The Chorrillo Formation, also named as Chorillo Formation,[1] is a Maastrichtian (Late Cretaceous Epoch, 72.1–66 million years ago) geologic formation in southern Patagonia, Argentina. The formation is more than 50 metres (160 ft) thick and underlies the Calafate Formation and rests on top of the La Irene Formation.[2][3] It constitutes a significant uppermost Cretaceous continental sedimentary sequence within the Magallanes Basin, located in Santa Cruz Province, Argentina, approximately 30 km southwest of El Calafate. Initial investigations in the 1990s laid the groundwork, with detailed paleontological studies emerging since 2019, revealing a rich biotic assemblage.[4] The formation correlates with the lower Dorotea Formation in Chile, sharing dinosaurian ecotypes, while both are clearly different from other northern Patagonian Maastrichtian units (e.g., Allen Formation, Los Alamitos Formation), which are dominated by saltasaurine sauropods and abelisaurids, suggesting potential temporal or environmental distinctions.[3][4]
Geology
The Chorrillo Formation is embedded within the foreland Magallanes Basin, shaped by Late Cretaceous Andean orogeny driven by subduction along the Pacific margin. Tectonic subsidence, coupled with sediment supply from the rising Patagonian Andes, facilitated deposition.[4] Lithologically, the unit comprises fine- to coarse-grained clastics: mudstones and siltstones dominate floodplain facies, often organic-rich and pedogenically modified; sandstones, arkosic to lithic, form channel fills with cross-bedding; and conglomerates appear as basal lags.[5] Clay mineralogy is dominated by smectite, with minor illite and kaolinite, reflecting volcanic ash alteration. Sedimentologically, it records a meandering fluvial system on a distal floodplain, featuring fining-upward channel sequences, crevasse splays, and overbank deposits.[3] High-frequency paleosol stacking indicates local hydrologic and topographic variability, while low-frequency patterns suggest avulsion-driven progradation. Regional ties extend to the Dorotea Formation in Chile, reflecting basin-wide tectonic influences.[5]
Paleoenvironment
Paleoenvironmental reconstructions indicate a temperate-warm, seasonally humid climate with mean annual temperatures of 10-18 °C and precipitation of 900–1500 mm, inferred from paleosols, clay mineralogy, and biotic indicators.[6] Depositional settings encompass low-energy fluvial floodplains with paludal and lacustrine elements, marked by poor drainage, hydromorphic paleosols (e.g., vertisols, histosols), and redoximorphic features such as mottling and iron nodules, suggesting fluctuating water tables and episodic anoxia.[5] Aquatic communities feature Nymphaeaceae, Salviniaceae, Salviniaceae, and Zygnemataceae, indicative of freshwater ponds and swamps, while terrestrial elements include conifers, ferns, and angiosperms in riparian zones.[7] Floral phytozones, derived from palynological data, comprise five assemblages across the section, exhibiting quantitative variations in taxa proportions without major turnover: lower zones are fern-dominated (e.g., Cyatheaceae), transitioning to angiosperm-rich upper zones (e.g., Proteaceae, Nothofagidites), attributed to subtle humidity fluctuations or habitat gradients relative to fluvial channels.[8] These patterns align with Maastrichtian assemblages in southern Gondwanan basins (e.g., La Anita, Lefipán Formation), reflecting angiosperm diversification and Weddellian Province expansion.[3][8]
Fossils
Dinosaur remains are among the fossils that have been recovered from the formation.
