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21 Aug, 2019
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Tiouraren Formation

The Tiourarén Formation is a geological formation in the Agadez Region of Niger whose strata were originally thought to be Early Cretaceous. However, re-interpretation of the sediments showed that they are probably Middle or Late Jurassic (Bathonian-Oxfordian) in age. Other works suggested it reaches the Barremian. It is the uppermost unit of the Irhazer Group. Dinosaur remains & other vertebrates are among the fossils that have been recovered from the formation. Originally part of the "Argiles de l'Ihrazer", the Tiouaren Formation primarily comprises reddish to purple siltstones with occasional marls, limestones, and scarce channel sandstones.

Description

The formation comprises reddish, almost solid mudstones, which also shows grey and white streaks, probably caused by alternating oxidative and reducing environments. Stromatolites are intermittently found in calcareous layers, while indications of semi-arid to arid conditions such as desiccation cracks and caliche horizons have been reported. The formation suggests a low-energy setting with expansive floodplains, temporary shallow lake development,and calcrete horizon interchanged with swamps, with seasonal flooding from a meandering, shallow river system dominated by overbanked silt. Many sandstone channels are composed of reworked sand grain-sized pebbles of mudstone, supporting the view of a predominantly low-relief environment. This latter feature is suggested by the widespread occurrence freshwater ostracod accumulations and rarer unionid bivalve shells.

The Early Cretaceous dating for the Tiouaren Formation was based on vertebrate fossil evidence, specially Mawsoniidae coelacanths (referred without evidence to Mawsonia lavocati), while other taxa like Hybodus? sp. and Lepidotes? sp., are either dubious or have a suggested wide temporal distribution and invertebrates (conchostracans and unionid bivalves), offer limited stratigraphic value. Recent report of an ash bed and other potentially datable beds near fossil bearing horizons opens the possibility of a future age calibration.

Fossil content

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.

Bivalves

Fishes
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Adrarunio	A. deserticus	Teguidda-n-Adrar	Lower Member	Shells	A nakamuranaiadid freshwater bivalve; one of the earliest known trigonioidoids
Afrohyrioides	A. jowikolensis	20 km E of Mount Bellal Mount Iguallala	Upper Member	Shells	A unionid freshwater bivalve
Coactunio	C. iguallalensis	Mount Iguallala Mount Ebenenanoua	Upper Member	Shells	A unionid freshwater bivalve
Paraheudeana	P. soudanensis	In-Tedreft KP-35, Zinder track Reg Tamesna	All Members	Shells	A margaritiferid freshwater bivalve
Rostrunio	R. lapparenti	KP-35, Zinder track	Upper Member	Shells	A unionid freshwater bivalve
Saharella	S. tedreftensis	Reg Tamesna	Upper Member	Shells	A unionid freshwater bivalve
Tamesnella	T. amatouensis	SE of In-Afer In-Amatou 20 km E of Mount Bellal SW of Oued Tessellamane	Upper Member	Shells	A tamesnelloid freshwater epifaunal substrate bivalve
Tamesnelloides	T. lithoides	SE of In-Afer	Upper Member	Shells	A tamesnelloid freshwater epifaunal substrate bivalve
Tegulaedon	T. humei	SE of In-Afer 35 km NE of Mount Bellal	Upper Member	Shells	A margaritiferid freshwater bivalve
Tuaregunio	T. agadesensis	KP-35, Zinder track	Upper Member	Shells	A unionid freshwater bivalve
Unionelloides	U. globulosus	Teguidda-n-Tessoumt SE of In-Afer In-Amatou 35 km NE of Mount Bellal 20 km E of Mount Bellal SW of Oued Tessellamane Erg Jadal	Upper Member	Shells	A unionid freshwater bivalve
	U. (Phortunio) giganteus	10 km E of In-Abangarit	Upper Member	Shells
	U. bellalensis	35 km NE of Mount Bellal	Upper Member	Shells
Unionida	Indet A	Reg Tamesna	All Members	Shells	Indeterminate A unionid freshwater bivalves
Unionida	Indet. B	Teguidda-n-Adrar	All Members	Shells	Indeterminate A unionid freshwater bivalves

Fishes

Fishes
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Asiatoceratodus	A. tiguidensis	Irhazer Plain Tuiguidit foreland	Upper Member	Isolated tooth plates & other remains	An asiatoceratodontid lungfish
Ceratodus	C. sp.	Tuiguidit foreland	Upper Member	Tooth plates	A ceratodontid lungfish
Holostei	Indeterminate	Tuiguidit foreland	Upper Member	"scales of ganoid fishes"	Indeterminate fish remains
Hybodus?	H.? spp.	Abaka, Agadez Tadibene Irhazer Plain	Upper Member	Teeth	A hybodontiform chondrichthyan
Mawsoniidae	Indeterminate		Upper Member	Teeth, isolated scales & partially articulated remains of the caudal fin	A coelacanth, previously referred to Mawsonia
Lepidotes?	L. spp.		Upper Member	Isolated scales	A lepisosteiform bony fish

Testudinata

"Turtle Bones" where quoted in the OR description of the unit.

