Browsing by Author "Mongolyn Shinzhlėkh Ukhaany Akademi."
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ItemAnatomy of Mahakala omnogovae (Theropoda, Dromaeosauridae), Tögrögiin Shiree, Mongolia. (American Museum novitates, no. 3722)(American Museum of Natural History., 2011-10-05) Turner, Alan H. (Alan Hamilton); Pol, Diego.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The dromaeosaurid Mahakala omnogovae is known from a unique specimen from the late Cretaceous deposits of the Djadokhta Formation at Tögrögiin Shiree, Ömnögov Aimag, Mongolia. The holotype specimen is comprised of a well-preserved but partial skull and a nearly complete postcranial skeleton. Mahakala omnogovae is included in a comprehensive phylogenetic analysis of Coelurosauria using a dataset, which reflects a greatly expanded character set and taxon-sampling regime. Several interesting features of Mahakala omnogovae have implications for deinonychosaurian and avialan character evolution and for understanding patterns of size variation and size change within paravian theropods. These morphologies include the shape of the iliac blade, the triangular obturator process of the ischium, and the evolution of the subarctometatarsalian condition. We present an expanded diagnosis of Mahakala omnogovae which included following unique combination of characters (autapomorphies noted by *): a ledgelike depression at the confluence of metotic strut and posterior tympanic recess on the anterior face of the paroccipital process*, a posteriorly tapering scapula; a shortened forelimb (humerus 50% femur length); a strongly compressed and anteroposteriorly broad ulna tapering posteriorly to a narrow edge*; elongate lateral crest on the posterodistal femur*; anterior caudal vertebrae with subhorizontal, laterally directed prezygapophyses*; a prominent supratrochanteric process; and the absence of a cuppedicus fossa. ItemThe braincase anatomy of the late Cretaceous dinosaur Alioramus (Theropoda, Tyrannosauroidea). (Bulletin of the American Museum of Natural History, no. 376)(American Museum of Natural History., 2013-03-15) Bever, Gabe S.; Brusatte, Stephen.; Carr, Thomas D. (Paleontologist); Xu, Xing, 1969-; Balanoff, Amy M.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The late Cretaceous tyrannosaurid Alioramus altai is known from a single specimen whose articulated braincase exhibits a nearly unique combination of preservational quality, subadult stage of growth, and morphological complexity. We use a detailed physical preparation combined with high-resolution computed tomography to provide an expanded description of this braincase that includes details of the neurocranium and its dermal roof, pneumatic recesses and sinuses, cranial endocast, and inner ear cavities. A few notable features include a highly developed rostral tympanic recess marked by three pneumatic fenestrae, a highly pneumatic paroccipital process with both rostral and caudal pneumatic foramina, a prootic fossa housing external foramina for the trigeminal and facial nerves, a well-developed superficial lamina of the prootic, an expanded vestibular cavity, and an osseous labyrinth that is plesiomorphic in appearance. These observations, set within the currently available comparative context, elucidate numerous neuroanatomical transformations within Tyrannosauroidea and clarify where more data and work are needed. We expand the discussion for the 21 characters from the neurocranium utilized in a recent revision of tyrannosauroid phylogeny, including a listing of which tyrannosauroid taxa can be scored for the primitive and derived states of each character. ItemBraincase and phylogenetic relationships of Estesia mongoliensis from the late Cretaceous of the Gobi Desert and the recognition of a new clade of lizards. American Museum novitates ; no.3211(New York, N.Y. : American Museum of Natural History, 1997) Norell, Mark.; Gao, Keqin, 1955-; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemA complete late Cretaceous iguanian (Squamata, Reptilia) from the Gobi and identification of a new iguanian clade ; American Museum novitates, no. 3584(New York, NY : American Museum of Natural History, 2007) Conrad, Jack L.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Iguania is a diverse clade with an incompletely known fossil record. Here, we describe and name the earliest iguanian known from a complete skeleton. The specimen (IGM 3/858) comes from Ukhaa Tolgod (Upper Cretaceous of Mongolia) and offers important insights into the evolutionary history of iguanian osteology. The new taxon is diagnosed by a combination of character states, including the presence of a frontoparietal fontanelle, absence of an enlarged nuchal fossa, and unflared tooth crowns. We performed a cladistic analysis including 54 taxa scored for 202 informative morphological characters. A strict consensus of 46 shortest recovered trees reveals that the new taxon is a basal member of a previously unidentified clade of Cretaceous iguanians, probably endemic to the Gobi. This clade of Gobi iguanians is nested within a monophyletic Pleurodonta (non-acrodontan iguanians). ItemConvergent evolution of a eusuchian-type secondary palate within Shartegosuchidae. (American Museum novitates, no. 3901)(American Museum of Natural History., 2018-06-18) Dollman, Kathleen N.; Clark, James Matthew, 1956-; Norell, Mark.; Xu, Xing, 1969-; Choiniere, Jonah N.