Browsing by Author "Barta, Daniel E."
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Item A new specimen of the ornithischian dinosaur Haya griva, cross-Gobi geologic correlation, and the age of the Zos Canyon beds. (American Museum novitates, no. 3851)(American Museum of Natural History., 2016-02-18) Norell, Mark.; Barta, Daniel E.Although Mesozoic fossils are quite common in the Gobi Desert of Central Asia, it is often difficult to correlate among different localities because of a dearth of rocks amenable to absolute dating. Specifically, correlating between the eastern Gobi Desert and more western localities has been challenging. Here we give a Santonian-Campanian age for the enigmatic Zos Canyon beds in the Nemegt basin. This is based on the occurrence of the primitive ornithopod dinosaur Haya griva at both eastern Gobi exposures of the Javkhlant Formation and the Zos Canyon locality.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 A second specimen of Citipati osmolskae associated with a nest of eggs from Ukhaa Tolgod, Omnogov Aimag, Mongolia. (American Museum novitates, no. 3899)(American Museum of Natural History., 2018-04-26) Norell, Mark.; Balanoff, Amy M.; Barta, Daniel E.; Erickson, Gregory M.;Adult dinosaurs preserved attending their nests in brooding positions are among the rarest vertebrate fossils. By far the most common occurrences are members of the dinosaur group Oviraptorosauria. The first finds of these were specimens recovered from the Djadokhta Formation at the Mongolian locality of Ukhaa Tolgod and the Chinese locality of Bayan Mandahu. Since the initial discovery of these specimens, a few more occurrences of nesting oviraptors have been found at other Asian localities. Here we report on a second nesting oviraptorid specimen (IGM 100/1004) sitting in a brooding position atop a nest of eggs from Ukhaa Tolgod, Omnogov, Mongolia. This is a large specimen of the ubiquitous Ukhaa Tolgod taxon Citipati osmolskae. It is approximately 11% larger based on humeral length than the original Ukhaa Tolgod nesting Citipati osmolskae specimen (IGM 100/979), yet eggshell structure and egg arrangement are identical. No evidence for colonial breeding of these animals has been recovered. Reexamination of another "nesting" oviraptorosaur, the holotype of Oviraptor philoceratops (AMNH FARB 6517) indicates that in addition to the numerous partial eggs associated with the original skeleton that originally led to its referral as a protoceratopsian predator, there are the remains of a tiny theropod. This hind limb can be provisionally assigned to Oviraptoridae. It is thus at least possible that some of the eggs associated with the holotype had hatched and the perinates had not left the nest.Item Supplemental Material for 'A second specimen of Citipati osmolskae associated with a nest of eggs from Ukhaa Tolgod, Omnogov Aimag, Mongolia. (American Museum novitates, no. 3899)'(2018-04-26) Norell, Mark; Balanoff, Amy M.; Barta, Daniel E.; Erickson, Gregory M.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Supplemental Material for 'A second specimen of Citipati osmolskae associated with a nest of eggs from Ukhaa Tolgod, Omnogov Aimag, Mongolia. (American Museum novitates, no. 3899)'Item Supplemental Material for 'The osteology of Haya griva (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia. (Bulletin of the American Museum of Natural History, no. 445)'(American Museum of Natural History., 2021-02-26) Barta, Daniel E.; Norell, Mark A.Supplemental Material for 'The osteology of Haya griva (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia. (Bulletin of the American Museum of Natural History, no. 445)'