian fauna, whose evolutionary lineages reach down to the earlier complexes. At the same time, the uniqueness of the theropods and other dinosaurs, the character of the complexes of the freshwater fauna, and the stratigraphic positions of the Nemegtskaya and Nogontsavskaya horizon deposits testify to the fact that the Nemegtskaya horizon crowns the Upper Cretaceous section in the southwestern MPR, and apparently has a higher stratigraphic position in Central Asia (Barsbold, 1969, 1972b). The upper part of the continental Cretaceous of Mongolia, with very rare mammal finds, must be correlated with the corresponding North American subdivisions. The absence of true ceratopsids in the MPR, and the close similarity between the Mongolian and North American tyrannosaurids and hadrosaurids, led to thoughts of the possibility that it was correlated with the Edmonton Formation, which itself is correlated with the lower part of the Lance Formation (Cobban and Reeside, 1952; Russell, 1964; Russell and Chamney, 1967), and the dating of the Nemegtskaya deposits as Maastrichtian ( Rozhdestvensky, 1957a, b, 1965, 1968, 1974). Biostratigraphic information from the freshwater fauna also led to the acceptance of a similar age, sometimes bounded by the upper Senonian (Martinsson, Sochava, and Barsbold , 1969; Barsbold, 1970, 1972b; Stankevich and Sochava , 1974; Martinsson, 1973, 1975; Shuvalov, 1975; Kielan-Jaworowksa and Sochava, 1969).
The correlation with the Edmonton Formation (Belly River and others) now seems [supported] by new information about the Mongolian dinosaur fauna (Osmólska, Roniewicz, and Barsbold, 1972). At the same time, the dating of the correlated North American subdivisions have gradually been modified, and the stratigraphic level corresponding to the Edmontonian stage is now defined as belonging to the Upper Campanian-Lower Maastrichtian interval, which is also supported by radiometric information (Morris, 1967). A similar interval is also supported for the Nemegtskaya faunal complex (Osmólska, Roniewicz, and Barsbold, 1972; Maryanska and Osmólska, 1974, 1975; Gradzinsky, Kielan-Jaworowska, and Maryanska, 1977; Maryanska, 1977). In this manner, the regional and intercontinental correlations of Cretaceous stratigraphic horizons of Mongolia that form the currently identified suites are taken on the basis of various faunas. The lowest of the connecting faunal deposits, that of the Khukhtekskaya horizon within the Aptian-Albian interval, more or less corresponds to the stratigraphic level of the Cloverly Formation of Montana.
The following Sainshandinskaya horizon, near the border of the Lower and Middle Cretaceous, is dated as Aptian-Cenomanian based on the similarity of the freshwater molluscs with those distributed in northeastern China and, as has been noted, is similarly relegated to the Lower Cretaceous. The Baynshirenskaya horizon, according to information from the freshwater fauna, also corresponds to the Cenomanian-Lower Senonian interval, established for the Tokubaiskaya, Yalovakhskaya, and Bostobinskaya Svitas in the region of Central Asia (Fergana, trans pre-Urals), and possibly corresponds to the Cenomanian- Turonian interval. The lower part of the Djadokhtaskaya Svita of the horizon of the same name is probably correlated with the Lower Senonian, based on correlation with North America, however its interrelationships with the Baynshirenskayahorizon are not entirely clear. Most likely, the Baynshirenskaya horizon and Svita are actually older than the Djadokhtaskaya Svita, affirming the Cenomanian-Turonian age of the former. The Barungoyotskaya Svita, corresponding to the upper part of the Djadokhtaskaya horizon, is accepted as Campanian by correlation with North America. Analogous correlations lead to the acceptance of the Campanian-Lower Maastrichtian interval for the Nemegtskaya horizon.