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Shartegosuchids are a poorly known, early-branching group of Asian and North American crocodylomorphs. Shartegosuchids have been hypothesized to have eusuchian-type secondary palates, but a paucity of described material makes assessing this difficult. Our fieldwork in western Mongolia recovered cranial material of a new Shartegosuchus specimen from the Ulan Malgait Formation, which we CT-scanned and digitally reconstructed to investigate its palatal morphology. We then incorporated this new anatomical information into a revised phylogenetic dataset to assess its affinities. Our study confirms that Shartegosuchus has a posteriorly placed choana that is fully enclosed by the pterygoids, but differs from Eusuchia in possessing a secondary palatal fenestra and reduced palatine bones. Shartegosuchus, together with Adzhosuchus, Fruitachampsa, and Nominosuchus, forms the monophyletic group Shartegosuchidae. Shartegosuchidae is nested within a larger clade Shartegosuchoidea, and this clade is an earlier-diverging lineage than Eusuchia, showing that a eusuchian-type secondary palate evolved multiple times in crocodylomorphs, including very early in the group's evolutionary history. The co-occurrence of Nominosuchus in the Ulan Malgait Formation and the Shishigou Formation allows us to assign an early Oxfordian age to Shartegosuchus. The independent evolution of a eusuchian-type secondary palate in an oreinorostral group suggests that the link between platyrostry and a closed secondary palate has been overstated. ItemCranial anatomy and phylogenetic position of Tsaganomys altaicus (Mammalia, Rodentia) from the Hsanda Gol Formation (Oligocene), Mongolia. American Museum novitates ; no.3156(New York, N.Y. : American Museum of Natural History, 1995) Bryant, J. Daniel (James Daniel), 1966-; McKenna, Malcolm C.; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemCranial anatomy of Citipati osmolskae (Theropoda, Oviraptorosauria), and a reinterpretation of the holotype of Oviraptor philoceratops. American Museum novitates ; no. 3364(New York, NY : American Museum of Natural History, 2002) Clark, James Matthew, 1956-; Norell, Mark.; Rowe, Timothy, 1953-; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.; Central Asiatic Expeditions (1921-1930)We describe the skull of the holotype of Citipati osmolskae, one of the best preserved oviraptorid skulls known. The skull preserves stapes and epipterygoids, and the mandible preserves a slender coronoid bone, none of which has been reported before in oviraptorids. The braincase is similar to that of other basal coelurosaurs but possesses extensive recesses presumably occupied by pneumatic diverticulae; the circumnarial region is highly pneumatized, and a large recess continues posteriorly from the narial region to invade the frontals and parietals dorsal to the braincase. Circum-otic pneumatic recesses include two dorsal recesses above the otic recess, a posterior recess on the anterior surface of the paroccipital process, and extensive cavities in the basisphenoid beneath the braincase. The more dorsal of the two dorsal tympanic recesses is very deep, and CT scans suggest that it connected medially across the midline dorsal to the otic region and anteriorly with the frontoparietal space. The otic recess is unusually shallow. Comparison of the new skull with the poorly preserved skull of the holotype of Oviraptor philoceratops demonstrates that the braincase and palate of the latter are similar to those of other oviraptorids. Its rostrum and dentary are more elongate than in other oviraptorids, however, a more plesiomorphic condition suggesting it may be the most basal oviraptorid. A well-preserved skeleton previously referred to O. philoceratops, IGM 100/42, does not belong to this genus or species, and its narial region is very similar to that of Citipati osmolskae. ItemThe cranial anatomy of Cricetops dormitor, an Oligocene fossil rodent from Mongolia. American Museum novitates ; no. 3275(New York, NY : American Museum of Natural History, 1999) Carrasco, Marc A.; Wahlert, John H.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.; Central Asiatic Expeditions (1921-1930)"A description of the cranial, mandibular, and dental morphology of Cricetops dormitor, an Oligocene muroid rodent, is presented. Cricetops exhibits a unique combination of primitive muroid characters (e.g., the presence of a large hystricomorphous infraorbital foramen) and derived muroid characters (e.g., a prominent metacone in the upper third molar) that cloud its taxonomic affiliations. In addition, Cricetops dormitor lacks many characters, including a highly inclined zygomatic plate, that have been used to unite members of the family Muridae. Overall, these results suggest that the phylogenetic position of Cricetops within the Muroidea needs to be reevaluated"--P. . ItemCranial anatomy of Kryptobaatar dashzevegi (Mammalia, Multituberculata), and its bearing on the evolution of mammalian characters. Bulletin of the AMNH ; no. 247([New York] : American Museum of Natural History, 2000) Wible, John R.; Rougier, Guillermo W.