Anatomy of Mahakala omnogovae (Theropoda: Dromaeosauridae), Tögrögiin Shiree, Mongolia

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.Fil: Turner, Alan Hamilton. State University Of New York. Stony Brook University. Departament Of Philosophy; Estados Unidos. American Museum of Natural History; Estados UnidosFil: Pol, Diego. Museo Paleontológico Egidio Feruglio; Argentina. American Museum of Natural History; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Norell, Mark A.. American Museum of Natural History; Estados Unido

THE OSTEOLOGY OF ALIORAMUS, A GRACILE AND LONG-SNOUTED TYRANNOSAURID (DINOSAURIA: THEROPODA) FROM THE LATE CRETACEOUS OF MONGOLIA

Fig. 68: Closeup of right ilium of the holotype specimen of Alioramus altai (IGM 100/1844) in lateral view. Scale bar 5 5 cm. Abbreviations as in figure 66.Published as part of Brusatte, Stephen L., Carr, Thomas D. & Norell, Mark A., 2012, The Osteology Of Alioramus, A Gracile And Long-Snouted Tyrannosaurid (Dinosauria: Theropoda) From The Late Cretaceous Of Mongolia, pp. 1-197 in Bulletin of the American Museum of Natural History 2012 (366) on page 149, DOI: 10.1206/770.1, http://zenodo.org/record/539926

The Geology of Ukhaa Tolgod (Djadokhta Formation, Upper Cretaceous, Nemegt Basin, Mongolia)

The lithostratigrahy and sedimentology of the fossiliferous Upper Cretaceous strata exposed in the Gobi Desert of Mongolia at Ukhaa Tolgod are described and mapped on aerial photos. Topographic features are also mapped by plane table and alidade. Five lithologic and sedimentologic facies are described: E-1, distinctly cross-stratified sandstone with fine structure, interpreted to represent eolian dune deposits; E-2, vaguely bedded sandstone with cross-stratified concretionary sheets, interpreted to represent eolian dune deposits modified by diagenetic formation of slope-parallel concretionary sheets of pedogenic calcite; S, structureless sandstone lacking concretions or cross-strata, interpreted to represent sandslide deposits generated by mass wasting along the lee slopes; C, conglomerate interpreted to represent basin-margin conglomerates washed into the dune field from adjacent topographic highs; and M, mudstone and siltstone interpreted to represent interdune deposition in ephemeral ponds and lakes. Facies E-2 and S have not been reported previously. Eleven stratigraphic sections at various localities within the Ukhaa Tolgod drainage basin are documented. The exposed composite section consists of about 75 m of pale orange sandstones, greenish-brown conglomerates, and brown siltstones that are products of an arid environment. Four schematic cross sections are documented to illustrate the lateral relationships among the five facies. In the Ukhaa Tolgod area, the beds dip about 2.5u to the south, away from the nearby Gilbent Range. This structural attitude is interpreted to be related to the uplift of the Gilbent block along normal faults exposed at the base of the range. The dune-derived sandslides of Facies S contain a rich skeletal fauna of Late Cretaceous dinosaurs, mammals, and lizards. Essentially, all the skeletal remains collected at Ukhaa Tolgod come from Facies S. Facies E-1 does contain numerous, concave-up depressions in the cross-strata interpreted as vertebrate tracks. Facies E-2 contains abundant cylindrical structures interpreted as burrows. The strata at Ukhaa Tolgod are referred to the Djadokhta Formation. As seen in the Bayn Dzak Member at Bayn Dzak, facies E-1, E-2, S, and M dominate the lower part of the section at Ukhaa Tolgod, with prominent beds of Facies C exposed near the top. Accordingly, the exposures at Ukhaa Tolgod are referred to the Bayn Dzak Member of the Djadokhta Formation. Classic exposures of the Barun Goyot Formation at Khulsan differ in having units of flat-bedded sandstone intercalated with beds of Facies S near the top of the section. To date, over 1,000 vertebrate skulls and skeletons have been collected from Facies S. Most are preserved as float contained in small calcareous nodules; however, some were found in situ. Many specimens represent either fairly complete skulls or skulls with articulated or associated postcranial skeletons. Based on faunal similarities between Bayn Dzak and Ukhaa Tolgod, the fauna at Ukhaa Tolgod is interpreted to reflect a Campanian age. The rich assemblage of fossils makes Ukhaa Tolgod one of the richest Late Cretaceous vertebrate fossil localities in the world, and the fossils provide unique insights into evolutionary developments of mammals, lizards, and dinosaurs, including birds, less than 10 my before the terminal Cretaceous extinction event

