Demberelyin Dashzeveg

Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia

An important transformation in the evolution of mammals was the loss of the epipubic bones. These are elements projecting anteriorly from the pelvic girdle into the abdominal region in a variety of Mesozoic mammals, related tritylodonts, marsupials and monotremes but not in living eutherian (placental) mammals,,. Here we describe a new eutherian from the Late Cretaceous period of Mongolia, and report the first record of epipubic bones in two distinct eutherian lineages. The presence of epipubic bones and other primitive features suggests that these groups occupy a basal position in the Eutheria. It has been argued that the epipubic bones support the pouch in living mammals,,, but epipubic bones have since been related to locomotion and suspension of the litter mass of several attached, lactating offspring. The loss of the epipubic bones in eutherians can be related to the evolution of prolonged gestation, which would not require prolonged external attachment of altricial young. Thus the occurrence of epipubic bones in two Cretaceous eutherians suggests that the dramatic modifications connected with typical placental reproduction,, may have been later events in the evolution of the Eutheria.

Dentition and systematic relationships of Altanius orlovi (Mammalia, Primates) from the early Eocene of Mongolia

Abstract New specimens of Altanius orlovi are described from the type area, Tsagan-Khushu, in Mongolia. These include the first dentary preserving alveoli for anterior teeth, which show the lower dental formula of Altanius to have been 2.1.4.3. Lower incisors were small, equal in size, and nearly vertical in emplacement. The lower canine alveolus is larger than alveoli for the incisors and larger than that for P 1 . Alveoli show P 1 to have been single-rooted and P 2 double-rooted. Upper premolars lack a paraconule, and M 1–2 have a short Nannopithex -fold rather than a full postprotocingulum joining the posterior cingulum. Altanius is one of the smallest primates known. Morphological comparisons with Teilhardina and Cantius indicate that Altanius is more generalized and primitive than other Omomyidae or Adapidae. Altanius is clearly one of the most primitive primates known to date.

New Stratigraphic Subdivision, Depositional Environment, and Age Estimate for the Upper Cretaceous Djadokhta Formation, Southern Ulan Nur Basin, Mongolia

Abstract Studies of key and newly discovered sections of the Upper Cretaceous Djadokhta Formation along the southern margin of the Ulan Nur Basin allow a new subdivision based on lithology. The formation and its members were mapped at both Bayn Dzak, an area that includes the Flaming Cliffs, and Tugrugyin Shireh, an area about 50 km to the northwest of Bayn Dzak. Stratigraphic sections at both localities were remeasured. The considerably enlarged formation comprises a lower Bayn Dzak Member, dominated by moderate reddish orange sands with subordinate mudstone units, and an upper Tugrugyin Member, composed of pale orange to light gray sands. Investigations of key sections at Tsonzh and Alag Teer demonstrate the presence of transitional mudstone lenses between these members within the Djadokhta Formation. Two distinct, sandy, sedimentologic facies are recognized in both members. Cross-bedded intervals, occasionally exhibiting wind-ripple cross lamination, document the presence of a Cretaceous dunefield in the Ulan Nur Basin. Structureless intervals are interpreted to represent wet sandy fluvial deposits and debris flows that moved down the dune faces. In the Bayn Dzak Member, lenses of brownish mudstone are interpreted to represent interdune deposition in shallow ponds by fluvial action. Fluvial action is also represented in the Bayn Dzak Member by beds of caliche, which contain conglomerate at the base but fine upward into limestone. The vertebrate fauna from the Djadokhta Formation is summarized. Although the Bayn Dzak fauna lived somewhat earlier than that from Tugrugyin Shireh based on the superposition of the members, it is not clear how much earlier. The fauna from the Djadokhta Formation has previously been assigned ages from Cenomanian to earliest Maastrichtian. New magnetostratigraphic data document a sequence of normal and reversed magnetozones through the Bayn Dzak Member up into the basal Tugrugyin Member. The presence of reversed magnetozones establishes that the sediments containing the faunas were probably deposited after C34n. The quick stratigraphic succession of normal and reversed magnetozones suggests, but does not clearly establish, that the sediments may have been deposited during the rapid sequence of polarity changes in the late part of the Campanian between about 75 to 71 Ma.

New Avian Remains from the Eocene of Mongolia and the Phylogenetic Position of the Eogruidae (Aves, Gruoidea)

