Browsing by Author "Norell, Mark."
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ItemAnatomy and relationships of Gilmoreosaurus mongoliensis (Dinosauria, Hadrosauroidea) from the late Cretaceous of Central Asia. (American Museum novitates, no. 3694)(American Museum of Natural History., 2010) Prieto-Márquez, Albert, 1974-; Norell, Mark.The osteology of the hadrosauroid dinosaur Gilmoreosaurus mongoliensis is redescribed in detail based on the disarticulated cranial and postcranial elements of at least four individuals. These together constitute the lectotype and hypodigm of this species. The diagnosis is emended to include two autapomorphies (paddle-shaped postacetabular process that is less than 70% of the length of the iliac central plate and manual phalanx III-1 with greatly asymmetrical distal surface) and the unique combination of two iliac characters (presence of ischial tuberosity and supraacetabular process with apex located posterodorsal to ischial peduncle). The distinction of G. mongoliensis from B. johnsoni is confirmed on the basis of characters of the maxilla, dentition, ilium, ischium, and pubis. Maximum parsimony analysis places G. mongoliensis as a closely related outgroup to the Hadrosauridae, the sister taxon to the clade composed of all hadrosauroids closer to Telmatosaurus transsylvanicus than to Bactrosaurus johnsoni. ItemThe anatomy of Dryptosaurus aquilunguis (Dinosauria, Theropoda) and a review of its tyrannosauroid affinities. (American Museum novitates, no. 3717)(American Museum of Natural History., 2011) Brusatte, Stephen.; Benson, Roger B. J.; Norell, Mark.Although among the first theropod dinosaurs known to science, and an iconic taxon in the history of dinosaur paleontology, the large carnivore Dryptosaurus aquilunguis from the late Cretaceous of New Jersey remains poorly understood. Its anatomy has been described only in brief and its phylogenetic relationships have long been the subject of debate, although recent work proposes Dryptosaurus as a member of the tyrannosauroid clade. Here we present a thorough osteological description of the holotype of Dryptosaurus aquilunguis, supplemented with photographs of all the material, and provide extensive comparisons with other theropods, especially tyrannosauroids. In concert with recent phylogenetic analyses, our description confirms the tyrannosauroid affinities of Dryptosaurus and supports its placement as an "intermediate" taxon bracketed between small, basal forms (e.g., Guanlong, Dilong) and the derived, late Cretaceous tyrannosaurids (e.g., Albertosaurus, Tyrannosaurus). We identify several autapomorphies of Dryptosaurus, including the combination of a reduced humerus and an enlarged hand. These forelimb proportions, which differ from the uniformly large arms of basal tyrannosauroids and uniformly atrophied arms of tyrannosaurids, suggest that forelimb reduction in tyrannosauroids may not have proceeded in a uniform fashion. Functionally, Dryptosaurus may have used both its skull and arms as weapons for prey acquisition and processing. 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. ItemThe braincases of two glyptosaurines (Anguidae, Squamata) and anguid phylogeny ; American Museum novitates, no. 3613(New York, NY : American Museum of Natural History, 2008) Conrad, Jack L.; Norell, Mark.Glyptosaurines are an extinct clade of anguids whose remains are common in many Holarctic Paleogene and Cretaceous deposits. Despite their extensive fossil record (comprised mainly of scutes) the braincase is poorly known. Here, we describe braincase morphology in two North American Eocene glyptosaurines, Melanosaurus maximus and Helodermoides tuberculatus. Although generally conservative in their braincase morphology compared with other anguids, these taxa and some other "higher" glyptosaurines possess a dorsally displaced parasphenoid rostrum. The anterior openings for the Vidian canals open almost directly ventral to the parasphenoid rostrum, and the internal carotids exit anteriorly almost directly dorsal to it. Our phylogenetic analysis recovers a monophyletic Glyptosaurinae nested within Anguidae as the sister taxon to a clade containing Gerrhonotinae and Anguinae. According to our analysis, "melanosaurins" are paraphyletic, Placosaurus is paraphyletic, and Anniella is the sister taxon to Anguis. ItemA catalog of Zalmoxes (Dinosauria, Ornithopoda) specimens from the Upper Cretaceous Nălaț-Vad locality, Hațeg Basin, Romania. (American Museum novitates, no. 3884)(American Museum of Natural History., 2017-10-23) Brusatte, Stephen.; Dumbravă, Mihai.; Vremir, Mátyás.; Csiki-Sava, Zoltán.; Totoianu, Radu.; Norell, Mark.The Transylvanian area of Romania boasts a rich fossil record of dinosaurs, which lived on an island (Haţeg Island) during the very end of the Cretaceous. Many of these are dwarfed in body size or exhibit other unusual features thought to be linked to their insular habitat. One of the most common of these dinosaurs is the rhabdodontid ornithopod Zalmoxes, an herbivorous taxon that has been found at many Upper Cretaceous sites across Transylvania. Our collaborative fieldwork has uncovered several new Zalmoxes specimens from the Nălaț-Vad (= Vadu) locality, a site along the Râul Mare River in the Hațeg Basin that dates to the "middle" to late Maastrichtian. These include a partial associated skeleton, along with various isolated bones from several additional individuals. We catalog and describe these specimens here, and compare them to other Zalmoxes fossils from Romania. They provide further evidence that Zalmoxes was one of the most common vertebrates in the latest Cretaceous of Transylvania, and add to the unusual fossil record of Nălaț-Vad, which has yielded a much greater number of associated skeletons than other Transylvanian localities. Some of the Nălaț-Vad specimens possess features characteristic of the type species, Z. robustus, whereas others exhibit features diagnostic of the larger and stockier Z. shqiperorum, indicating that these species were locally sympatric, as has been demonstrated at other Transylvanian sites. The specimens span much of the size range known from Zalmoxes, as well as the spatial and temporal extent of the Nălaț-Vad locality, suggesting that this taxon flourished until near the end of the Cretaceous. 