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

Description

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 middle Aptian.[1][2]

Fossil content

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.

Arthropods

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]

Birds

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

Ornithomimosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Beishanlong[13]	B. grandis[13]	Yujingzi Basin	Gray-variegated beds	"Fore and hindlimbs with partial vertebrae."[13]	An ornithomimosaur.

Therizinosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Suzhousaurus[14]	S. megatherioides[14]	Yujingzi Basin	Gray-variegated beds	"Dorsal vertebrae, ribs and partial shoulder girdle."[14]	A therizinosauroid.

Tyrannosauroids

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Xiongguanlong[15]	X. baimoensis[15]	Yujingzi Basin	Gray-variegated beds	"Skull without lower jaws, partial vertebrae, ilium and femur."[15]	A tyrannosauroid.

Ceratopsians

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Archaeoceratops[16]	A. yujingziensis[17]	Yujingzi Basin	Gray-variegated beds	"Caudal vertebrae and a partial hindlimb."[17]	A neoceratopsian.

Hadrosauroids

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Jintasaurus[18]	J. meniscus[18]	Yujingzi Basin	Gray-variegated beds	"Partial skull."[18]	A hadrosauroid.
Xuwulong[19]	X. yueluni[19]	Yujingzi Basin	Gray-variegated beds	"Articulated skeleton lacking limbs."[19]	A hadrosauroid.

Macronarians

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Qiaowanlong[20]	Q. kangxii[20]	Yujingzi Basin	Gray-variegated beds	"Cervical vertebrae and right pelvic girdle."[20]	A somphospondylan.

Turtles

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Changmachelys[21]	C. bohlini[21]	Changma Basin		"Nearly complete skeletons from four individuals."[21]	A macrobaenid.

Fish

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Shuleichthys[22]	S. brachypteryx[22]			"Complete skeleton from four individuals."[22]	An osteoglossomorph.

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, 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: 1640–1643.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. doi:10.1080/02724634.2017.1396995.
3. 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
4. P. Vršanský. 2003. Umenocoleoidea - an amazing lineage of aberrant insects (Insecta, Blattaria). AMBA Projekty 7(1):1-32
5. 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
6. Y. C. Hong. 1982. Mesozoic Fossil Insects of Jiuquan Basin in Gansu Province 1-187
7. Bailleul, Alida M.; et al. (20 March 2019). "An Early Cretaceous enantiornithine (Aves) preserving an unlaid egg and probable medullary bone". Nature Communications. 10 (1275): 1275. Bibcode:2019NatCo..10.1275B. doi:10.1038/s41467-019-09259-x. PMC 6426974. PMID 30894527.
8. Wang, Y.; O'Connor, J. K.; Li, D.; You, H. (2013). "Previously Unrecognized Ornithuromorph Bird Diversity in the Early Cretaceous Changma Basin, Gansu Province, Northwestern China". PLOS ONE. 8 (10): e77693. Bibcode:2013PLoSO...877693W. doi:10.1371/journal.pone.0077693. PMC 3795672. PMID 24147058.
9. M. Wang, D. Li, J. K. O'Connor, Z. Zhou and H. You. 2015. "Second species of enantiornithine bird from the Lower Cretaceous Changma Basin, northwestern China with implications for the taxonomic diversity of the Changma avifauna". Cretaceous Research 55: 56-65
10. O’Connor, J. K., D.-Q. Li, M. C. Lamanna, M. Wang, J. D. Harris, J. Atterholt, and H.-L. You. 2015. "A new Early Cretaceous enantiornithine (Aves, Ornithothoraces) from northwestern China with elaborate tail ornamentation". Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1054035 https://www.tandfonline.com/doi/abs/10.1080/02724634.2015.1054035?journalCode=ujvp20
11. Ji, Shu-An; Atterholt, Jessie; O'Connor, Jingmai; Lamanna, Matthew; Harris, Jerry; Li, Da-Qing; You, Hai-Lu; Dodson, Peter (2011). "A new, three-dimensionally preserved enantiornithine bird (Aves: Ornithothoraces) from Gansu Province, north-western China". Zoological Journal of the Linnean Society. 162 (1): 201–219. doi:10.1111/j.1096-3642.2010.00671.x.
12. You et al. 2005 A new fossil bird from the Early Cretaceous of Gansu Province, northwestern China Historical Biology 17(1-4):7-14
13. Makovicky, Peter J.; Li, Daqing; Gao, Ke-Qin; Lewin, Matthew; Erickson, Gregory M.; Norell, Mark A. (2010). "A giant ornithomimosaur from the Early Cretaceous of China". Proceedings of the Royal Society B: Biological Sciences. 277 (1679): 191–198. doi:10.1098/rspb.2009.0236. PMC 2842665. PMID 19386658.
14. Li, D.; Peng, C.; You, H.; Lamanna, M. C.; Harris, J. D.; Lacovara, K. J.; Zhang, J. (2007). "A Large Therizinosauroid (Dinosauria: Theropoda) from the Early Cretaceous of Northwestern China". Acta Geologica Sinica (English Edition). 81 (4): 539−549. doi:10.1111/j.1755-6724.2007.tb00977.x. ISSN 1000-9515.
15. Li, Daqing; Norell, Mark A.; Gao, Ke-Qin; Smith, Nathan D.; Makovicky, Peter J. (2009). "A longirostrine tyrannosauroid from the Early Cretaceous of China". Proceedings of the Royal Society B: Biological Sciences. 277 (1679): 183–190. doi:10.1098/rspb.2009.0249. PMC 2842666. PMID 19386654.
16. Dong, Z.; Azuma, Y. (1997). "On a primitive Neoceratopsian from the early Cretaceous of China". In Dong, Z. (ed.). Sino-Japanese Silk Road dinosaur expedition. China Ocean press. pp. 68–89.
17. You, Hai-Lu; Tanque, Kyo; Dodson, Peter (2010). "A new species of Archaeoceratops (Dinosauria: Neoceratopsia) from the Early Cretaceous of the Mazongshan area, northwestern China". In Ryan, Michael J.; Chinnery-Allgeier, Brenda J.; Eberth, David A. (eds.). New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Bloomington and Indianapolis: Indiana University Press. pp. 59–67. ISBN 978-0-253-35358-0.
18. Hai-Lu You; Da-Qing Li (2009). "A new basal hadrosauriform dinosaur (Ornithischia: Iguanodontia) from the Early Cretaceous of northwestern China". Canadian Journal of Earth Sciences. 46 (12): 949–957. doi:10.1139/E09-067.
19. You Hailu, Li Daqing and Liu Weichang (2011). "A New Hadrosauriform Dinosaur from the Early Cretaceous of Gansu Province, China". Acta Geologica Sinica. 85 (1): 51–57. doi:10.1111/j.1755-6724.2011.00377.x.
20. You, Hai-Lu; Li, Da-Qing (22 November 2009). "The first well-preserved Early Cretaceous brachiosaurid dinosaur in Asia". Proceedings of the Royal Society B: Biological Sciences. 276 (1695): 4077–4082. doi:10.1098/rspb.2009.1278. PMC 2825791. PMID 19734188.
21. Brinkman, D.B.; Yuan, C.-X.; Ji, Q.; Ji, D.; You, H. (2013). "A new turtle from the Xiagou Formation (Early Cretaceous) of Changma Basin, Gansu Province, P. R. China". Palaeobiodiversity and Palaeoenvironments. 93: 367–382.
22. 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