Eocene avian from Mongolia

17 p. : ill., map ; 26 cm.A well-preserved nearly complete avian tarsometatarsus was collected by the 2002 expedition of the Mongolian Academy of Sciences from Upper Eocene deposits exposed at the locality of Alag Tsav in the eastern Gobi Desert (Dornogov Aimag) of Mongolia. The new specimen is identified as part of a proposed Eogruidae clade, although it is unclear whether it is appropriately the holotype of a new species within this clade or referable to a previously named species. The clade Eogruidae has, as its current contents, species named as part of the traditional families Eogruidae + Ergilornithidae, which include several taxa of completely didactylous and apparently flightless birds. Referral of the new fossil to the clade Eogruidae is on the basis of derived reduction/loss of the metatarsal II trochlea. A series of phylogenetic analyses was used to investigate the systematic position of Eogruidae (including the new fossil, IGM 100/1447), which have been proposed to be a dominant part of Eocene to Miocene Asian faunas. First, the Mayr and Clarke (2003) dataset for crown clade Aves was used to investigate placement of Eogruidae within Aves, using a more completely known eogruid, Eogrus aeola, as an exemplar taxon. Eogrus aeola was identical to the new tarsometatarsus for all scored characters. A strict consensus cladogram of three most parsimonious trees from 1000 replicate heuristic searches placed Eogrus aeola in an unresolved polytomy with Psophiidae and Gruidae (trumpeters and cranes). Given the results of this analysis, Eogruidae (including IGM 100/1447) was analyzed in the suborder Grues dataset of Livezey (1998). Eogruidae was placed as the sister taxon to an Aramidae + Gruidae clade in the strict consensus cladogram of the eight most parsimonious trees resulting from a branch and bound search. Because monophyly of the traditional order Gruiformes has been repeatedly questioned, and the outgroups used in the original Grues dataset were identified through analyses assuming monophyly, the impact of removing these assumptions was investigated. Placement was robust to both changing outgroup assumptions and to swapping in the more incompletely known IGM 100/1447 as an exemplar for Eogruidae

New avialan fossils from Mongolia

12 p. : ill., map ; 26 cm.Includes bibliographical references (p. 10-12).Small vertebrates have remained relatively poorly known from the Nemegt Formation, although it has produced abundant and well-preserved large dinosaur remains. Here we report three new avialan specimens from the late Cretaceous (Maastrichtian) of Omnogov Aimag, Mongolia. These fossils were collected from the Nemegt Formation exposed at the locality of Tsaagan Khushu in the southern Gobi Desert. All of the new finds are partial isolated bones with a limited number of preserved morphologies; however, they further understanding of dinosaur diversity in the late Cretaceous of Mongolia and, specifically, from the Nemegt Formation. The new specimens are described and evaluated in phylogenetic analyses. These analyses indicate that all three fossils are placed as part of the clade Ornithurae. Avialan diversity of the Nemegt Formation is reviewed and briefly compared with that of the underlying Djadokhta and Barun Goyot Formations. These formations have been considered to represent at least two distinct late Cretaceous environments, with the Nemegt typically interpreted as representing more humid conditions. Ornithurine and enantiornithine birds are known from the Nemegt as well as the Djadokhta and Barun Goyot Formations, although ornithurine remains are more common in the Nemegt. No avialan species known from the Djadokhta, or Barun Goyot, are also known from the Nemegt Formation and, overall, the avialan taxa from these formations do not appear more closely related to each other than to other avialans. Whether these faunal differences are best interpreted as environmental, temporal, or sampling/preservational should be further investigated

