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 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 / 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)

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 late 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.

Invertebrates

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]

Theropods

Birds

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.
Novavis[12]	N. pubisculata[12]	Changma Basin		Partial skeleton including tail vertebrae, a pelvis, and the hindlimbs.[12]	An enantiornithean.
Qiliania[13]	Q. graffini[13]	Changma Basin		"Partial skeleton from two individuals."[13]	An enantiornithean.
Unnamed enantiornithean	Indeterminate			"Partial forelimb."[14]	An enantiornithean.
Yumenornis[9]	Y. huangi[9]	Changma Basin		"Right forelimb."[9]	An euornithian.

Ornithomimosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Beishanlong[15]	B. grandis[15]	Yujingzi Basin	Gray-variegated beds	"Fore and hindlimbs with partial vertebrae."[15]	An ornithomimosaur.

Therizinosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Suzhousaurus[16]	S. megatherioides[16]	Yujingzi Basin	Gray-variegated beds	"Dorsal vertebrae, ribs and partial shoulder girdle."[16]	A therizinosauroid.

Tyrannosauroids

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Xiongguanlong[17]	X. baimoensis[17]	Yujingzi Basin	Gray-variegated beds	"Skull without lower jaws, partial vertebrae, ilium and femur."[17]	A tyrannosauroid.

Cerapods

Ceratopsians

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Archaeoceratops[18]	A. yujingziensis[19]	Yujingzi Basin	Gray-variegated beds	"Caudal vertebrae and a partial hindlimb."[19]	A neoceratopsian.

Hadrosauroids

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Jintasaurus[20]	J. meniscus[20]	Yujingzi Basin	Gray-variegated beds	"Partial skull."[20]	A hadrosauroid.
Xuwulong[21]	X. yueluni[21]	Yujingzi Basin	Gray-variegated beds	"Articulated skeleton lacking limbs."[21]	A hadrosauroid.

Sauropods

Macronarians

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Qiaowanlong[22]	Q. kangxii[22]	Yujingzi Basin	Gray-variegated beds	"Cervical vertebrae and right pelvic girdle."[22]	A somphospondylan.

Other vertebrates

Turtles

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Changmachelys[23]	C. bohlini[23]	Changma Basin		"Nearly complete skeletons from four individuals."[23]	A macrobaenid.

Fish

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Shuleichthys[24]	S. brachypteryx[24]			"Complete skeleton from four individuals."[24]	An osteoglossomorph.

Plants

Genus	Species	Location	Stratigraphic member	Material	Notes	Images
Xenoxylon[25]	X. meisteri	Hongliuxia		Wood	A podocarp

See also

• Geology portal
• Paleontology portal
• Dinosaurs portal

• 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, contemporaneous fossiliferous formation of Victoria, Australia
• Elrhaz Formation, contemporaneous fossiliferous formation of Niger
• Crato Formation, contemporaneous fossil insect bearing Lagerstätte of Brazil