Browsing by Author "Xu, Xing, 1969-"
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Item The 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.Item Convergent 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.Item Cranial osteology of Haplocheirus sollers Choiniere et al., 2010 (Theropoda, Alvarezsauroidea). (American Museum novitates, no. 3816)(American Museum of Natural History., 2014-10-22) Choiniere, Jonah N.; Clark, James Matthew, 1956-; Norell, Mark.; Xu, Xing, 1969-The basalmost alvarezsauroid Haplocheirus sollers is known from a single specimen collected in Upper Jurassic (Oxfordian) beds of the Shishugou Formation in northwestern China. Haplocheirus provides important data about the plesiomorphic morphology of the theropod group Alvarezsauroidea, whose derived members possess numerous skeletal autapomorphies. We present here a detailed description of the cranial anatomy of Haplocheirus. These data are important for understanding cranial evolution in Alvarezsauroidea because other basal members of the clade lack cranial material entirely and because derived parvicursorine alvarezsauroids have cranial features shared exclusively with members of Avialae that have been interpreted as synapomorphies in some analyses. We discuss the implications of this anatomy for cranial evolution within Alvarezsauroidea and at the base of Maniraptora.Item Cranial osteology of the theropod dinosaur Incisivosaurus gauthieri (Theropoda, Oviraptorosauria). (American Museum novitates, no. 3651)(2009) Balanoff, Amy M.; Xu, Xing, 1969-; Kobayashi, Yoshimura.; Matsufune, Yusuke.; Norell, Mark.We provide a description of the holotype skull of the unusual oviraptorosaur Incisivosaurus gauthieri. Previous phylogenetic analyses have placed this taxon firmly within Oviraptorosauria near the base of the clade; however, until now only a cursory description of this important specimen was available. The presence of many primitive characteristics (e.g., maxillary and dentary teeth as well as an extended palate and rostrum) indicates that the observed similarities between avians and derived oviraptorids are convergences rather than shared derived characters. In addition, we clarify previous descriptions of several ambiguous anatomical features, most notably of the palate. We also employ computed tomographic (CT) analysis, which allows for a more complete description of the braincase and the reconstruction of an endocranial endocast. CT imagery reveals features that were before unobtainable, such as the presence of a replacement tooth behind the large rodentiform incisor in the premaxilla. This arrangement indicates that although the incisiform teeth of I. gauthieri are morphologically distinct they are replaced in typical archosaurian fashion.Item Osteology of a new late Cretaceous troodontid specimen from Ukhaa Tolgod, Ömnögovi Aimag, Mongolia. (American Museum novitates, no. 3889)(American Museum of Natural History., 2017-12-15) Pei, Rui.; Norell, Mark.; Barta, Daniel E.; Bever, Gabe S.; Pittman, Michael, 1985-; Xu, Xing, 1969-A new troodontid dinosaur, Almas ukhaa, from the Late Cretaceous deposits of the Djadokhta Formation at Ukhaa Tolgod, Mongolia, is described here. The holotype specimen (IGM 100/1323) comprises an almost complete and articulated cranium and partial articulated postcranial skeleton. This specimen has a small body size and a short snout as in basal paravians, but it exhibits a number of derived troodontid features that differentiate Almas ukhaa from the Early Cretaceous troodontids reported from China and unite this new taxon with other Late Cretaceous troodontids. Relative to other troodontids, Almas ukhaa is autapomorphic in the presence of a posteriorly curved pterygoid flange, absence of a lateral groove on the anterior part of the dentary, presence of a distinct spikelike process on the ischium, and elongate chevrons. The eggshell associated with IGM 100/1323 can be assigned to Prismatoolithidae indet. based on the smooth surface, eggshell thickness, and microstructural characteristics, and also preserves attributes similar to Protoceratopsidovum minimum. A unique relationship between Byronosaurus and the perinate troodontids IGM 100/972 and IGM 100/974 is no longer supported based on the new observations of Almas ukhaa and Gobivenator.Item Pennaraptoran theropod dinosaurs : past progress and new frontiers. (Bulletin of the American Museum of Natural History, no. 440)(American Museum of Natural History., 2020-08-21) Pittman, Michael, 1985-; Xu, Xing, 1969-; O'Connor, Jingmai.; Field, Daniel J.; Turner, Alan H. (Alan Hamilton); Ma, Waisum.; Makovicky, Peter J.; Tse, Edison.; Norell, Mark.; Pei, Rui.; Pol, Diego.; Goloboff, Pablo A.; Ding, Anyang.; Upchurch, Paul.; Berv, Jacob S.; Hsiang, Allison