Xiagou Formation

The Xiagou Formation is the middle strata of the Xinminpu 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. 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.

Xiagou Formation Stratigraphic range: Aptian ~125–113 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Xinminpu Group
Underlies	Zhonggou Formation
Overlies	Chijinpu Formation
Lithology
Primary	Mudstone
Other	Shale, siltstone
Location
Coordinates	39.9°N 96.8°E / 39.9; 96.8
Approximate paleocoordinates	39.1°N 97.5°E / 39.1; 97.5
Region	Gansu
Country	China
Extent	Changma Basin
Type section
Named for	Xiagou
Xiagou Formation (China)

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 middle Aptian.[1]

Fossil content

Avimaia schweitzerae with unlaid egg

Changmaornis houi

Gansus yumenensis

Jiuquanornis niui

Yumenornis huangi

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:[2]

Enantiornithes

• Avimaia schweitzerae Bailleul et al. 2019
• Dunhuangia cuii Wang et al. 2015
• Feitianius paradisi O'Connor et al. 2015
• Qiliania graffini Ji et al. 2011

Ornithuromorphs

• Changmaornis houi Wang et al. 2013
• Gansus yumenensis Hou & Liu 1984[3]
• Jiuquanornis niui Wang et al., 2013
• Yumenornis huangi Wang et al., 2013[4]

Reptiles

• Changmachelys bohlini Brinkman et al. 2013[5]
• Testudines indet.

Insects

• Blattapterix gansu Vršanský 2003
• Cretacechorista qilianshanensis Hong et al. 1989
• Eurycoleus arcuatus, E. clypeolatus, E. dimorphocellatus, E. parvus Hong 1982
• Glottocoleus lenticulata, G. stellatus Hong 1982
• Mesoblattina cretacea Hong 1982
• Mesocoleus zhonggouense Hong 1982
• Mesotricupes reticulatus Hong 1982
• Petalocupes arcus Hong 1982
• Phyllocoleus striolatus Hong 1982
• Planocoleus ensatus Hong 1982
• Pleurocoleus catenatus Hong 1982
• Spinus yumenense Hong 1982
• Tetillopsis parvula Hong 1982
• Yumenocoleus intermedius, Y. lineatus, Y. longus Hong 1982

Fish

• Shuleichthys brachypteryx Murray et al. 2010

Other fossils from the Xiagou Formation are characteristic of an Early Cretaceous lake ecology. There are fossils of abundant fish fauna, Charophyta and ostracods.

See also

• List of fossil sites (with link directory)
• Lianmuqin Formation, contemporaneous fossiliferous formation of Xinjiang, western China
• Jiufotang Formation, contemporaneous fossiliferous formation of Liaoning, northeastern China
• Eumeralla Formation, contemporaenous fossiliferous formation of Victoria, Australia
• Elrhaz Formation, contemporaenous fossiliferous formation of Niger
• Crato Formation, contemporaneous fossil insect bearing Lagerstätte of Brazil

References

1. You et al., 2006
2. Changma, Yumen at Fossilworks.org
3. Weishampel et al., 2004, pp. 553-556
4. Wang et al., 2013, p.2
5. Brinkman et al., 2013, p.369

Bibliography

• Brinkman, D.B.; C.-X. Yuan; Q. Ji; D. Ji, and H. You. 2013. A new turtle from the Xiagou Formation (Early Cretaceous) of Changma Basin, Gansu Province, P. R. China. Palaeobiodiversity and Palaeoenvironments 93. 367–382. Accessed 2019-03-23.
• Wang, Y.-M.; J. O'Connor; D.-Q. Li, and H.-L. You. 2013. Previously unrecognised ornithuromorph bird diversity in the Early Cretaceous Changma Basin, Gansu Province, northwestern China. PLoS ONE 8. 1–14. Accessed 2019-03-23.
• Weishampel, David B.; Peter Dodson, and Halszka (eds.) Osmólska. 2004. The Dinosauria, 2nd edition, 1–880. Berkeley: University of California Press. Accessed 2019-02-21.ISBN 0-520-24209-2
• You, Hai-lu; Matthew C. Lamanna; Jerald D. Harris; Luis M. Chiappe; Jingmai O'Connor; Shu-an Ji; Jun-chang Lü; Chong-xi Yuan, and Da-qing Li; Zhang, Xing; Lacovara, Kenneth J.; Dodson, Peter and Ji, Qiang. 2006. A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China. Science 312. 1640–1643. Accessed 2019-03-23.

Further reading

• "Early Cretaceous Ostracods From The Xiagou Formation In Xiagou, Gansu Province" in Acta Micropalaeontologica Sinica part 2, 2005
• Bureau of Geology and Mineral Resources of Gansu Province,Regional Geology of Gansu Province (Geological Publishing House, Beijing, 1989), pg. 692
• Y. C. Hong, D. S. Yan, and D. R. Wang. 1989. Discovery of Early Cretaceous Cretacechorista gen. nov. Insecta: Mecoptera from Jiuquan basin Gansu Province. Memoirs of Beijing Natural History Museum 44:1-9
• Y. C. Hong. 1982. Mesozoic Fossil Insects of Jiuquan Basin in Gansu Province 1-187
• L. Hou and Z. Liu. 1984. A new fossil bird from Lower Cretaceous of Gansu and early evolution of birds. Scientia Sinica, series B 27(12):1296-1301
• A. M. Murray, H. L. You, and C. Peng. 2010. A New Cretaceous Osteoglossomorph Fish from Gansu Province, China. Journal of Vertebrate Paleontology 30(2):322-332
• P. Vršanský. 2003. Umenocoleoidea - an amazing lineage of aberrant insects (Insecta, Blattaria). AMBA Projekty 7(1):1-32
• You et al. 2015 A new fossil bird from the Early Cretaceous of Gansu Province, northwestern China Historical Biology 17(1-4):7-14