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). ItemComplex overlapping joints between facial bones allowing limited anterior sliding movements of the snout in diplodocid sauropods. (American Museum novitates, no. 3911)(American Museum of Natural History., 2018-10-25) Tschopp, Emanuel; Mateus, Octávio; Norell, Mark.Diplodocid sauropods had a unique skull morphology, with posteriorly retracted nares, an elongated snout, and anteriorly restricted, peglike teeth. Because of the lack of extant analogs in skull structure and tooth morphology, understanding their feeding strategy and diet has been difficult. Furthermore, the general rarity of sauropod skulls and the fragility of their facial elements resulted in a restricted knowledge of cranial anatomy, in particular regarding the internal surface of the facial skull. Here, we describe in detail a well-preserved diplodocid skull visible in medial view. Diagnostic features recognized in other skulls observable in lateral view, such as the extended contribution of the jugal to the antorbital fenestra, are obliterated in medial view due to extensive overlapping joints between the maxilla, jugal, quadratojugal, and the lacrimal. These overlapping joints permitted limited anterior sliding movement of the snout, which likely served as a kind of "shock-absorbing" mechanism during feeding. Diplodocid skulls therefore seem to have evolved to alleviate stresses inflicted on the snout during backward movements of the head, as would be expected during branch-stripping or raking. 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 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. ItemCranial 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. ItemCranial 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. ItemThe cranial pneumatic sinuses of the tyrannosaurid Alioramus (Dinosauria, Theropoda) and the evolution of cranial pneumaticity in theropod dinosaurs. (American Museum novitates, no. 3790)(American Museum of Natural History., 2013-12-05) Leone Gold, Maria Eugenia.; Brusatte, Stephen.; Norell, Mark.Archosaurs and mammals exhibit skeletal pneumaticity, where bone is infilled by air-filled soft tissues. Some theropod dinosaurs possess extensively pneumatic skulls in which many of the individual bones are hollowed out by diverticula of three main cranial sinus systems: the paranasal, suborbital, and tympanic sinuses. Computed tomography (CT scanning) permits detailed study of the internal morphology of cranial sinuses. But only a few theropod specimens have yet been subjected to this type of analysis. We present CT scans of the remarkably preserved and disarticulated skull bones of the long-snouted tyrannosaurid theropod Alioramus. These scans indicate that Alioramus has extensive cranial pneumaticity, with pneumatic sinuses invading the maxilla, lacrimal, jugal, squamosal, quadrate, palatine, ectopterygoid, and surangular. Pneumaticity is not present, however, in the nasal, postorbital, quadratojugal, pterygoid, or angular. Comparisons between Alioramus and other theropods (most importantly the closely related Tyrannosaurus) show that the cranial sinuses of Alioramus are modified to fill the long-snouted skull of this taxon, and that Alioramus has an extreme degree of cranial pneumaticity compared to other theropods, which may be the result of the juvenile status of the specimen, a difference in feeding style between Alioramus and other theropods, or passive processes. Based on these comparisons, we provide a revised terminology of cranial pneumatic structures and review the distribution, variation, and evolution of cranial pneumaticity within theropod dinosaurs. This review illustrates that most theropods possess a common "groundplan" in which the maxilla and lacrimal are pneumatized, and that various theropods modify this groundplan by pneumatizing numerous other bones of the skull. Tyrannosaurids are very pneumatic compared to other theropods, particularly in the development of extensive ectopterygoid, quadrate, and palatine sinuses, as well as a pneumatic invasion into the surangular. Tyrannosauroids seem to retain many cranial sinuses, such as the jugal and nasal recesses, which are primitive for coelurosaurs but lost or apomorphically modified in taxa more closely related to birds. ItemThe earliest iguanine lizard (Reptilia, Squamata) and its bearing on iguanine phylogeny. American Museum novitates ; no. 2997(New York, N.Y. : American Museum of Natural History, 1991) Norell, Mark.; De Queiroz, Kevin. ItemThe Early Cretaceous crocodylomorph Hylaeochampsa vectiana from the wealden of the Isle of Wight. American Museum novitates ; no. 3032(New York, N.Y. : American Museum of Natural History, 1992) Clark, James Matthew, 1956-; Norell, Mark. ItemAn early ostrich dinosaur and implications for ornithomimosaur phylogeny. American Museum novitates ; no. 3420(New York, NY : American Museum of Natural History, 2003) Ji, Qiang.; Norell, Mark.; Makovicky, Peter J.; Gao, Keqin, 1955-; Ji, Shu'an.; Yuan, Chongxi.A new ornithomimosaur from the Yixian Formation of Liaoning Province Peoples Republic of China is described. These beds are near the Jurassic-Cretaceous boundary. This specimen is interesting because it has several primitive characters for ornithomimosaurs such as teeth and a short first metacarpal. This taxon is placed in a phylogenetic analysis of Coelurosauria and shown to be near the base of the ornithomimosaur clade. Using this phylogeny we comment on the biogeographic history of this group. 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. ItemErketu 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. 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.