Fossils recovered from the formation are:
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Color key
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Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
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Arthropoda
Decapoda
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Astacidea[9]
|
Indeterminate
|
"Locality 4"
|
MPM 21516, three gastroliths
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Previously identified as crushing fish teeth
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Insects
Molluscs
Gastropods
Bivalves
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Color key
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Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
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| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Chlamys[4]
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"C." salamanca
|
"Locality 5"
|
Shells
|
A Pectinidae bivalve
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|
| Cubitostrea[4]
|
C. ameghinoi
|
"Locality 5"
|
Shells
|
An Ostreidae bivalve
|
|
| Gryphaeostrea[4]
|
G. callophyla
|
"Locality 5"
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Shells
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A Gryphaeidae bivalve
|
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Fishes
Amphibians
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Anura[4]
|
Indeterminate
|
"Locality 4"
|
MPM 21518, isolated tibiofibula
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|
|
| Calyptocephalella[3][4]
|
C. gayi
|
"Locality 2"
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Incomplete left maxilla, incomplete right maxilla, incomplete right ilium, proximal right radioulna, left proximal end of tibiofibula and proximal half of urostyle
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| Calyptocephalellidae[4]
|
Indeterminate
|
"Locality 4"
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MPM 21519, distal end of right humerus with eroded distal margin
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| Pipoidea[3][4]
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Indeterminate
|
"Locality 2"
|
Distal end of right humerus
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Resembles, yet is clearly different, from Xenopus.[3]
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Plesiosaurs
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Elasmosauridae[3]
|
Indeterminate
|
"Locality 5"
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Incomplete cervical centrum and the lateral half of a very fragmentary dorsal vertebra
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May belong to the Calafate Formation
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Lepidosaurs
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Color key
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Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
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Mosasaurs
| Genus
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Species
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Locality
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Material
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Notes
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Images
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| Mosasauridae[3][4]
|
Indeterminate
|
"Locality 5"
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Seven teeth
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Its presence suggest marine influences
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Rhynchocephalian
| Genus
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Species
|
Locality
|
Material
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Notes
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Images
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| Notosphenos[12]
|
N. finisterre
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"Monotreme site"
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Incomplete right maxilla preserving two completeand one partial teeth.
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A sphenodontid rhynchocephalian
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Snakes
| Genus
|
Species
|
Locality
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Material
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Notes
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Images
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| Alethinophidia[4][12]
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Indeterminate
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"Locality 4"
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MPM 21522 small vertebra
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| Anilioidea[3]
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Indeterminate
|
"Locality 2"
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MPM-PV-22847, possible mid-precloacal vertebra
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| Coniophiidae[12]
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Indeterminate
|
"Monotreme site"
|
Nearly complete mid-posterior precloacal vertebra; Incomplete posterior precloacal vertebra
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Shares several features with Coniophis.
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| Madtsoiidae[12]
|
Indeterminate
|
"Monotreme site"; "Green Valley site"
|
Incomplete mid-posterior precloacal vertebralacking most of the neural arch; Poorly preserved precloacal vertebra preserving the verteb-ral centrum
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|
|
| Rionegrophis[4]
|
R. madtsoioides
|
"Locality 2"
|
A partial vertebra.
|
A madtsoiid snake
|
|
Turtles
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Chelidae[4]
|
Indeterminate
|
"Locality 2"
|
MPM 21520, two peripheral and one costal plates
|
Largest plates suggest a maximum carapace length of 40 cm.
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|
| Hydromedusinae[3]
|
Indeterminate
|
"Locality 2, 4, 5"
|
Left peripheral 3 or 4, bridge peripheral, fragment indet; bridge peripheral, right hypoplastron, buttress, plastral fragment and ?plastral fragment
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|
|
| Meiolaniformes[3]
|
Indeterminate
|
"Locality 4"
|
Distal end of a left humerus
|
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Archosaurs
Crocodylomorphs
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Kostensuchus[13]
|
K. atrox
|
Estancia La Anita
|
Skull, jaws, incomplete postcranial skeleton
|
A large-bodied, broad-snouted peirosaurid
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Ornithischians
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Hadrosauridae[4][14]
|
Indeterminate
|
La Anita Farm
|
Two incomplete caudal centra
|
|
|
| Isasicursor[4]
|
I. santacrucensis
|
"Locality 5"
|
Multiple specimens including teeth, several vertebrae, humerus, thigh bones, shoulder blades, and limbs
|
An elasmarian ornithopod
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|
| Ornithopoda[4][14]
|
Indeterminate
|
La Anita Farm
|
Proximal end of a femur
|
A small sized ornithopod
|
|
| Parankylosauria[14]
|
Indeterminate
|
La Anita Farm
|
Five fragmentary caudal vertebrae, incomplete ribs, two incomplete humeri, and nine osteoderms
|
|
|
Sauropods
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Fusioolithus[4]
