La Colonia Formation

The La Colonia Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.^[1]

La Colonia Formation
Stratigraphic range: Campanian-Maastrichtian ~73–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N
An outcrop of the La Colonia Formation on the Somún Curá plateau that is the type locality of Chubutinectes. Photographed in 2009.
Type	Geological formation
Sub-units	Lower, Middle and Upper members
Underlies	El Buitre & Sarmiento Formations
Overlies	Cerro Barcino & Paso del Sapo Formations
Thickness	Up to 210–240 m (690–790 ft) Thinning to 17 m (56 ft) around Telsen
Lithology
Primary	Siltstone
Other	Sandstone, claystone, conglomerate
Location
Coordinates	43.0°S 67.5°W / -43.0; -67.5
Approximate paleocoordinates	45.7°S 53.8°W / -45.7; -53.8
Region	Chubut Province
Country	Argentina
Extent	Cañadón Asfalto Basin
Type section
Named for	Sierra La Colonia
La Colonia Formation (Argentina)

Originally thought to be Campanian (c.73-72 million years ago) in age or earlier, studies of underlying formations have made a Maastrichtian (72–66 million years ago) age more likely.^[2]

Description

Paleogeography of the Late Cretaceous with La Colonia Formation indicated

It is divided up into three distinct facies, the first is up to 16 metres (52 ft) thick and consists of conglomerate, the second is by far the thickest at over 100 metres (330 ft), consists of siltstone and claystone, with interbeds of claystone/shale and sandstone, the third is less than 10 metres (33 ft) thick and consists of clay, and probably represents a nearshore marine environment.^[3]

The paleoflora was known for its aquatic components, Paleoazolla and Regnellidium. However, recent paleobotanical discoveries at the Cañadón del Irupé locality have revealed the presence of a more diverse range of plants associated with these water bodies, including pteridophytes, gymnosperms, and various angiosperms. Among these are fossil leaves and fruits assignable to Nelumbonaceae.^[4]

Fossil content

Restoration of La Colonia Formation

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.

Turtles

Turtles from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Calvarichelys[5]	C. coloniensis	Norte de Cerro Bayo 2	Middle levels	Skull and lower jaw; postcranial remains	A chelid
Patagoniaemys[3]	P. gasparinae	Buitre Chico in and around Norte de Cerro Bayo 2 Cerro Bosta		"skull fragments and several postcranial elements including a nearly complete vertebral column."[6]	A meiolaniform
Yaminuechelys[7]	aff.Y. gasparinii[3]	Norte de Cerro Bayo 1 Norte de Cerro Bayo 2 Cerro Bosta		"Three specimens formed only by postcranial remains (mainly shell fragments)"
	Y. sulcipeculiaris

Fish

Fish from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Metaceratodus[8]	M. baibianorum	Norte de Cerro Bayo 1			A ceratodontid lungfish

Plesiosaurs

Plesiosaurs from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Chubutinectes[9]	C. carmeloi			Several vertebrae, ribs, partial pectoral and pelvic girdles, arm and leg bones, and gastroliths	An elasmosaurid	Kawanectes Sulcusuchus
Elasmosauridae[3]	Indeterminate	Norte de Cerro Bayo 1 Cerro Bosta		"three postcranial specimens that preserve cervical, dorsal and caudal vertebrae, ribs and gastroliths and three vertebrae without collection number"
Kawanectes[10]	K. lafquenianum			"an incomplete mandible, nine cervical vertebrae, 14 dorsal vertebrae, three sacral vertebrae and five caudal vertebrae, and almost complete left fore limb, the isolated right humerus, both femora, ilia, pubes and the right ischium"	An elasmosaurid
Sulcusuchus[3]	S. erraini	Cerro Bosta		"part of skull and mandible"	A polycotylid

Dinosaurs

Ornithischians

Ornithischians from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ankylosauria[3]	Indeterminate	Norte de Cerro Bayo 2		An osteoderm
Hadrosauroidea[3]	Indeterminate	Norte de Cerro Bayo 2		Metatarsal fragment and two vertebral fragments

Sauropods

Sauropods from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Somphospondyli[3]	Indeterminate	Norte de Cerro Bayo 2		"Two fragmentary caudal vertebrae"
Titanomachya[11]	T. gimenezi	Norte de Cerro Bayo 2		"Partial postcranial skeleton"	A titanosaur sauropod

Theropods

Theropods from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Carnotaurus	C. sastrei	Pocho Sastre		"Nearly complete skeleton and skull"[12]	An abelisaurid[13][14]	Carnotaurus Koleken
Enantiornithine[15]	Indeterminate			A distal humerus
Koleken[3][16]	K. inakayali	Norte de Cerro Bayo 1		"Quite complete and partially articulated skeleton"	An abelisaurid.
Neornithes[17]	Indeterminate			A distal ulna	Similar to Anseriformes
Theropoda[3]	Indeterminate	Norte de Cerro Bayo 2		"Metatarsal fragments of a single individual"

Mammals

Over 300 mammal specimens have been found in the La Colonia Formation.^[18]

Mammals of the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Argentodites	A. coloniensis[19]				A possible gondwanatherian or multituberculate
Coloniatherium	C. cilinskii[20]				A meridiolestidan
Ferugliotherium	F. windhauseni[19]				A possible gondwanatherian or multituberculate
Reigitherium	R. bunodontum[21]				A meridiolestidan

Snakes

Fossils of madtsoiids, and perhaps boids, have been found in the formation.^[22]

Snakes from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Alamitophis	A. argentinus[22]			Trunk vertebra	A madtsoiid snake
Eomadtsoia	E. ragei[23]				A madtsoiid Snake

See also

• List of dinosaur-bearing rock formations
• Allen Formation, Campanian to Maastrichtian fossiliferous formation of the Neuquén Basin
• Angostura Colorada Formation, Campanian to Maastrichtian fossiliferous formation of the North Patagonian Massif
• Colorado Formation, Campanian to Maastrichtian fossiliferous formation of the Colorado Basin
• Lago Colhué Huapí Formation, Campanian to Maastrichtian fossiliferous formation of the Golfo San Jorge Basin