Browsing by Author "Erickson, Gregory M."
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Item The osteology of Balaur bondoc, an island-dwelling dromaeosaurid (Dinosauria, Theropoda) from the late Cretaceous of Romania. (Bulletin of the American Museum of Natural History, no. 374)(American Museum of Natural History., 2013-02-13) Brusatte, Stephen.; Vremir, Mátyás.; Csiki-Sava, Zoltán.; Turner, Alan H. (Alan Hamilton); Watanabe, Akinobu, 1987-; Erickson, Gregory M.; Norell, Mark.The Hațeg Island fauna of the terminal late Cretaceous (ca. 71-65 million years ago) of Romania is one of the most unusual dinosaur assemblages in the global fossil record. It has long been recognized that many herbivorous dinosaurs from the Hațeg fauna were dwarfed, morphologically aberrant, and/or primitive relative to mainland contemporaries, and these taxa are often considered examples of the so-called island effect: the evolutionary phenomenon by which island-dwelling species are often dwarfed and anatomically modified. Very little, however, is known about the carnivorous dinosaurs that inhabited Hațeg Island, and it is unclear whether they were also dwarfed, aberrant, or primitive. In 2009, the discovery of the first substantially complete theropod from the late Cretaceous of Europe, the holotype of the Romanian dromaeosaurid Balaur bondoc, provided the first clear glimpse at an island-dwelling carnivorous dinosaur. Here we describe and figure this remarkably preserved skeleton in detail. We provide detailed descriptions and photographs of individual bones, and make extensive comparisons with other dromaeosaurids (and other derived coelurosaurian theropods). This monographic description provides further evidence that Balaur is an unusual derived dromaeosaurid, closely related to Velociraptor, with a remarkably modified hand and foot skeleton, including a stocky and heavily fused distal hind limb, a double set of hyperextensible pedal claws, and a fused and atrophied hand, which are otherwise unknown among derived coelurosaurian theropods. We present an updated diagnosis of Balaur based on additional preparation of the holotype, comparisons with other dromaeosaurids, and careful consideration of postmortem crushing. Histological techniques demonstrate that both the holotype and a referred specimen of Balaur, which is approximately 50% larger than the holotype and from a separate locality, belong to mature individuals. Therefore, we remove the referred specimen from Balaur bondoc and conservatively consider it Balaur sp. We present an updated assessment of the phylogenetic relationships of Balaur based on a comprehensive new coelurosaurian cladistics dataset, which corroborates the close relationship between Balaur, Velociraptor, Deinonychus, Adasaurus, and Saurornitholestes. We review the fossil record of European late Cretaceous theropods and show that other specimens from the late Cretaceous of Romania (including the holotype of Elopteryx), France, and Hungary either do not belong to Balaur (due to the lack of Balaur autapomorphies) or cannot be compared to Balaur because of a lack of overlapping material. Finally, we discuss the biogeographic history of European terminal Cretaceous dinosaur faunas and comment on the extreme morphological specializations of Balaur. We conclude that the phylogenetic position of Balaur, a derived dromaeosaurid closely related to late Cretaceous Laurasian taxa, is inconsistent with previous hypotheses of long-term geographic endemicity of the Romanian island faunas, but argue that the aberrant Bauplan of Balaur is similar to that seen in some living and recently extinct mammals and thus likely due to the "island effect."Item Psittacosaurus amitabha, a new species of ceratopsian dinosaur from the Ondai Sayr locality, central Mongolia. (American Museum novitates, no. 3932)(American Museum of Natural History., 2019-07-25) Napoli, James G.; Hunt, Tyler.; Erickson, Gregory M.; Norell, Mark.Psittacosaurus is the most speciose nonavian dinosaur genus, represented by at least 10 (and possibly as many as 19) species uncovered over a wide geographic range. Here, we report a new species of large-bodied Psittacosaurus from the Ondai Sayr locality in central Mongolia, which has hitherto produced only one other Psittacosaurus specimen. This new species is characterized by: (1) an elongate snout, with a gently inclined rostronasal margin, (2) a cranium dorsally convex rather than flat, (3) a subtemporal length less than 40% of total skull length, (4) a maxillary lamina that cups the posterior toothrow, (5) five premaxillary foramina arrayed in an arc, (6) an antorbital fossa as long as it is wide, and (7) a palpebral with a well-developed posterior tonguelike process. Psittacosaurus amitabha is resolved as the most basal member of the genus Psittacosaurus in our phylogenetic analysis. This taxon expands our knowledge of the already-speciose genus Psittacosaurus as well as our understanding of the Ondai Sayr fauna, which is poorly known in comparison to other Mongolian Early Cretaceous localities.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 'Psittacosaurus amitabha, a new species of ceratopsian dinosaur from the Ondai Sayr locality, central Mongolia. (American Museum novitates, no. 3932)'(2019-07-25) Napoli, James G.; Hunt, Tyler; Erickson, Gregory M.; Norell, Mark A.Supplemental Material for 'Psittacosaurus amitabha, a new species of ceratopsian dinosaur from the Ondai Sayr locality, central Mongolia. (American Museum novitates, no. 3932)'