|
F. sp.
|
"Locality 2"
|
Eggshells
|
Fusioolithidae oogenus
|
|
| Lithostrotia[15]
|
Indeterminate
|
Río Leona
|
MACN 5205 (3 middle–posterior caudal centra)
|
|
|
| Nullotitan[4]
|
N. glaciaris
|
Estancia Alta Vista; "Locality 1, 2, 4, 5"
|
A partial skeleton consisting of a third cervical vertebra, tail vertebrae, a neck rib, ribs, a left shoulder blade, the ends of a right thigh bone, a right shin, a right calf bone, and a right ankle bone
|
A colossosaurian titanosaur
|
|
| Titanosauria[4]
|
Indeterminate
|
"Locality 2, 4"
|
Seven isolated teeth[4]
|
|
|
Theropods
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Enantiornithes[3]
|
Indeterminate
|
"Locality 2, 4"
|
Distal fragment of a pedal phalanx; Two isolated ungual pedal phalanges
|
|
|
| Kookne[4]
|
K. yeutensis
|
"Locality 2"
|
An incomplete right coracoid, lacking the sternal end and the proximal end damaged
|
An ornithuran bird similar to Anseriformes
|
| Maip[16]
|
M. macrothorax
|
La Anita Farm
|
Axis, several dorsal and caudal vertebrae, cervical and dorsal ribs, gastralia, a left coracoid, fragmentary scapula, partial right pubis, and partial metatarsal
|
The largest megaraptorid theropod of South America and possibly the largest member of this group
|
| Megaraptoridae[4]
|
Indeterminate
|
La Anita Farm
|
Isolated teeth[4]
|
|
| Noasauridae[4]
|
Indeterminate
|
"Locality 4"
|
Isolated right pedal phalanx IV-2?[4]
|
Similar to Velocisaurus and Vespersaurus
|
| Prismatoolithidae[4]
|
Indeterminate
|
"Locality 4"
|
Eggshells
|
Theropod eggshells
|
| Unenlagiidae[4]
|
Indeterminate
|
"Locality 4"
|
An isolated dorsal vertebra, pedal ungual of digit II and phalanx III-2[4]
|
Similar to Neuquenraptor
|
| Yatenavis[17]
|
Y. ieujensis
|
Estancia La Anita
|
Distal right humerus
|
An enantiornithine bird
|
Mammals
| Genus
|
Species
|
Locality
|
Material
|
Notes
|
Images
|
| Magallanodon[18]
|
M. baikashkenke[19]
|
Río de Las Chinas Valley and La Anita Farm
|
Tentative first upper molariform, anterior end of a left dentary bearing part of its gliriform incisor, and upper mesial incisor from the right side
|
A ferugliotheriid gondwanathere
|
|
| M. terrwerr[20]
|
"Locality 2"
|
MPM-PV-23088, isolated right lower molariform; MPM-PV-23089, isolated right lower molariform
|
A ferugliotheriid gondwanathere
|
|
| Mammalia[4]
|
Indeterminate
|
"Locality 4"
|
Two isolated caudal vertebrae
|
Characters shared with mammals having long and gracile tails.
|
|
| Meridiolestida[20]
|
Indeterminate
|
"Monotreme site"
|
MPM-PV-21707, two fragments of a right dentary
|
Small sized taxon similar to Reigitherium.
|
|
| Mesungulatoidea[20]
|
Indeterminate
|
La Anita Farm
|
MPM-PV-21708, fragment of left dentary with five alveoli corresponding with three teeth.
|
Larger than any known Mesozoic meridiolestidan.[20]
|
|
| Orretherium[20]
|
O. tzei
|
"Monotreme site"
|
MPM-PV-23514, left upper second molariform.
|
A member of Meridiolestida belonging to the family Mesungulatidae.
|
|
| Patagorhynchus[21]
|
P. pascuali
|
"Monotreme site"
|
Lower right molar attached to a fragment of the dentary
|
A ornithorhynchid monotreme
|
|
| Patagomaia[20][22]
|
P. chainko
|
La Anita Farm
|
Partial left acetabulum and ischium; MPM-PV-23515, one fragment of thoracic vertebra, posterior half of one caudal vertebra and 38 indeterminate bones.
