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Xiagou Formation

The Xiagou Formation is the middle strata of the Xinminbao Group. It is named for its type site in Xiagou, in the Changma Basin of Gansu Province, northwestern China and is considered Early Cretaceous in age. It is known outside the specialized world of Chinese geology as the site of a Lagerstätte in which the fossils were preserved of Gansus yumenensis, the earliest true modern bird.

Xiagou Formation
Stratigraphic range: late Aptian
~123–113 Ma
TypeGeological formation
Unit ofXinminbao Group
UnderliesZhonggou Formation
OverliesChijinpu Formation
Lithology
PrimaryMudstone
OtherShale, siltstone
Location
Coordinates39°54′N 96°48′E / 39.9°N 96.8°E / 39.9; 96.8
Approximate paleocoordinates39°06′N 97°30′E / 39.1°N 97.5°E / 39.1; 97.5
RegionGansu
Country China
ExtentChangma Basin
Type section
Named forXiagou
Xiagou Formation is located in China
Xiagou Formation
Xiagou Formation (China)

Description

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The laminated yellowish mudstones of the Xiagou Formation are the lithified remnants of varves that were laid down as extremely fine silt settled to the bottom of a tranquil freshwater lake. The result was dense anoxic bottom sediment, where the lack of bacteria slowed the processes of decay, preserving uncompressed fossils in details that include feather impressions and remnants of the webbing between the bird's toes. The age of the formation has not yet been confidently determined. The underlying Chijinpu Formation is likely the same age as the Jehol Group due to the presence of similar fossils, meaning that the Xiagou Formation is probably slightly younger than the Jehol biota, dating to around the late Aptian.[1][2]

Fossil content

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The Xiagou Formation is particularly noted for its high diversity of ancient birds. These include both modern birds close to the ancestors of living species, and related lineages now entirely extinct. Other fossils from the Xiagou Formation are characteristic of an Early Cretaceous lake ecology. There are fossils of abundant fish fauna, Charophyta and ostracods.[3]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Invertebrates

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Arthropods

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Genus Species Location Stratigraphic position Material Notes Images
Blattapterix[4] B. gansu[4]
Cretacechorista[5] C. qilianshanensis[5]
Eurycoleus[6] E. arcuatus, E. clypeolatus, E. dimorphocellatus, E. parvus[6] A carabid.
Glottocoleus[6] G. lenticulata, G. stellatus[6]
Mesoblattina[6] M. cretacea[6]
Mesocoleus[6] M. zhonggouense[6]
Mesotricupes[6] M. reticulatus[6]
Petalocupes[6] P. arcus[6]
Phyllocoleus[6] P. striolatus[6]
Planocoleus[6] P. ensatus[6]
Pleurocoleus[6] P. catenatus[6]
Spinus[6] S. yumenense[6]
Tetillopsis[6] T. parvula[6]
Yumenocoleus[6] Y. intermedius, Y. lineatus, Y. longus[6]

Theropods

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Birds

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Genus Species Location Stratigraphic position Material Notes Images
Avimaia[7] A. schweitzerae[7] Changma Basin "Partial skeleton with an egg."[7] An enantiornithean.
 
Brevidentavis[8] B. zhangi[8] Incomplete skull and cervical vertebrae.[8] An ornithuromorph.
Changmaornis[9] C. houi[9] Changma Basin "Partial pelvic girdle with hindlimb."[9] An euornithian.
Dunhuangia[10] D. cuii[10] Changma Basin "Forelimbs."[10] An enantiornithean.
Feitianius[11] F. paradisi[11] Changma Basin "Hindlimbs with pelvic area and vertebrae."[11] An enantiornithean.
 
Gansus[3] G. yumenensis[3] "Partial hindlimbs."[3] An euornithian.
 
Jiuquanornis[9] J. niui[9] Changma Basin "Partial pectoral girdle."[9] An euornithian.
Meemannavis[8] M. ductrix[8] Incomplete skull and cervical and thoracic vertebrae.[8] An ornithuromorph.
Qiliania[12] Q. graffini[12] Changma Basin "Partial skeleton from two individuals."[12] An enantiornithean.
Unnamed enantiornithean Indeterminate "Partial forelimb."[13] An enantiornithean.
Yumenornis[9] Y. huangi[9] Changma Basin "Right forelimb."[9] An euornithian.

