Guanling Formation

Not to be confused with Guanling biota.

The Guanling Formation is a Middle Triassic (Anisian or Pelsonian in the regional chronostratigraphy) geologic formation in southwestern China.

Guanling Formation
Stratigraphic range: early-mid Anisian (Pelsonian) ~247–245 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Underlies	Yangliujing Formation
Overlies	Jialingjiang Formation
Lithology
Primary	Mudstone, limestone
Other	Dolomite
Location
Coordinates	25.5°N 104.9°E / 25.5; 104.9
Approximate paleocoordinates	11.7°N 94.2°E / 11.7; 94.2
Region	Guizhou & Yunnan Provinces
Country	China
Extent	Yunnan–Guizhou Plateau
Guanling Formation (China) Show map of China Guanling Formation (Guizhou) Show map of Guizhou

Geology

The formation encompasses two members. The first member is primarily calcareous mudstone and dolomite, indicative of a coastal environment. The second member is a thicker marine sequence of dark micritic limestone with some dolomite. Two distinct fossil assemblages are found in the second member. The older Luoping biota preserves abundant arthropods (including isopods,^[1] decapods,^[2] mysidaceans and thylacocephalans^[3]) along with fossils from other invertebrates and vertebrates, which are rare but well-preserved. The slightly younger Panxian fauna has a more diverse and common assortment of marine reptiles such as sauropterygians.^[4]

A tuff bed in the Luoping biota has been dated to 244.5 ± 2.2 Ma via U-Pb SHRIMP dating. The Luoping biota as a whole was deposited over a period of 340 ± 71 kyr. This estimate is justified by cyclostratigraphic evidence, as indicated by fluctuations of terrestrial proxy metals.^[5]

Fossil content

Among others, the following fossils were reported from the formation:

Ichthyopterygia

Ichthyosauria

Genus	Species	Member	Notes	Image
Barracudasauroides[6]	B. panxianensis	Upper Member[6][4]	A small mixosaurid ichthyosaur, either a member of its own genus[7] or a species of Mixosaurus.[4]
Phalarodon[8][9]	P. cf. fraasi[8]	Upper Member[4]	Known from a skull of a small mixosaurid ichthyosaur with durophagous dentition.
	P. atavus[9]	Upper Member[4]	A small mixosaurid ichthyosaur known from a complete skeleton. Might represent a member of its own genus, Contectopalatus.
Xinminosaurus[10]	X. catactes	Upper Member[4]	A medium-sized early ichthyosaur with durophagous dentition, possibly a member of Cymbospondylidae.

Sauropterygia

Placodontiformes

Genus	Species	Member	Notes	Image
Atopodentatus[11]	A. unicus	Upper Member[11]	A bizarre, likely herbivorous[12] sauropterygian with possible placodontiform affinities,[13] known from several well-preserved specimens.
Placodus[14]	P. inexpectatus	Upper Member[14][4]	A medium-sized placodontid placodont, known from a complete specimen.[14]

Saurosphargidae

Genus	Species	Member	Notes	Image
Largocephalosaurus	L. polycarpon[15]	Upper Member [15][4]	A mid-sized basal saurosphargid sauropterygian.
	L. qianensis[16]	Upper Member [16][4]	A mid-sized basal saurosphargid sauropterygian.
Sinosaurosphargis[17]	S. yunguinensis	Upper Member [17][4]	A small armoured saurosphargid sauropterygian.

• Altisolepis
• Austronaga^[18]
• Dawazisaurus
• Diandongichthys^[19]
• Diandongosaurus
• Diandongperleidus
• Dianopachysaurus
• Dianmeisaurus
• Dinocephalosaurus^[20]
• Feroxichthys
• Frodoichthys
• Gimlichthys
• Gracilicollum
• Honghesaurus
• Kyphosichthys
• Luopingcoelacanthus
• Luopingosaurus^[21]
• Luopingperleidus
• Luoxiongichthys
• Luxisaurus^[20]
• Mixosaurus
• Nothosaurus
• Panxianichthys
• Pectodens^[20]
• Platysiagum
• Pteronisculus
• Qianosuchus
• Sanchiaosaurus
• Sangiorgioichthys
• Saurichthys
• Sinosaurichthys
• Trachelosaurus
• Venusichthys
• Wumengosaurus
• Yelangichthys
• Yudaiichthys
• Yunnancoelacanthus