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The cranial anatomy of the Mongolian late Cretaceous multituberculate Kryptobaatar dashzevegi is described based on exquisitely preserved specimens collected from Ukhaa Tolgod and Tugrugeen Shireh in the Gobi Desert by joint expeditions of the American Museum of Natural History and the Mongolian Academy of Sciences. Most sutural relationships are preserved, enabling a bone-by-bone description of the skull and lower jaws exclusive of the nasal fossa and paranasal sinuses. A reconstruction of the principal components of the cranial nervous, arterial, and venous systems is facilitated by specimens with exposed endocranial surfaces. Comparisons with previously described multituberculates, other Mesozoic mammaliaforms, and extant mammals allow an assessment of major topics in the evolutionary morphology of the multituberculate and mammaliaform skull, as well as identification of Kryptobaatar as an appropriate model regarding most aspects of the multituberculate skull for future phylogenetic studies. Elements previously unknown or poorly known in multituberculates are described. Included are a complete jugal on the internal surface of the zygoma; the orbital mosaic and foramina, including the optic foramen, the metoptic foramen, the transverse canal, and the foramen for the pituito-orbital vein; and the endocranium with an extensively ossified primary braincase wall formed by the pilae metoptica and antotica. The latter pila is very robust compared with its ossified remnants in non-mammalian cynodonts and monotremes, suggesting that it is a derived multituberculate condition. The co-occurrence of the pilae metoptica and antotica in multituberculates is thus far unique among mammaliaforms, but agrees with the morphology expected to be primitive for Mammalia. This in turn implies an independent loss of an ossified pila metoptica in monotremes, marsupials, and Vincelestes or the loss of the pila metoptica in the ancestry of multituberculates and therians combined with the independent reacquisition of a neomorphic pila metoptica in multituberculates and eutherians. The absence of several elements from the multituberculate skull, controversial in nature, is confirmed, including the prenasal process of the premaxilla, the septomaxilla, the ectopterygoid, and the orbital process of the palatine. Also confirmed is the presence of several controversial elements in the multituberculate skull, including an alisphenoid with a reduced contribution to the braincase and an anterior lamina expanded dorsal to the alisphenoid. Competing anatomical hypotheses for several elements are addressed, including the function of the lateral pterygopalatine trough as muscle attachment and not for the auditory tube, the homology of the postorbital process on the parietal with that on the frontal, the identity of foramina in the anterior lamina as for mandibular nerve branches and not for the mandibular and maxillary nerves, and the function of the jugular fossa as primarily having housed a diverticulum of the cavum tympani and not large cranial nerve ganglia. The cranial arterial system in Kryptobaatar generally resembled that restored for other multituberculates and for other mammaliaforms, in particular the prototribosphenidan Vincelestes. Both Kryptobaatar and Vincelestes had a transpromontorial internal carotid artery, a stapedial artery that ran through a bicrurate stapes, ramus inferior, ramus superior, and an arteria diploëtica magna. The cranial venous system in Kryptobaatar resembled that described for other Mongolian late Cretaceous multituberculates and for monotremes with the major exits of the dural sinuses having been the prootic canal and the foramen magnum. A revised diagnosis of Kryptobaatar distinguishes it from other djadochtatherians (the grouping that includes 10 of the 11 genera of Mongolian late Cretaceous multituberculates) by a pterygoid canal either confluent with or barely separated from the carotid canal and a separate hypoglossal foramen. ItemEarliest eutherian ear region : a petrosal referred to Prokennalestes from the early Cretaceous of Mongolia. American Museum novitates ; no. 3322(New York, NY : American Museum of Natural History, 2001) Wible, John R.; Rougier, Guillermo W.; Novacek, Michael J.; McKenna, Malcolm C.