Turtles
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Testudinata?	Indeterminate	Irhazer Plain	Upper Member	Isolated egg	Based on the "small size, spherical shape, and small pores" was suggested it belonged to a turtle

Crocodylomorpha

"Crocodiles" where quoted in the OR description of the unit.

Crocodylomorphs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Crocodylomorpha	Indeterminate	Tuiguidit foreland Tawachi	Upper Member	Teeth, osteoderms	Indeterminate crocodylomorph remains
Goniopholididae	Gen. et sp. nov A	Irhazer Plain	Upper Member	Complete skull	The first African goniopholidids, suggesting connections with Laurasia
Goniopholididae	Gen. et sp. nov B	Irhazer Plain	Upper Member	Narrow cranium with elongated snout

Avemetarsalia

"Rare (in abundance) pterosaurs" where quoted in the OR description of the unit.

Dinosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Afrovenator	A. abakensis	Abaka, Agadez	Upper Member	UC OBA 1, partial skull and associated postcranial remains	An afrovenatorine megalosauroidean
	A? sp.	NE of Tadibene	Upper Member	TP4-12, rostral part of left maxilla
	Cf. A sp.	Tawachi	Upper Member	Premaxillae, dentaries and appendicular skeleton
Allosauridae	Indeterminate	NE of Tadibene	Upper Member	TP4-6; TP4-7, isolated teeth	Teeth referred to allosaurids or basal allosauroids
Ceratosauria	Indeterminate	NE of Tadibene	Upper Member	TP4-4, isolated teeth	An indeterminate ceratosaur
Eusauropoda	Gen. et sp. nov 1	Irhazer Plain	Lower Member	Skull and multiple articulated postcranial skeletons	A notoriously complete taxon with stocky proportions, robust skull, and short neck
Eusauropoda	Gen. et sp. nov 2	Agadez	Upper Member	Dorsal vertebrae, humerus, and femur	Differs from other local taxa on pleurocoels on posterior dorsal vertebrae and a longer humerus relative to the femur
Jobaria	J. tiguidensis	Tamerát, Agadez Fako, Agadez Tawachi	Upper Member	Skull and several skeletons	A sauropod, maybe a eusauropod; among the most abundant terrestrial vertebrates in the formation
Megalosauridae	Indeterminate	NE of Tadibene	Upper Member	TP4-5, TP4-8, TP4-10, teeth	An indeterminate megalosaur
"Rebbachisaurus"	"R." tamesnensis	Tamerát, Agadez	Upper Member	Dorsal vertebrae and scapula	An indeterminate sauropod, also reported from younger Cretaceous beds, likely representing different taxa.
Sauropoda	Indeterminate	Tuiguidit foreland Soureya buttes	Upper Member	SMNB 1695-R, articulated caudal series, partial other postcrania Undescribed isolated & disarticulated bones	Indeterminate or unnamed sauropod remains
Spinosauridae?	Indeterminate	NE of Tadibene	Upper Member	TP4-2, TP4-3 , teeth	Referred to spinosaurs, may be of ceratosaur origin instead
Spinostropheus	S. gautieri	Fako, Agadez Tawachi Tedreft	Upper Member	Remains of many individuals including cervical, dorsal, and caudal vertebra, partial left humerus, ulna, distal pubis, distal femur, incomplete tibia, fibulae, metatarsals, pedal phalangeal fragments, and manual unguals	Possibly a basal ceratosaurian, a basal abelisauroid, or a noasaurid
Thyreophora	Gen. et sp. nov	Abaka, Agadez Tawachi	Upper Member	"Associated, but disarticulated, bones, teeth, and abundant scutes from many individuals ranging in maturity from subadult to adult"	A basal thyreophoran, suggested to be related to Scutellosaurus. A relatively common taxon, with a bonebed of up to twenty individuals.
Thyreophora	Gen. et sp. nov	Abaka, Agadez Tawachi	Upper Member
Turiasauria	Gen. et sp. nov	Agadez	Upper Member	Partial articulated skeletons	Differs from Jobaria in deflected humeral head, shorter to the ulna and radius

References

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