Fossil that fills a critical gap in avian evolution

Norell, Mark A.; Clarke, Julia A.

doi:10.1038/35051563

Cited by 82 publications

(71 citation statements)

References 13 publications

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“…However, its current, relatively unresolved placement best reflects the most strongly supported phylogenetic hypothesis given the data currently available. The specimen is easily differentiated from both the early Cretaceous Ambiortus dementjevi (Kurochkin, 1985) and Apsaravis ukhaana (Norell and Clarke, 2001;Clarke and Norell, 2002), the two most complete avialans known from the Mesozoic of Mongolia, by the presence of the distinct fossa excavating the posterodistal humeral head as well as by comparison of nearly every other morphology of the proximal humerus.…”

Section: Discussionmentioning

confidence: 99%

New Avialan Remains and a Review of the Known Avifauna from the Late Cretaceous Nemegt Formation of Mongolia

Clarke¹,

Norell²

2004

American Museum Novitates

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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.

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Section: Discussionmentioning

confidence: 99%

New Avialan Remains and a Review of the Known Avifauna from the Late Cretaceous Nemegt Formation of Mongolia

Clarke¹,

Norell²

2004

American Museum Novitates

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“…Outside of North America, only a handful of archaic birds can be constrained to the last half of the Maastrichtian (9,35). Nevertheless, a wide range of archaic birds are now known from the Late Cretaceous of Asia (32,33,36,37), Europe (35,38), South America (31,39), and Madagascar (40) (SI Appendix). The lack of temporal constraint makes it difficult to be certain that these birds were part of an abrupt extinction coinciding with the K-Pg boundary, yet these fossils do emphasize that the Late Cretaceous harbored an avian fauna that differed radically from that of the Cenozoic.…”

Section: Discussionmentioning

confidence: 99%

Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary

Longrich

Tokaryk

Field

2011

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

194

174

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The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous–Tertiary, K–T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K–Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K–Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis -like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs.

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“…This locality has yielded an unmatched abundance of wellpreserved vertebrate fossils, including the highest concentration of mammalian skulls and skeletons from any known Mesozoic site. More than 100 skeletons of theropod, ankylosaurian, and protoceratopsian dinosaurs have been identified, including specimens of Late Cretaceous birds (Chiappe et al, 1998(Chiappe et al, , 2002Schweitzer et al, 1999;Norell and Clarke, 2001;Suzuki et al, 2001), oviraptorid dinosaurs , including a specimen positioned on top of a nest of eggs in brooding posture Clark et al, 1999), a partial ornithomimid braincase (Makovicky and Norell, 1998) and the first known embryo of a theropod (Norell et al, 1994). Johnston et al (1996) discussed alleged vertebrate eggs that they identified as fossilized pupal chambers.…”

Section: Introductionmentioning

confidence: 99%

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

Dingus¹,

Loope²,

Dashzėvėg³

et al. 2008

Am Museum Novitates

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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.

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Fossil that fills a critical gap in avian evolution

Cited by 82 publications

References 13 publications

New Avialan Remains and a Review of the Known Avifauna from the Late Cretaceous Nemegt Formation of Mongolia

New Avialan Remains and a Review of the Known Avifauna from the Late Cretaceous Nemegt Formation of Mongolia

Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary

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

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