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.A right petrosal from the ?Aptian or Albian Khoobur locality is referred on the basis of size and morphology to Prokennalestes trofimovi, the earliest eutherian previously known only from dentigerous elements. The petrosal shows a mosaic of primitive and derived features, bearing on the purported therian and eutherian morphotypes. Among the primitive features shared with the early Cretaceous prototribosphenidan Vincelestes and other more basal taxa that are modified in later eutherians and metatherians are the pattern of basicranial arterial and venous circulation, including a prootic canal and an intrapetrosal inferior petrosal sinus; a vertical paroccipital process; and a fenestra semilunaris, an incomplete wall between the cavum epiptericum and cavum supracochleare. Among the derived features shared with therians is a cochlea coiled through a minimum of 360°, with Prokennalestes extending the range of the oldest occurrence of such a coiled cochlea by at least 10 million years. Shared with late Cretaceous eutherians is a shallow internal acoustic meatus with a thin prefacial commissure. The petrosal referred to Prokennalestes is intermediate in having a reduced anterior lamina and lateral flange, both of which are well developed in Vincelestes and essentially lacking in later eutherians and metatherians. Features previously held to be part of the therian and eutherian morphotypes, such as the absence of the anterior lamina and lateral flange, may have been lost independently in metatherians and in post-Prokennalestes eutherians. ItemAn embryonic oviraptorid (Dinosauria, Theropoda) from the Upper Cretaceous of Mongolia. American Museum novitates ; no. 3315(New York, NY : American Museum of Natural History, 2001) Norell, Mark.; Clark, James Matthew, 1956-; Chiappe, Luis M.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.An embryonic oviraptorid skeleton is described within an egg from the late Cretaceous Djadokh[t]a Formation of Ukhaa Tolgod, Mongolia. The specimen comprises the ventral part of the skull and most of the mandible, a poorly preserved axial skeleton missing most of the tail, and portions of the forelimbs, shoulder girdles, pelvis, and hindlimbs. The skull is readily referable to the theropod dinosaur clade Oviraptoridae on the basis of several skull specializations (edentulous, vertically oriented premaxilla, a sinusoidally shaped lower jaw, and an unusual articulation of the vomer and premaxilla), and the postcranial skeleton is consistent with this identification. The egg is equivalent in overall shape and microstructure to those found beneath several oviraptorid skeletons recovered from the same formation. The skeleton is well ossified and, in comparison with ossification patterns in living Aves, the evidence suggests that this species was closer to the precocial end of the precocial-altricial spectrum of developmental patterns. ItemEstesia mongoliensis : a new fossil varanoid from the late Cretaceous Barun Goyot Formation of Mongolia. American Museum novitates ; no.3045(New York, N.Y. : American Museum of Natural History, 1992) Norell, Mark.; McKenna, Malcolm C.; Novacek, Michael J.; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemThe first record of a pterosaur from the early Cretaceous strata of Oösh (Ovörkhangai, Mongolia). American Museum novitates ; no. 3472(New York, NY : American Museum of Natural History, 2005) Andres, Brian.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Although dinosaur fossils are common in the early Cretaceous strata of Oösh, remains of other vertebrates are rare. Here we describe the first pterosaur fossil known from this locality. The specimen consists of a single vertebra that exhibits sufficient morphology to identify it as a nonazhdarchid tapejaroid pterosaur. Remains of such animals have been found in similarly aged rocks (some with accompanying similar faunas) throughout Central Asia. ItemGobiconodonts from the early Cretaceous of Oshih (Ashile), Mongolia. American Museum novitates ; no. 3348(New York, NY : American Museum of Natural History, 2001) Rougier, Guillermo W.; Novacek, Michael J.; McKenna, Malcolm C.; Wible, John R.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.We describe here the first discovered mammalian remains from the Mongolian early Cretaceous locality Oshih (Ashile). Four fragmentary, tooth-bearing specimens, probably corresponding to three individuals, have been recovered. All the fossils can be assigned to the family Gobiconodontidae (Chow and Rich, 1984). The specimens include three lower jaw fragments and one upper jaw fragment, and represent at least two different taxa. Gobiconodon hopsoni, n. sp., is described and diagnosed here. This new species is larger than G. ostromi (early Cretaceous Cloverly Formation, USA); thus, it is the largest triconodont and one of the largest Mesozoic mammals known. Gobiconodon sp., found also at Oshih, is slightly larger than G. borissiaki, from the early Cretaceous of Khoobur, Mongolia, but smaller than G. ostromi. The specimens of this second species are poorly preserved and provide insufficient data for a diagnosis. The status of the different species of Gobiconodon and the new gobiconodontid Hangjinia is reviewed. In gobiconodontids and Triconodontidae, the maxillae appear to make a significant contribution to the orbital rim, a condition unusual among basal mammals, in which the lacrimal and jugal are the main components. Other triconodonts such as Jeholodens, likely an "amphilestid", appear to show the primitive mammalian condition for this feature. We present a brief consideration of triconodont relationships and discuss alternative placements of Gobiconodon among Mammaliaformes. ItemImportant features of the dromaeosaur skeleton : information from a new specimen. American Museum novitates ; no. 3215(New York, N.Y. : American Museum of Natural History, 1997) Norell, Mark.; Makovicky, Peter J.