Adasaurus mongoliensis - Coelurosauria Dromaeosauridae - Cretaceous Late Maastrichtian
Albertosaurus novojilovi - Tyrannosaurinae Tarbosaurini - Cretaceous Late
Alioramus altai - Tyrannosauridae Tyrannosaurinae- Cretaceous Late Maastrichtian
Anserimimus planinychus - Ornithomimosauria Ornithomimidae - Cretaceous Late Campanian Maastrichtian
Bagaraatan ostromi - Tetanurae Maniraptora - Cretaceous Late
Barsboldia sicinskii - Lambeosaurinae Incertae Sedis - Cretaceous Late Campanian Maastrichtian
Borogovia gracilicrus - Coelurosauria Troodontidae - Cretaceous Late Campanian Maastrichtian
Deinocheirus mirificus - Tetanurae Coelurosauria - Cretaceous Late ?Campanian Maastrichtian
Elmisaurus rarus - Oviraptorosauria Caenagnathidae - Cretaceous Late Campanian Maastrichtian
Gallimimus bullatus - Ornithomimosauria Ornithomimidae - Cretaceous Late Campanian Maastrichtian
Gorgosaurus lancinator - Tyrannosauria Tyrannosauridae - Cretaceous Late Campanian Maastrichtian
Gorgosaurus novojilovi - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian ?Maastrichtian
Gurilynia nessovi ~/~ - Ornithothoraces Enantiornithes - Cretaceous Late Maastrichtian
Homalocephale calathoceros - Pachycephalosauria Homalocephalidae - Cretaceous Late Campanian Maastrichtian
Ingenia yanshini (1) - Oviraptorosauria Ingeniidae - Cretaceous Late Campanian Maastrichtian
Jenghizkhan bataar - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian Maastrichtian
Judinornis nogontsavensis ~/~ - Ornithurae [Hesperonithiformes] [Baptornithidae] - Cretaceous Late Maastrichtian
Maleevosaurus novojilovi - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian ?Maastrichtian
Mononykus olecranus ~/~ - Avialae Alvarezsauridae - Cretaceous Late Campanian
Nemegtia barsboldi - [Preoccupied by an ostracod from the same formation] (Lü, Tomida, Azuma, Dong, and Lee, 2005)
Nemegtosaurus mongoliensis - Diplodocidae Dicraeosaurinae - Cretaceous Late ?Campanian Maastrichtian
Opisthocoelicaudia skarzynskii - Sauropoda Titanosauria - Cretaceous Late ?Campanian Maastrichtian
Oviraptor mongoliensis - Oviraptorosauria Oviraptoridae - Cretaceous Late Campanian Maastrichtian
Prenocephale prenes - Pachycephalosauria Pachycephalosauridae - Cretaceous Late Campanian Maastrichtian
Rinchenia mongoliensis - Oviraptorosauria Oviraptoridae - Cretaceous Late Campanian Maastrichtian
Saurolophus angustirostris - Gryposaurini Saurolophini - Cretaceous Late Campanian Maastrichtian
Saurornithoides junior - Maniraptora Troodontidae - Cretaceous Late ?Campanian Maastrichtian
Tarbosaurus bataar - Tyrannosauria Tyrannosauridae - Cretaceous Late Campanian Maastrichtian
Tarbosaurus efremovi - Tyrannosauria Tyrannosauridae - Cretaceous Late Campanian Maastrichtian
Tarchia gigantea - Ankylosauria Ankylosauridae - Cretaceous Late Campanian Maastrichtian
Therizinosaurus cheloniformis - Therizinosauroidea Therizinosauridae - Cretaceous Late ?Campanian Maastrichtian
Tochisaurus nemegtensis - Maniraptora Troodontidae - Cretaceous Late ?Campanian Maastrichtian
Tyrannosaurus bataar - Tyrannosaurinae Tarbosaurini - Cretaceous Late Campanian Maastrichtian
Zanabazar junior - Maniraptora Troodontidae - Cretaceous Late ?Campanian Maastrichtian
Hadrosaurid indet. - Ornithopoda Hadrosauridae - Cretaceous Late Campanian Maastrichtian
Oviraptorid indet. - Theropoda Oviraptoridae - Cretaceous Late Campanian Maastrichtian
Theropoda indet. - Theropoda - Cretaceous Late Campanian Maastrichtian