|
A large therian
|
|
Flora
|
|
|
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Color key
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Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
|
Algae
Liverworts
Hornworts
Lycopods
Ferns
Non-conifer Seed Plants
Conifers
Magnoliids
| Genus
|
Species
|
Affinity / Family
|
Image
|
| Clavatimonocolpites[6][8]
|
C. sp.
|
Magnoliids
|
|
Monocots
Eudicots
See also
References
- ^ Río Leona at Fossilworks.org
- ^ Marenssi et al., 2003, p.406
- ^ a b c d e f g h i j k l m n Moyano-Paz, D.; Rozadilla, S.; Agnolín, F.; Vera, E.; Coronel, M. D.; Varela, A. N.; Gómez-Dacal, A. R.; Aranciaga-Rolando, A. M.; D'Angelo, J.; Pérez-Loinaze, V.; Richiano, S.; Chimento, N.; Motta, M. J.; Sterli, J.; Manabe, M. (2022-02-01). "The uppermost Cretaceous continental deposits at the southern end of Patagonia, the Chorrillo Formation case study (Austral-Magallanes Basin): Sedimentology, fossil content and regional implications". Cretaceous Research. 130 105059. doi:10.1016/j.cretres.2021.105059. ISSN 0195-6671.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al Fernando Novas; Federico Agnolin; Sebastián Rozadilla; Alexis Aranciaga-Rolando; Federico Brissón-Eli; Matias Motta; Mauricio Cerroni; Martín Ezcurra; Agustin Martinelli; Julia D'Angelo; Gerardo Álvarez-Herrera; Adriel Gentil; Sergio Bogan; Nicolas Chimento; Jordi García-Marsà; Gastón Lo Coco; Sergio Miquel; Fatima Brito; Ezequiel Vera; Valeria Loinaze; Mariela Fernandez; Leonardo Salgado (2019). "Paleontological discoveries in the Chorrillo Formation (upper Campanian-lower Maastrichtian, Upper Cretaceous), Santa Cruz Province, Patagonia, Argentina". Revista del Museo Argentino de Ciencias Naturales. Nueva Series. 21 (2): 217–293. doi:10.22179/revmacn.21.655. hdl:11336/122229.
- ^ a b c Raigemborn, M. Sol; Lizzoli, Sabrina; Moyano-Paz, Damián; Varela, Augusto N.; Poiré, Daniel G.; Perez Loinaze, Valeria; Vera, Ezequiel; Manabe, Makoto; Novas, Fernando (2023-10-01). "Paleosols of the Maastrichtian dinosaur-bearing Chorrillo Formation (southern Patagonia, Argentina): Paleoenvironmental and paleoclimate implications". Cretaceous Research. 150 105587. doi:10.1016/j.cretres.2023.105587. ISSN 0195-6671.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca Perez Loinaze, Valeria S.; Vera, Ezequiel I.; Raigemborn, M. Sol; Moyano-Paz, Damián; Santamarina, Patricio; Agnolín, Federico; Manabe, Makoto; Tsuihiji, Takanobu; Novas, Fernando E. (2025-01-25). "Palynofloras from the Maastrichtian Chorrillo Formation (Patagonia, Argentina): Paleoenvironmental and paleoclimatic implications". Palaeogeography, Palaeoclimatology, Palaeoecology. 662 (in press) 112764. doi:10.1016/j.palaeo.2025.112764. ISSN 0031-0182.
- ^ a b c d e f g h Vera, Ezequiel I.; Perez Loinaze, Valeria S.; Moyano-Paz, Damián; Coronel, Marina D.; Manabe, Makoto; Tsuihiji, Takanobu; Novas, Fernando E. (2022-10-01). "Paleobotany of the uppermost Cretaceous Chorrillo Formation, Santa Cruz Province, Argentina: insights in a freshwater floral community". Cretaceous Research. 138 105296. doi:10.1016/j.cretres.2022.105296. ISSN 0195-6671.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc Perez Loinaze, V. S.; Vera, E. I.; Moyano-Paz, D.; Coronel, M. D.; Manabe, M.; Tsuihiji, T.; Novas, F. E. (2023). "Maastrichtian palynological assemblages from the Chorrillo Formation, Patagonia, Argentina". Review of Palaeobotany and Palynology. 314 104893. 104893. Bibcode:2023RPaPa.31404893P. doi:10.1016/j.revpalbo.2023.104893. S2CID 258043990.
- ^ Panzeri, Karen M.; Bogan, Sergio; Raigemborn, María Sol; Pagani, María Alejandra; Chimento, Nicolás; Agnolín, Federico L.; Martinelli, Agustín G. (2024-12-01). "Purported crushing teeth of actinopterygian fishes from the Late Cretaceous of Patagonia reinterpreted as crustacean bio-gastroliths". Journal of South American Earth Sciences. 149 105179. doi:10.1016/j.jsames.2024.105179. ISSN 0895-9811.