Potential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds

Uncertainties in the phylogeny of birds (Avialae) and their closest relatives have impeded deeper understanding of early theropod flight. To help address this, we produced an updated evolutionary hypothesis through an automated analysis of the Theropod Working Group (TWiG) coelurosaurian phylogenetic data matrix. Our larger, more resolved, and better-evaluated TWiG-based hypothesis supports the grouping of dromaeosaurids + troodontids (Deinonychosauria) as the sister taxon to birds (Paraves) and the recovery of Anchiornithinae as the earliest diverging birds. Although the phylogeny will continue developing, our current results provide a pertinent opportunity to evaluate what we know about early theropod flight. With our results and available data for vaned feathered pennaraptorans, we estimate the potential for powered flight among early birds and their closest relatives. We did this by using an ancestral state reconstruction analysis calculating maximum and minimum estimates of two proxies of powered flight potential—wing loading and specific lift. These results confirm powered flight potential in early birds but its rarity among the ancestors of the closest avialan relatives (select unenlagiine and microraptorine dromaeosaurids). For the first time, we find a broad range of these ancestors neared the wing loading and specific lift thresholds indicative of powered flight potential. This suggests there was greater experimentation with wing-assisted locomotion before theropod flight evolved than previously appreciated. This study adds invaluable support for multiple origins of powered flight potential in theropods (≥3 times), which we now know was from ancestors already nearing associated thresholds, and provides a framework for its further study. Video Abstract: [Figure presented] Pei et al. use an updated phylogeny of early birds and their closest relatives to reconstruct powered flight potential, showing it evolved at least three times. Many ancestors of the closest bird relatives neared thresholds of powered flight potential, suggesting broad experimentation with wing-assisted locomotion before theropod flight evolved.Fil: Pei, Rui. Institute Of Vertebrate Paleontology And Paleoanthropology Chinese Academy Of Sciences; ChinaFil: Pittman, Michael B.. The University Of Hong Kong; Hong KongFil: Goloboff, Pablo Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Dececchi, T. Alexander. Mount Marty College; Estados UnidosFil: Habib, Michael B.. Natural History Museum Of Los Angeles County; Estados UnidosFil: Kaye, Thomas G.. Foundation For Scientific Advancement; Estados UnidosFil: Larsson, Hans C. E.. Mcgill University; CanadáFil: Norell, Mark A.. American Museum of Natural History; Estados UnidosFil: Brusatte, Stephen L.. University of Edinburgh; Reino UnidoFil: Xu, Xing. Institute Of Vertebrate Paleontology And Paleoanthropology Chinese Academy Of Sciences; Chin

Lomas Las Tetas de Cabra fauna

88 p. : ill. (1 col.), maps ; 26 cm.Includes bibliographical references (p. 64-70)."Fossil mammal and other vertebrate remains from the Lomas Las Tetas de Cabra in Baja California Norte, Mexico, provide an opportunity to examine the utility of continental scale geochronologies based on land mammal faunas. Early reports proposed a late Paleocene to early Eocene age for this fauna. Recent fieldwork and considerations of cumulative fossil discoveries strongly indicate that the Baja fauna represents the Wasatchian Land Mammal Age (early Eocene) and is strikingly similar to faunas of this age from the western interior of the United States. Wasatchian-age taxa represented in the Baja assemblage include Hyracotherium, Hyopsodus, Meniscotherium (also possibly from Clarkforkian assemblages), Diacodexis, and Prolimnocyon. Also present in the fauna are excellent specimens of Wyolestes and Esteslestes, a new genus of didelphid marsupial, as well as a badly distorted skull of a pantodont. An early Eocene age assignment is supported by analysis of the marine section adjacent to the Tetas de Cabra sequence. The marine organisms are consistent with a middle Ypresian (early Eocene) age assignment. Paleomagnetic analyses of both the terrestrial and marine sections also corroborate this age assignment. These new results substantiate the validity of the Wasatchian as a discrete temporal interval that can be applied at a continental scale. The Wasatchian thus fulfills the expectations for a mammal-based chronology. Similarities, rather than differences, between the Baja assemblage and other Wasatchian-age faunas is the dominant pattern. A choice among dispersal theories for the sources of Wasatchian mammals is not clearly indicated by the faunal evidence"--P. 3

Was Dinosaurian Physiology Inherited by Birds? Reconciling Slow Growth in Archaeopteryx

Archaeopteryx is the oldest and most primitive known bird (Avialae). It is believed that the growth and energetic physiology of basalmost birds such as Archaeopteryx were inherited in their entirety from non-avialan dinosaurs. This hypothesis predicts that the long bones in these birds formed using rapidly growing, well-vascularized woven tissue typical of non-avialan dinosaurs. We report that Archaeopteryx long bones are composed of nearly avascular parallel-fibered bone. This is among the slowest growing osseous tissues and is common in ectothermic reptiles. These findings dispute the hypothesis that non-avialan dinosaur growth and physiology were inherited in totality by the first birds. Examining these findings in a phylogenetic context required intensive sampling of outgroup dinosaurs and basalmost birds. Our results demonstrate the presence of a scale-dependent maniraptoran histological continuum that Archaeopteryx and other basalmost birds follow. Growth analysis for Archaeopteryx suggests that these animals showed exponential growth rates like non-avialan dinosaurs, three times slower than living precocial birds, but still within the lowermost range for all endothermic vertebrates. The unexpected histology of Archaeopteryx and other basalmost birds is actually consistent with retention of the phylogenetically earlier paravian dinosaur condition when size is considered. The first birds were simply feathered dinosaurs with respect to growth and energetic physiology. The evolution of the novel pattern in modern forms occurred later in the group's history