Ornithomimosaurs

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Genus Species Location Stratigraphic position Material Notes Images
Beishanlong[14] B. grandis[14] Yujingzi Basin Gray-variegated beds "Fore and hindlimbs with partial vertebrae."[14] An ornithomimosaur.
 

Therizinosaurs

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Genus Species Location Stratigraphic position Material Notes Images
Suzhousaurus[15] S. megatherioides[15] Yujingzi Basin Gray-variegated beds "Dorsal vertebrae, ribs and partial shoulder girdle."[15] A therizinosauroid.
 

Tyrannosauroids

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Genus Species Location Stratigraphic position Material Notes Images
Xiongguanlong[16] X. baimoensis[16] Yujingzi Basin Gray-variegated beds "Skull without lower jaws, partial vertebrae, ilium and femur."[16] A tyrannosauroid.
 

Cerapods

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Ceratopsians

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Genus Species Location Stratigraphic position Material Notes Images
Archaeoceratops[17] A. yujingziensis[18] Yujingzi Basin Gray-variegated beds "Caudal vertebrae and a partial hindlimb."[18] A neoceratopsian.
 

Hadrosauroids

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Genus Species Location Stratigraphic position Material Notes Images
Jintasaurus[19] J. meniscus[19] Yujingzi Basin Gray-variegated beds "Partial skull."[19] A hadrosauroid.
Xuwulong[20] X. yueluni[20] Yujingzi Basin Gray-variegated beds "Articulated skeleton lacking limbs."[20] A hadrosauroid.
 

Sauropods

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Macronarians

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Genus Species Location Stratigraphic position Material Notes Images
Qiaowanlong[21] Q. kangxii[21] Yujingzi Basin Gray-variegated beds "Cervical vertebrae and right pelvic girdle."[21] A somphospondylan.
 

Other vertebrates

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Turtles

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Genus Species Location Stratigraphic position Material Notes Images
Changmachelys[22] C. bohlini[22] Changma Basin "Nearly complete skeletons from four individuals."[22] A macrobaenid.

Fish

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Genus Species Location Stratigraphic position Material Notes Images
Shuleichthys[23] S. brachypteryx[23] "Complete skeleton from four individuals."[23] An osteoglossomorph.

See also

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References

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  1. ^ You, Hai-lu; Lamanna, Matthew C.; Harris, Jerald D.; Chiappe, Luis M.; O'Connor, Jingmai; Ji, Shu-an; Lü, Jun-chang; Yuan, Chong-xi; Li; Zhang, Xing; Lacovara, Kenneth J.; Dodson, Peter and Ji, Qiang, Da-qing (2006). "A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China". Science. 312 (5780): 1640–1643. Bibcode:2006Sci...312.1640Y. doi:10.1126/science.1126377. PMID 16778053. S2CID 42723583.1640-1643&rft.date=2006&rft_id=info:doi/10.1126/science.1126377&rft_id=https://api.semanticscholar.org/CorpusID:42723583#id-name=S2CID&rft_id=info:pmid/16778053&rft_id=info:bibcode/2006Sci...312.1640Y&rft.aulast=You&rft.aufirst=Hai-lu&rft.au=Lamanna, Matthew C.&rft.au=Harris, Jerald D.&rft.au=Chiappe, Luis M.&rft.au=O'Connor, Jingmai&rft.au=Ji, Shu-an&rft.au=Lü, Jun-chang&rft.au=Yuan, Chong-xi&rft.au=Li; Zhang, Xing; Lacovara, Kenneth J.; Dodson, Peter and Ji, Qiang, Da-qing&rft_id=https://www.researchgate.net/publication/7005790&rfr_id=info:sid/en.wikipedia.org:Xiagou Formation" class="Z3988">{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ You, H.; Morschhauser, E. M.; Li, D.; Dodson, P. (2018). "Introducing the Mazongshan Dinosaur Fauna". Journal of Vertebrate Paleontology. 38 (sup. 1): 1−11. Bibcode:2018JVPal..38S...1Y. doi:10.1080/02724634.2017.1396995. S2CID 202867591.
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