A Small Derived Theropod from Öösh, Early Cretaceous, Baykhangor Mongolia

Turner, Alan H.; Hwang, Sunny H.; Norell, Mark A.; Akademi., Mongolyn Shinzhlėkh Ukhaany

doi:10.1206/0003-0082(2007)3557[1:asdtfs]2.0.co;2

Cited by 73 publications

(93 citation statements)

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“…The caudal end of the flange curves dorsolaterally to form a flat, posteromedially facing facet that articulates with the basipterygoid process of the basisphenoid. A well-developed pterygoid flange previously was scored only for Saurornithoides mongoliensis within Troodontidae (Turner et al, 2007a(Turner et al, , 2007b. A thin, ventrolaterally projecting process defines a lateral notch that accepts the pterygoid ramus of the quadrate rostral to the basipterygoid articulation.…”

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confidence: 99%

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

Bever¹,

Norell²

2009

American Museum Novitates

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The skulls of two perinate paravians from Ukhaa Tolgod, Djadoktha Formation, Mongolia, are described here. The skulls are nearly unique in their combination of ontogenetic age and preservational quality and provide us with the first look at the morphology of such important anatomical regions as the rostrum, palate, and braincase at or near the onset of postnatal development in a nonavian paravian coelurosaur. Based on a number of derived characters, the skulls are allocated to a derived position within Troodontidae that is outside the clade consisting of Saurornithoides mongoliensis, Saurornithoides junior, Troodon formosus, and probably Sinornithoides youngi. A single synapomorphy, presence of a lateral maxillary groove, supports the Ukhaa perinates as Byronosaurus. The comparative morphology of the Ukhaa perinates with adult troodontids indicates a number of significant postnatal transformations (e.g., elongation and flattening of the rostrum, increase in the number of maxillary and dentary teeth, restructuring of the occipital plate and paroccipital process). These comparisons demonstrate that many characters historically considered important for phylogenetic and taxonomic assessments of adult maniraptorans are present at a relatively early stage of ontogeny. Differences in the developmental timing of various cranial characters have important implications for interpreting the fossil record as well as for understanding the role heterochrony has played in the evolution of derived coleurosaurs, including birds. The ontogenetic information provided by the Ukhaa perinates also allow us to comment on the enigmatic paravian Archaeornithoides deinosauriscus, which has been considered both the sister taxon to Avialae and a juvenile specimen of the troodontids Saurornithoides mongoliensis and Byronosaurus jaffei. We found no unique characters that support a priviledged relationship of Archaeornithoides deinosauriscus with avialans and only weak character support for this taxon as a basal troodontid-there is no known character evidence supporting it as a juvenile of either Saurornithoides or Byronosaurus.

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confidence: 99%

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

Bever¹,

Norell²

2009

American Museum Novitates

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“…Surprisingly, there appears to have been little evolution in body size in the Microraptorinae during their long history. The discovery of Hesperonychus indicates that microraptorines continued to exploit the small predator niche for at least 50 million years, whereas the Eudromaeosauria continued to exploit the medium-and large-bodied predator niche over the same span of time (27). In this respect, the evolution of the Dromaeosauridae appears to have been surprisingly conservative.…”

Section: Discussionmentioning

confidence: 99%

“…That dinosaurs might have left the small-carnivore niche vacant in North America is still more perplexing when one considers that many small carnivorous dinosaurs are known from Europe, Asia, and Gondwana (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). This raises the question of whether small-bodied, endothermic carnivores were truly rare in these assemblages, or whether our picture of these ecosystems is incomplete.…”

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A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America

Longrich

Currie

2009

Proc. Natl. Acad. Sci. U.S.A.

105

118

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The fossil assemblages of the Late Cretaceous of North America are dominated by large-bodied dinosaur species. Associated skeletons of small dinosaurs are exceedingly rare, and small (<10 kg) carnivorous theropods have not previously been reported from these beds. Here, we describe a small dromaeosaurid from the 75-millionyear-old Dinosaur Park Formation of Alberta, Canada. Hesperonychus elizabethae gen. et sp. nov. is represented by a pelvic girdle from an animal weighing Ϸ1,900 g. Despite its size, the pubes and ilia are coossified, indicating that the animal was somatically mature. This is the smallest carnivorous, nonavian dinosaur known from North America. Phylogenetic analysis of Hesperonychus reveals that it is not closely related to previously described North American dromaeosaurids. Instead, Hesperonychus is a member of the dromaeosaurid clade Microraptorinae, a group containing the 4-winged Microraptor and the feathered Sinornithosaurus, both from the Lower Cretaceous Jehol Group of China. Hesperonychus is the youngest known member of this lineage, extending the temporal range of the clade by 45 million years, and it is the first microraptorine known from North America, providing further evidence for an affinity between the dinosaur faunas of North America and Asia. Study of fossil collections from the Dinosaur Park and Oldman formations of Alberta has revealed numerous isolated bones of small, basal dromaeosaurids, which are tentatively referred to Hesperonychus. These fossils suggest that small dromaeosaurids were a significant component of the carnivore community in this Late Cretaceous biota.Campanian ͉ Dinosaur Park Formation ͉ microraptorinae ͉ theropoda