Abstract A well-preserved nearly complete avian tarsometatarsus was collected by the 2002 expedition of the Mongolian Academy of Sciences from upper Eocene deposits exposed at the locality of Alag Tsav in the Eastern Gobi desert (Dornogov Aimag) of Mongolia. The new specimen is identified as part of a proposed Eogruidae clade, although it is unclear whether it is appropriately the holotype of a new species within this clade or referable to a previously named species. The clade Eogruidae has, as its current contents, species named as part of the traditional families Eogruidae + Ergilornithidae, which include several taxa of completely didactylous and apparently flightless birds. Referral of the new fossil to the clade Eogruidae is on the basis of derived reduction/loss of the metatarsal II trochlea. A series of phylogenetic analyses was used to investigate the systematic position of Eogruidae (including the new fossil, IGM 100/1447), which have been proposed to be a dominant part of Eocene to Miocene Asian faunas. First, the Mayr and Clarke (2003) dataset for crown clade Aves was used to investigate placement of Eogruidae within Aves, using a more completely known eogruid, Eogrus aeola, as an exemplar taxon. Eogrus aeola was identical to the new tarsometatarsus for all scored characters. A strict consensus cladogram of three most parsimonious trees from 1000 replicate heuristic searches placed Eogrus aeola in an unresolved polytomy with Psophiidae and Gruidae (Trumpeters and Cranes). Given the results of this analysis, Eogruidae (including IGM 100/1447) was analyzed in the suborder Grues dataset of Livezey (1998). Eogruidae was placed as the sister taxon to an Aramidae + Gruidae clade in the strict consensus cladogram of the eight most parsimonious trees resulting from a branch and bound search. Because monophyly of the traditional order Gruiformes has been repeatedly questioned, and the outgroups used in the original Grues dataset were identified through analyses assuming monophyly, the impact of removing these assumptions was investigated. Placement was robust to both changing outgroup assumptions and to swapping in the more incompletely known IGM 100/1447 as an exemplar for Eogruidae.

New Lizards from the Middle Eocene Mergen Formation, Mongolian Gobi Desert

ZusammenfassungAus der mitteleozänen Mergen-Formation der Gobi/Mongolei werden neue Funde fossiler Echsen beschrieben. Ungefähr 30 isolierte, zahntragende Kiefer sind repräsentativ für mindestens sechs verschiedene Taxa. Darunter befinden sich drei neue Iguania im Sinne nonchamaeleontider Acrodonta, zwei scincomorphe Vertreter mit unsicherer phylogenetischer Stellung und ein Fragment eines recht großwüchsigen Anguimorphen, bei dem es sich um einen Vertreter der Platynota handeln könnte. Diese neuen Echsenfunde tragen zur verbesserten Kenntnis der großen paläogenen Faunenänderung bei, für deren Verständnis besonders die hinzukommenden Daten der fossilen Nonmammalier wichtig sind.AbstractNew lizard fossils are described from the middle Eocene Mergen Formation, eastern Gobi Desert in Mongolia. Some 30 isolated tooth-bearing jaws represent at least six lizard taxa. These include three new iguanians that are nonchamaeleonid acrodontans; two scincomorphs having uncertain relationships within the group; and one large anguimorph that may represent a platynotan taxon. Discovery of these fossil lizards is important for accumulating nonmammalian vertebrate data, in attempting to understand a major faunal change that took place in relation to the drastic uplifting of the Mongolian Plateau in Palaeogene time.

Zaraalestes russelli,a new Tupaiodontine Erinaceid (Mammalia, Lipotyphla) from the Middle Eocene of Mongolia

Abstract A new genus and species of erinaceomorphs, Zaraalestes russelli, is described from the middle Eocenelocalities of Tsagan Tsav and Mergen, southeastern Gobi Desert, Mongolia. This new taxon represents the earliest and most primitive known member of the erinaceid subfamily Tupaiodontinae Butler 1988. Tupaiodon? minutus Matthew & Granger , 1924 from the early Oligocene Hsanda Gol Formation, Mongolia, is included in the genus Zaraalestes and Ictopidium tatalgolensis Sulimski , 1970 is synonymized with minutus. Tupaiodontines show no particularly close relationship to European and North American Paleogene erinaceomorphs and are apparently confined to the middle Eocene — early Oligocene of Mongolia and China.

What isIvanantonia efremovi (Rodentia, Mammalia)?

KurzfassungIvanantonia efremoviShevyreva 1989 aus dem frühen Eozän von Tsagan Khushu (Mongolei) wurde irrtümlich unter dem NamenOrogomys obscurusDashzeveg 1990 beschrieben. Die Form zeigt eine interessante Mischung von ursprünglichen und abgeleiteten Merkmalen: Der InzisivenSchmelz ist zweilagig und hat in der portio interna pauciseriale Hunter-Schreger-Bänder; im Unterkiefer finden sich nur drei Backenzähne; das Kronenmuster der unteren Molaren ist primitiv und ähnelt stark dem vonAlagomys, wobei jedoch das Trigonid im Vergleich zum Talonid weniger reduziert ist. Unterschiede zu anderen primitiven Nagetieren bestehen auch in der Anordnung der Usurfacetten, die auf ein Vorherrschen propalinealer Bewegungen beim Kauvorgang hindeuten. Vergleiche vonInvanantonia mit verschiedenen eozänen und oligozänen Nagern deuten mögliche Beziehungen zuNonomys aus dem Unter-Oligozän Nordamerikas an.AbstractIvanantonia efremoviShevyreva 1989, known from the Tsagan Khushu locality (Early Eocene of Mongolia), erroneously has been described asOrogomys obscurusDashzeveg 1990. This form shows an interesting association of primitive and derived characters: the enamel of the incisors is two-layered and has pauciserial Hunter-Schreger bands in portio interna; the lower tooth row has only three jugal teeth; the tooth pattern of lower molars is primitive and looks very similar to that ofAlagomys, but the trigonid is less reduced with regards to the talonid. It also differs from other primitive rodents in the distribution of wear facets, suggesting that mandibular propalineal movement was pre-eminent during chewing. Comparisons ofIvanantonia with several Eocene-Oligocene rodents indicate possible relationships to the Early Oligocene North American genusNonomys.