The Ituzaingó Formation (Spanish: Formación Ituzaingó), in older literature also described as Entre Ríos or Entrerriana Formation, is an extensive geological formation of Late Miocene (Tortonian, or Huayquerian in the SALMA classification) age in the Paraná Basin of the Corrientes, Santa Fe and Entre Ríos Provinces in Mesopotamia, northeastern Argentina. The formation comprises mudstones, cross-bedded sandstones and conglomerates deposited in a fluvio-deltaic environment and is renowned for the preservation of a rich fossil assemblage, including many mammals, birds, reptiles, fish, bivalves, foraminifera, ichnofossils and flora.

The Ituzaingó Formation was first described by De Alba in 1953 and later by Herbst in 1971. The up to 150 metres (490 ft), but in most areas between 10 and 20 metres (33 and 66 ft) thick formation is found in an area of 120,000 square kilometres (46,000 sq mi), stretching from the Paraná River to 40 kilometres (25 mi) east of Tostado. The Ituzaingó Formation crops out in the northeasternmost part of Argentina (Mesopotamia), in the provinces of Corrientes, Santa Fe and Entre Ríos, among other locations along the banks of the Paraná River.

The formation overlies the marine Paraná Formation and is unconformably overlain by the Puerto Alvear, Hernandarías and Yupoí Formations of Early Pleistocene (Uquian and Ensenadan respectively) age. At the shores of the Paraná River, the formation underlies the Timbúes Formation. In certain places along the same river, the formation cuts into the underlying Rosario Formation.

The formation contains a basal conglomeratic member "Conglomerado osífero" (bony conglomerate) with abundant vertebrate remains. This conglomerate is overlain by almost unfossiliferous whitish to yellow brown sandstones and green mudstones. The Ituzaingó Formation (as Entre Ríos Formation) was correlated with the Puelches Formation of the subsurface of Buenos Aires Province. According to the mammals occurring in the conglomerate and the stratigraphic relationships, the age of the base of Ituzaingo Formation is almost exclusively Tortonian (Late Miocene) or Huayquerian in the SALMA classification.

The formation, as the Paraná and Puelches Formations, has been deposited in a vast Miocene tidal flat environment. Both the terrestrial and freshwater fauna of the Ituzaingó Formation indicates a climate warmer than present. The freshwater vertebrate record suggests important basin connections with Amazonian basins.

Alternatively, the Conglomerado Osífero Member has been interpreted as tide-dominated fluvial channels, pertaining to the marine Paraná Formation.

The Ituzaingó Formation has provided a large variety of fossils, of various groups, from mammals to birds and reptiles to fish and flora. The terrestrial fauna is predominant while a few marine genera are also present. The presence of typical Amazonian freshwater fish and absence of austral fauna in both the underlying Paraná and the Ituzaingó Formation suggests a connection with northern areas of South America. The faunas has been correlated to the older Miocene faunas of the Honda Group at La Venta in Colombia, the Urumaco Formation at Urumaco in Venezuela and the Pebas Formation of the Amazon region of Colombia, Ecuador, Peru and Brazil. Several ground sloth genera present in the Ituzaingó Formation are endemic from this unit, whereas other are also present in the Arroyo Chasicó Formation of Buenos Aires Province, the Andalhuala and Corral Quemado Formations of Catamarca Province, and the Toro Negro Formation of La Rioja Province.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Andalgalornis	A. steulleti
Devincenzia	D. pozzi
Macranhinga	M. paranensis
	M. ranzii
Palaelodus	P. cf. ambiguus
Rhea	R. (Pterocnemia) mesopotamica
Megapaloelodus	M. sp.
Phoenicopteridae	Indeterminate.
Phorusrhacidae	Indetermidate.
Rallidae	Indeterminate.
Rheidae	Indeterminate.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Eumysops	E. parodii
Notictis	N. ortizi

Taxa	Species	Presence	Abundance	Description	Images	Notes
Saurocetes	S. gigas
Iniidae indet.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Brachytherium	B. cuspidatum
Cullinia	C. sp.
Diadiaphorus	D. paranensis
Neobrachytherium	N. ameghinoi
Oxyodontherium	O. piramydatus
	O. zeballosi
Paranauchenia	P. denticulata
Promacrauchenia	P. antiqua
Proterotherium	P. cervioides
Scalabrinitherium	S. bravardi
	S. rothii

