Browsing by Author "Mongolyn Shinzhlekh Ukhaany Akademi."
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Item Amphicticeps and Amphicynodon (Arctoidea, Carnivora) from Hsanda Gol Formation, central Mongolia, and phylogeny of basal arctoids with comments on zoogeography. American Museum novitates ; no. 3483(New York, NY : American Museum of Natural History, 2005) Wang, Xiaoming, 1957-; McKenna, Malcolm C.; Dashzėvėg, Dėmbėrėliĭn.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlekh Ukhaany Akademi.; Central Asiatic Expeditions (1921-1930)Amphicticeps shackelfordi and Amphicynodon teilhardi are two small carnivorans from the early Oligocene Hsanda Gol Formation of central Mongolia, and as basal arctoids (infraorder Arctoidea) in Asia, feature unique combinations of morphologies that offer insights into early diversification and zoogeography of the arctoids. Lack of adequate study of Amphicticeps and incomplete knowledge about Amphicynodon, however, prevented them from being figured in the discussions of arctoid relationships. New associated dental and cranial materials collected during recent expeditions in the 1990s substantially enrich our knowledge of the two genera and their stratigraphic positions, and serve as an impetus for a study of their phylogenetic relationships in the broad perspective of basal Arctoidea. Hsanda Gol arctoids are represented by six small- to medium-sized species: Amphicticeps shackelfordi Matthew and Granger 1924, A. dorog, n.sp., A. makhchinus, n.sp., Amphicynodon teilhardi Matthew and Granger 1924,? Cephalogale sp., and Pyctis inamatus Babbitt, 1999. The three species of Amphicticeps apparently form an endemic clade confined to central Asia, whose zoogeographic origin is currently unknown. Amphicynodon has a much higher diversity in Europe than in Asia, and phylogenetically the Asian A. teilhardi seems to be nested within the European congeneric species, indicating an eastward dispersal for this group, linking the European "Grande Coupure" and the Asian "Mongolian Reconstruction" events. To avoid excessive homoplasies in crown groups, we attempted a phylogenetic reconstruction based mostly on stem arctoids. Twenty genera of primitive arctoids occupying basal positions of nearly all major clades are selected for the analysis. The resulting tree, based on 39 characters, approximates the initial divergence of the arctoids. The traditionally dichotomous Arctoidea, formed by sister clades Ursida and Mustelida, is recovered in our analysis. Mustelida is also largely dichotomous with mustelid-like forms on one side and procyonidlike forms on the other. Despite its rather hypercarnivorous dentition, Amphicticeps is found on the Ursida side of the arctoids, although support for such a topology is relatively weak. Amphicynodon is a stem taxon of the Ursida and is a sister to an ursid-pinniped clade.Item Erketu ellisoni, a long-necked sauropod from Bor Guvé (Dornogov Aimag, Mongolia). American Museum novitates ; no. 3508(New York, NY : American Museum of Natural History, 2006) Ksepka, Daniel T.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlekh Ukhaany Akademi.The first specimen of the new sauropod Erketu ellisoni, from the Lower Cretaceous of the eastern Gobi of Dornogov, Mongolia, is described here. The specimen comprises a well-preserved articulated anterior cervical series, an articulated lower hindlimb, and a sternal plate. This sauropod displays a unique combination of features including low, bifid neural spines, elongate cervical centra, and crescent-shaped sternal plates. Computed tomography imaging reveals the vertebrae were extensively invaded with pneumatic camellae. The holotype individual of Erketu was of modest mass relative to other neosauropods, but had an extremely elongate neck. Phylogenetic analysis indicates Erketu is a member of the Somphospondyli and may belong to a more exclusive clade therein.Item New avian remains from the Eocene of Mongolia and the phylogenetic position of the Eogruidae (Aves, Gruoidea). American Museum novitates ; no. 3494(New York, NY : American Museum of Natural History, 2005) Clarke, Julia A.; Norell, Mark.; Dashzėvėg, Dėmbėrėliĭn.; Mongolyn Shinzhlekh Ukhaany Akademi.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.Item A small derived theropod from Öösh, early Cretaceous, Baykhangor Mongolia ; American Museum novitates, no. 3557(New York, NY : American Museum of Natural History, 2007) Turner, Alan H. (Alan Hamilton); Hwang, Sunny H.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlekh Ukhaany Akademi.A new theropod dinosaur, Shanag ashile, from the early Cretaceous Öösh deposits of Mongolia is described here. The new specimen (IGM 100/1119) comprises a well-preserved right maxilla, dentary, and partial splenial. This specimen exhibits a number of derived theropod features, including a triangular anteriorly tapering maxilla, a large antorbital fossa, and maxillary participation in the caudally elongate external nares. These features resemble the early Cretaceous dromaeosaurids Sinornithosaurus millenii and Microraptor zhaoianus, as well as the basal avialan Archaeopteryx lithographica. A comprehensive phylogenetic analysis including 58 theropod taxa unambiguously depicts the new Öösh theropod as a member of Dromaeosauridae. Relative to other dromaeosaurids, Shanag ashile is autapomorphic in its lack of a promaxillary fenestra and in the presence of interalveolar pneumatic cavities. The discovery of IGM 100/1119 expands our knowledge of early Cretaceous dromaeosaurids and the faunal similarity between the Öösh and the Jehol biotas.