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemImportant features of the dromaeosaurid skeleton. 2, Information from newly collected specimens of Velociraptor mongoliensis. American Museum novitates ; no. 3282(New York, NY : American Museum of Natural History, 1999) Norell, Mark.; Makovicky, Peter J.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The postcranial anatomy of several new specimens of Velociraptor mongoliensis is described. This description concentrates on poorly known aspects of the skeleton of Velociraptor mongoliensis, including several features that are extremely similar to characters found in basal avialans like Archaeopteryx lithographica. Among these the pelvis and shoulder girdle display several characters such as a reduced antiliac shelf, a furcula, a scapula lying in a subhorizontal position relative to the dorsal column, and sternal plates that articulate with the coracoids. Some problematic features and conditions such as the hypopubic cup and the degree of opisthopuby are also discussed in relation to claims made about these features in regard to the origin of Avialae. Comparisons are made between Velociraptor mongoliensis and the enigmatic maniraptoran Unenlagia comahuensis"--P. . ItemA leptictid mammal from the Hsanda Gol Formation (Oligocene), Central Mongolia, with comments on some Palaeoryctidae. American Museum novitates ; no.3168(New York, N.Y. : American Museum of Natural History, 1996) Kellner, Alexander Wilhelm Armin.; McKenna, Malcolm C.; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemA mammalian petrosal from the early Cretaceous of Mongolia : implications for the evolution of the ear region and mammaliamorph interrelationships. American Museum novitates ; no.3149(New York, N.Y. : American Museum of Natural History, 1995) Wible, John R.; Rougier, Guillermo W.; Novacek, Michael J.; McKenna, Malcolm C.; Dashzėvėg, Dėmbėrėliĭn.; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemMiddle-ear ossicles of the multituberculate Kryptobaatar from the Mongolian late Cretaceous : implications for mammaliamorph relationships and the evolution of the auditory apparatus. American Museum novitates ; no. 3187(New York, N.Y. : American Museum of Natural History, 1996) Rougier, Guillermo W.; Wible, John R.; Novacek, Michael J.; Mongolyn Shinzhlėkh Ukhaany Akademi. ItemThe morphology and phylogenetic position of Apsaravis ukhaana from the late Cretaceous of Mongolia. American Museum novitates ; no. 3387(New York, NY : American Museum of Natural History, 2002) Clarke, Julia A.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The avialan taxon Apsaravis ukhaana from the late Cretaceous of southern Mongolia is completely described and its phylogenetic position is evaluated. Apsaravis ukhaana is from continental sandstones exposed at the locality of Ukhaa Tolgod, Omnogov Aimag, Mongolia. The holotype specimen consists of the nearly complete, articulated skeleton of a small volant avialan. Apsaravis ukhaana is unambiguously differentiated from other avialans based on the presence of several unique morphologies: a strong tubercle on the proximal humerus, a hypertrophied trochanteric crest on the femur, and extremely well-projected posterior wings of a surface of the distal tibiotarsus that in Aves articulates with the tibial cartilage. Ten other homoplastic characters optimize as autapomorphies of Apsaravis ukhaana in the phylogenetic analysis. They are as follows: ossified mandibular symphysis; dentary strongly forked posteriorly; hooked acromion process on scapula; highly angled dorsal condyle of humerus; humeral condyles weakly defined; distal edge of humerus angling strongly ventrally; humerus flared dorsoventrally at its distal terminus; lateral condyle of tibiotarsus wider than medial one; neither condyle of tibiotarsus tapering toward the midline; and metatarsal II trochlea rounded rather than ginglymoid. Phylogenetic placement of Apsaravis ukhaana as the sister taxon of Hesperornithes + Aves resulted from analysis of 202 characters scored for 17 avialan ingroup taxa. The implications of Apsaravis ukhaana, and the results of the phylogenetic analysis, for the evolution of flight after its origin and character support for enantiornithine monophyly are extensively discussed.