Taxa	Species	Presence	Abundance	Description	Images	Notes
Philander	P. entrerianus
Chironectes	C. sp.
Zygolestes	Z. paranensis

Taxa	Species	Presence	Abundance	Description	Images	Notes
Thylacosmilus	T. atrox
Stylocynus	S. paranensis

Taxa	Species	Presence	Abundance	Description	Images	Notes
Briaromys	B. trouessartianus
Cardiatherium	C. paranense
Carlesia	C. pendolai
Diaphoromys	D. compressidens
	D. gamayensis
	D. mesopotamicus
Doellomys	D. parcus
Eumegamys	E. contortus
	E. dubius
	E. scalabrinianus
	E. paranensis
Eumegamysops	E. praependens
Gyriabrus	G. glutinatus
	G. holmbergi
	G. indivisus
	G. rebagliattii
Haplostropha	H. sacabriniana
Isostylomys	I. ameghinoi
	I. laurillardi
Lagostomopsis	L. antiquus
	L. pallidens
Myocastor	M. obesus
	M. paranensis
	M. sinuata
Neoepiblema	N. ambrosettianus
	N. horridula
Olenopsis	O. typicus
Paradoxomys	P. cancrivorus
Pentastylodon	P. racedi
Pentastylomys	P. seriei
Perimys	P. scalabrinianus
Phoberomys	P. burmeisteri
	P. insolita
	P. lozanoi
	P. minima
	P. praecursor
Phugatherium	P. cataclisticum
Potamarchus	P. murinus
	P. sigmodon
Protabrocoma	P. paranensis
Protomegamys	P. coligatus
Pseudosigmomys	P. paranensis
Rusconia	R. crassidens
Strophostephanos	S. jheringi
Telodontomys	T. compressidens
Tetrastylomys	T. castellanosi
Tetrastylus	T. aguilari
	T. diffusus
	T. laevigatus
	T. robustus
	T. (Protelicomys) atavus
Anatochoerus
Anchimysops	A. sp.
Cardiatherium
Cardiomys
Caviodon
Colpostemma sp.
Contracavia
Kiyutherium
Paleocavia
Parodimys
Plexochoerus
Pliodolichotis
Procardiatherium
Prodolichotis
Protohydrochoerus

Taxa	Species	Presence	Abundance	Description	Images	Notes
Adinotherium	?A. paranense
?Berroia	?B. sp.
Dilobodon	D. lutarius
Dinotoxodon	D. paranensis
Eutomodus	E. elautus
Haplodontherium	H. limun
Palaeotoxodon	P. paranensis
	?P. protoburmeisteri
	?P. virgatus
Stenotephanos	S. plicidens
Toxodontherium	T.compressum
	T. reverendum
Xotodon	X. doellojuradi
	X. foricurvatus

Taxa	Species	Presence	Abundance	Description	Images	Notes
Munyizia	M. paranensis
Protypotherium	P. antiquum
Trachytypotherium	T. sp.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Berthawyleria	B. sp.
Chasicotatus	C. spinozai
Chlamyphractus	C. pressulus
Comaphorus	C. concisus			A dubious glyptodont.
Dasypus	D. neogarus			Relatives of nine-banded armadillos.
Eleutherocercus	E. paranensis			A glyptodont.
Kraglievichia	K. paranense
Macroeuphractus	M. retusus
Palaehoplophorus	P. antiquus
Paraglyptodon	P. paranensis
Parahoplophorus	P. paranensis
Plohophorus	P. paranensis
Proeuphractus	P. limpidus
Protoglyptodon	P. primiformis
Pseudoeuryurus	P. lelongianus
Scirrotherium	S. carinatum
Trachycalyptus	?T. cingulatus
Urotherium	U. interundatum
Zaedyus	?Z. sp.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Amphiocnus	A. paranense
Eomegatherium	E. nanum
Megabradys	M. darwini
Megalonychops	M. primigenius
Mesopotamocnus	M. brevirostrum
Neohapalops	N. rothi
Octomylodon	O. aversus
Ortotherium	O. laticurvatum
	O. robustum
	O. schlosseri
	O. scrofum
	O. seneum
Paranabradys	P. vucetichae
Pliomegatherium	P. lelongi
Pliomorphus	P. ameghinoi
	P. gracilis
	P. mutilatus
	P. robustus
Prolestodon	P. antiquus
	P. paranensis
Promegatherium	P. parvulum
	P. smaltatum
Promylodon	P. paranensis
Pronothrotherium	P. mirabilis
Protomegalonyx	P. doellojuradoi
	P. praecursor
Pyramiodontherium	P. sp.
Ranculcus	R. scalabrinianus
Scelidotheriidae	Indeterminate.
Sphenotherus	S. paranensis
Strabosodon	S. acuticavus
	S. obtusicavus
Torcellia	T. paranense