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“…While it is true that a number of important fossils key to this debate await monographic treatment, several statements seem incongruous given that Feduccia has himself been an author on such brief reports on Chinese fossils in both of those journals (Hou et al 1995(Hou et al , 1996(Hou et al , 1999, articles that have not resulted in the detailed follow-up studies that he criticizes others for not writing. Fortunately, a number of other important specimens and/or taxa have been the focus of extensive descriptions (e.g., Chiappe et al 1999, Turner et al 2007a, Xu et al 2009a). Details and lengthy analyses have often been made freely available as online supplements (e.g., Xu et al 2009b, .100 pages of supplementary material).…”

Section: Theoretical and Methodological Misunderstandingsmentioning

confidence: 99%

“…Ever since the discovery that some paravians had long pennaceous feathers not just on the on the forelimb but also on hindlimbs, the function of these structures has been hotly debated. In some taxa (notably Microraptor zhaoianus; see Turner et al 2007a, Li et al 2012) these feathers are asymmetric and have been considered by many to be indicative of the use of the hindlimbs in volant activity (Xu et al 2003, 2009b, Alexander et al 2010. Others have disagreed, and everything from grounddwelling cursor, to biplane glider, to ''tetrapteryx'' has been proposed as models pertaining to the evolution of avian flight (Padian and Dial 2005, Chatterjee and Templin 2007, Alexander et al 2010).…”

Section: Anatomical and Evolutionary Misinterpretationsmentioning

confidence: 99%

Rhetoric vs. reality: A commentary on “Bird Origins Anew” by A. Feduccia

Smith

Chiappe

Clarke

et al. 2015

The Auk

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Birds are maniraptoran theropod dinosaurs. The evidence supporting the systematic position of Avialae as a derived clade within Dinosauria is voluminous and derived from multiple independent lines of evidence. In contrast, a paucity of selectively chosen data weakly support, at best, alternative proposals regarding the origin of birds and feathers. Opponents of the theory that birds are dinosaurs have frequently based their criticisms on unorthodox interpretations of paleontological data and misrepresentation of phylogenetic systematic methods. Moreover, arguments against the nested position of Avialae in Dinosauria have often conflated the logically distinct questions of avian origins, the evolution of flight, and the phylogenetic distribution of feathers. Motivated by a Perspectives article with numerous factual inaccuracies that recently appeared in The Auk, we provide a review of the full complement of facts pertaining to the avian origins debate and address the misplaced criticisms raised in that opinion paper. Keywords: evolution of flight, evolution of feathers, evolution of birds, Avialae, maniraptoran theropod dinosaurs, phylogenetic systematics Retórica vs. Realidad: Un comentario sobre ''Bird Origins Anew'' por A. Feduccia, Auk 130:1-12 RESUMEN Las aves son dinosaurios terópodos maniraptores. La evidencia que sustenta la posición sistemática de Avialae como un clado derivado dentro de Dinosauria es voluminosa y se deriva de múltiples líneas independientes de evidencia. En contraste, sólo escasos datos elegidos selectivamente sustentan débilmente propuestas alternativas sobre el origen de las aves y las plumas. Los opositores de la teoría de que las aves son dinosaurios frecuentemente han basado sus críticas en interpretaciones no ortodoxas de los datos paleontológicos y en la tergiversación de los métodos de la sistemática filogenética. Además, los argumentos en contra de la posición anidada de Avialae dentro de Dinosauria han confundido la distinción lógica de las preguntas sobre los orígenes de las aves, la evolución del vuelo y la distribución filogenética de las plumas. Motivados por un artículo de Perspectivas que apareció recientemente en The Auk con numerosas imprecisiones fácticas, presentamos una revisión del conjunto completo de hechos relacionados con el debate sobre el origen de la aves y abordamos las críticas equivocadas que se presentan en dicho artículo de opinión. Palabras clave: Avialae, dinosaurios terópodos maniraptores, evolución de las aves, evolución de las plumas, evolución del vuelo, sistemática filogenética Q 2015 American Ornithologists' Union.

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A Small Derived Theropod from Öösh, Early Cretaceous, Baykhangor Mongolia

Cited by 73 publications

References 2 publications

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America

Rhetoric vs. reality: A commentary on “Bird Origins Anew” by A. Feduccia

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