Y.; Landis, Michael J.; Dornburg, Alex.; Nebreda, Sergio M.; Navalón, Guillermo.; Menéndez, Iris.; Sigurdsen, Trond.; Chiappe, Luis M.; Marugán-Lobón, Jesús.; Wang, Shuo.; Stiegler, Josef.; Wu, Ping.; Zhong, Zhengming.; Lautenschlager, Stephan.; Meade, Luke E.; Roy, Arindam.; Rogers, Christopher S.; Clements, Thomas.; Habimana, Olivier.; Martin, Peter.; Heers, Ashley M.; Serrano, Francisco J.; Habib, Michael B.; Dececchi, T. Alexander.; Kaye, Thomas G.; Larsson, Hans C.E.; Wang, Xiaoli.; Zheng, Xiaoting.; Novas, Fernando E.; Agnolín, Federico L.; Egli, Federico Brisson.; Lo Coco, Gastón E.Introduction / Michael Pittman and Xing Xu -- Section 1. Systematics, fossil record, and biogeography -- Chapter 1. Pennaraptoran systematics / Michael Pittman, Jingmai O’Connor, Daniel J. Field, Alan H. Turner, Waisum Ma, Peter Makovicky, and Xing Xu -- Chapter 2. The fossil record of Mesozoic and Paleocene pennaraptorans / Michael Pittman, Jingmai O’Connor, Edison Tse, Peter Makovicky, Daniel J. Field, Waisum Ma, Alan H. Turner, Mark A. Norell, Rui Pei, and Xing Xu -- Chapter 3. The impact of unstable taxa in coelurosaurian phylogeny and resampling support measures for parsimony analyses / Diego Pol and Pablo A. Goloboff -- Chapter 4. The biogeography of coelurosaurian theropods and its impact on their evolutionary history / Anyang Ding, Michael Pittman, Paul Upchurch, Jingmai O’Connor, Daniel J. Field, and Xing Xu -- Chapter 5. Timing the extant avian radiation : the rise of modern birds, and the importance of modeling molecular rate variation / Daniel J. Field, Jacob S. Berv, Allison Y. Hsiang, Robert Lanfear, Michael J. Landis, and Alex Dornburg -- Section 2. Anatomical frontiers -- Chapter 6. Disparity and macroevolutionary transformation of the maniraptoran manus / Sergio M. Nebreda, Guillermo Navalón, Iris Menéndez, Trond Sigurdsen, Luis M. Chiappe, and Jesús Marugán-Lobón -- Chapter 7. Tooth vs. beak : the evolutionary developmental control of the avian feeding apparatus / Shuo Wang, Josef Stiegler, Ping Wu, and Cheng-ming Chuong -- Chapter 8. Functional morphology of the oviraptorosaurian and scansoriopterygid skull / Waisum Ma, Michael Pittman, Stephan Lautenschlager, Luke E. Meade, and Xing Xu -- Chapter 9. Fossil microbodies are melanosomes : evaluating and rejecting the ‘fossilised decay-associated microbes’ hypothesis / Arindam Roy, Christopher S. Rogers, Thomas Clements, Michael Pittman, Olivier Habimana, Peter Martin, and Jakob Vinther -- Section 3. Early-flight study : methods, status, and frontiers -- Chapter 10. Methods of studying early theropod flight / Michael Pittman, Ashley M. Heers, Francisco J. Serrano, Daniel J. Field, Michael B. Habib, T. Alexander Dececchi, Thomas G. Kaye, and Hans C.E. Larsson -- Chapter 11. High flyer or high fashion? A comparison of flight potential among small-bodied paravians / T. Alexander Dececchi, Hans C.E. Larsson, Michael Pittman, and Michael B. Habib -- Chapter 12. Navigating functional landscapes : a bird’s eye view of the evolution of avialan flight / Hans C.E. Larsson, Michael B. Habib, and T. Alexander Dececchi -- Chapter 13. Laser-stimulated fluorescence refines flight modeling of the Early Cretaceous bird Sapeornis / Francisco J. Serrano, Michael Pittman, Thomas G. Kaye, Xiaoli Wang, Xiaoting Zheng, and Luis M. Chiappe -- Chapter 14. Pectoral girdle morphology in early-diverging paravians and living ratites : implications for the origin of flight / Fernando E. Novas, Federico L. Agnolín, Federico Brisson Egli, and Gastón E. Lo Coco.Item Supplemental Material for 'Pennaraptoran theropod dinosaurs : past progress and new frontiers. (Bulletin of the American Museum of Natural History, no. 440)'(American Museum of Natural History., 2020-08-21) Pittman, Michael, 1985-; Xu, Xing, 1969-; O'Connor, Jingmai.; Field, Daniel J.; Turner, Alan H. (Alan Hamilton); Ma, Waisum.; Makovicky, Peter J.; Tse, Edison.; Norell, Mark.; Pei, Rui.; Pol, Diego.; Goloboff, Pablo A.; Ding, Anyang.; Upchurch, Paul.; Berv, Jacob S.; Hsiang, Allison Y.; Landis, Michael J.; Dornburg, Alex.; Nebreda, Sergio M.; Navalón, Guillermo.; Menéndez, Iris.; Sigurdsen, Trond; Chiappe, Luis M.; Marugán-Lobón, Jesús.; Wang, Shuo.; Stiegler, Josef.; Wu, Ping.; Zhong, Zhengming.; Lautenschlager, Stephan.; Meade, Luke E.; Roy, Arindam.; Rogers, Christopher S.; Clements, Thomas.; Habimana, Olivier.; Martin, Peter.; Heers, Ashley M.; Serrano, Francisco J.; Habib, Michael B.; Dececchi, T. Alexander.; Kaye, Thomas G.; Larsson, Hans C.E.; Wang, Xiaoli.; Zheng, Xiaoting.; Novas, Fernando E.; Agnolín, Federico L.; Egli, Federico Brisson.; Lo Coco, Gastón E.Supplemental Material for 'Pennaraptoran theropod dinosaurs : past progress and new frontiers. (Bulletin of the American Museum of Natural History, no. 440)'