Taxa	Species	Presence	Abundance	Description	Images	Notes
Cyonasua	C. Argentina

Taxa	Species	Presence	Abundance	Description	Images	Notes
Caiman	C. australis			Relative of Caiman
	C. cf. yacare
	C. latriostris
	C. yacare
Gryposuchus	G. neogaeus			A giant extinct gavialid crocodilian.
Mourasuchus	M. arendsi
Paranacaiman	P. bravardi
Paranasuchus	P. gasparinae
Tupinambis	T. cf. merianae
Parahydraspis	P. paranaensis
Phrynops	P. cf. geoffroanus
Testudo	T. paranensis

Taxa	Species	Presence	Abundance	Description	Images	Notes
Colossoma	C. macropomum
Megapiranha	M. paranensis
Potamotrygon	P. motoro
Squatina	S. dumeril
Phractocephalus	P. ivy
Cynodontidae	Indetermidate.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Protelphidium	P. tuberculatum
Ostrea	O. sp.

Taxa	Species	Presence	Abundance	Description	Images	Notes
Anadenantheroxylon	A. villaurquicense
Astroniumxylon	A. bonplandianum
	A. parabalansae
Curtiembreoxylon	C. poledrii
Gleditsioxylon	G. paramorphoides
Guadua	G. morronei
	G. zuloagae
Laurinoxylon	L. artabeae
Mangroveoxylon	M.areniensis
Menendoxylon	M. vasallensis
Microlobiusxylon	M. paranaensis
Maytenoxylon	M. sp.
Mimosoxylon	M. sp.
Palmoxylon	P. yuqueriense
Prosopisinoxylon	P. americanum
Prumnopityoxylon	P. gnaedingerae
Ruprechtioxylon	R. breae
Scalarixylon	S. sp.
Schinopsixylon	S. heckii
Soroceaxylon	S. entrerriensis
Syagrus	S. sp.
Uruguaianoxylon	U. striata

Taxa	Species	Presence	Abundance	Description	Images	Notes
Arenicolites

Huayquerian correlations in South America

Formation	Cerro Azul	Ituzaingó	Paraná	Camacho	Raigón	Andalhuala	Chiquimil	Las Flores	Maimará	Palo	Pebas	Muyu	Rosa	Saldungaray	Salicas	Urumaco	Map
Basin	Colorado	Paraná				Hualfín		Tontal	Andes	Salta	Amazon	Huasi	Altiplano	BA	Velasco	Falcón	Ituzaingó Formation (South America)
Country	Argentina			Uruguay		Argentina					Brazil  Peru	Bolivia		Argentina		Venezuela
Cardiatherium
Lagostomus
Macroeuphractus
Proeuphractus
Pronothrotherium
Pseudotypotherium
Thylacosmilus
Xotodon
Macraucheniidae
Primates
Rodents
Reptiles
Birds
Terror birds
Flora
Environments	Aeolian-fluvial	Fluvio-deltaic			Fluvial						Fluvio-lacustrine	Fluvial			Fluvio-lacustrine	Fluvio-deltaic	Huayquerian volcanoclastics Huayquerian fauna Huayquerian flora
Volcanic						Yes

• South American land mammal ages
• Honda Group
• Pebas Formation
• Urumaco
• Battle of Ituzaingó

• El Neógeno de la Mesopotamia argentina
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