- ^ a b c d e f Vera, Ezequiel I.; Monferran, Mateo D.; Massaferro, Julieta; Sabater, Lara M.; Gallego, Oscar F.; Perez Loinaze, Valeria S.; Moyano-Paz, Damián; Agnolín, Federico L.; Manabe, Makoto; Tsuhiji, Takanobu; Novas, Fernando E. (2023-12-11). "A Maastrichtian insect assemblage from Patagonia sheds light on arthropod diversity previous to the K/Pg event". Communications Biology. 6 (1) 1249. doi:10.1038/s42003-023-05596-2. ISSN 2399-3642. PMC 10711029. PMID 38072954.
- ^ a b c d e f g h Miquel, S. E. (2024). "New species and records of freshwater and land gastropods from the Cretaceous of Argentina". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 310 (2): 119–131. doi:10.1127/njgpa/2023/1173.
- ^ a b c d Agnolín, Federico; Aranciaga Rolando, Mauro; Manabe, Makoto; Tsuihiji, Takanobu; Novas, Fernando E. (2024-05-02). "Southernmost lepidosaur (Reptilia) assemblage from the Late Cretaceous of Patagonia". Historical Biology. 37 (4): 888–902. doi:10.1080/08912963.2024.2341850. ISSN 0891-2963.
- ^ Novas, F. E.; Pol, D.; Agnolín, F. L.; Carvalho, I. S.; Manane, M.; Tsuihiji, T.; Rozadilla, S.; Lio, G. L.; Isasi, M. P. (2025). "A new large hypercarnivorous crocodyliform from the Maastrichtian of Southern Patagonia, Argentina". PLOS ONE. 20 (8) e0328561. doi:10.1371/journal.pone.0328561. PMC 12385380.
- ^ a b c Rozadilla, Sebastián; Agnolín, Federico; Manabe, Makoto; Tsuihiji, Takanobu; Novas, Fernando E. (2021). "Ornithischian remains from the Chorrillo Formation (Upper Cretaceous), southern Patagonia, Argentina, and their implications on ornithischian paleobiogeography in the Southern Hemisphere". Cretaceous Research. 125 104881. doi:10.1016/j.cretres.2021.104881. ISSN 0195-6671.
- ^ Powell, J. E. (2003). "Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects". Records of the Queen Victoria Museum. 111: 1–173.
- ^ Aranciaga Rolando AM, Motta MJ, Agnolín FL, Manabe M, Tsuihiji T, Novas FE (2022). "A large Megaraptoridae (Theropoda: Coelurosauria) from Upper Cretaceous (Maastrichtian) of Patagonia, Argentina". Scientific Reports. 12 (1) 6318. Bibcode:2022NatSR..12.6318A. doi:10.1038/s41598-022-09272-z. PMC 9042913. PMID 35474310.
- ^ Herrera, Gerardo Álvarez; Agnolín, Federico; Rozadilla, Sebastián; Lo Coco, Gastón E.; Manabe, Makoto; Tsuihiji, Takanobu; Novas, Fernando E. (2022-12-16). "New enantiornithine bird from the uppermost Cretaceous (Maastrichtian) of southern Patagonia, Argentina". Cretaceous Research. 144 105452. doi:10.1016/j.cretres.2022.105452. ISSN 0195-6671. S2CID 254804249.
- ^ Goin, Francisco J.; et al. (2020). "First Mesozoic Mammal from Chile: the southernmost RECORD of a Late Cretaceous Gondwanatherian" (PDF). Boletín del Museo Nacional de Historia Natural, Chile. 69 (1): 5–31. doi:10.54830/bmnhn.v69.n1.2020.8. S2CID 255652030.
- ^ Chimento, Nicolás R.; Agnolin, Federico L.; Tsuihiji, Takanobu; Manabe, Makoto; Novas, Fernando E. (2020-11-19). "New record of a Mesozoic gondwanatherian mammaliaform from Southern Patagonia". The Science of Nature. 107 (6). doi:10.1007/s00114-020-01705-x. ISSN 0028-1042.
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- ^ Chimento, N. R.; Agnolín, F. L.; Manabe, M.; Tsuihiji, T.; Rich, T. H.; Vickers-Rich, P.; Novas, F. E. (2023). "First monotreme from the Late Cretaceous of South America". Communications Biology. 6 (1). 146. doi:10.1038/s42003-023-04498-7. PMC 9935847. PMID 36797304.
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Bibliography