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.Weishampel et al., 2004, pp.600-604
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.Rauhut, 2003 A further study in 2021 utilizing magnetostratigraphy and palynological data provided an age of 69 to 64 million years ago.
Description
It is divided up into three distinct facies, the first is up to thick and consists of conglomerate, the second is by far the thickest at over , consists of siltstone and claystone, with interbeds of claystone/shale and sandstone, the third is less than thick and consists of clay, and probably represents a nearshore marine environment.
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.
During the Maastrichtian, Patagonia was flooded by the Transgression of the Kawas Sea. This would have likely rendered much of Patagonia, including the region represented by what is now the La Colonia Formation, scattered faunal Islands.
Fossil content
Turtles Turtles from the La Colonia Formation Genus Species Location Stratigraphic position Material Notes Images Calvarichelys C. coloniensis Norte de Cerro Bayo 2 Middle levels Skull and lower jaw; postcranial remains A chelid Patagoniaemys 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 columnSterli & De la Fuente, 2011 A meiolaniform Yaminuechelys aff.Y. gasparinii Norte de Cerro Bayo 1 Norte de Cerro Bayo 2 Cerro BostaThree specimens restricted to postcranial remains (mainly shell fragments) Y. sulcipeculiaris
Fish Fish from the La Colonia Formation Genus Species Location Stratigraphic position Material Notes ImagesMetaceratodusM. baibianorumNorte de Cerro Bayo 1 A ceratodontid lungfish
Plesiosaurs Plesiosaurs from the La Colonia Formation Genus Species Location Stratigraphic position Material Notes ImagesChubutinectesC. carmeloiSeveral vertebrae, ribs, partial pectoral and pelvic girdles, arm and leg bones, and gastrolithsAn elasmosaurid Elasmosauridae indet. Indeterminate Norte de Cerro Bayo 1 Cerro Bosta Three postcranial specimens that preserve cervical, dorsal, and caudal vertebrae, ribs, gastroliths, and three vertebrae without collection numbers. KawanectesO'Gorman, 2019 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 S. erraini Cerro Bosta Part of the skull and mandible A polycotylid
Dinosaurs Ornithischians Ornithischians from the La Colonia Formation Genus Species Location Stratigraphic position Material Notes Images Ankylosauria indet. Indeterminate Norte de Cerro Bayo 2 An osteoderm Unnamed ParankylosauriaUnnamedMultiple specimens including cranial and postcranial remains, representing much of the complete skeletonAn unnamed and undescribed parankylosaur with a 'cudgel-like' tail weapon distinct from that of Stegouros Hadrosauroidea indet. Indeterminate Norte de Cerro Bayo 2 Metatarsal fragment and two vertebral fragments Unnamed HadrosauridaeUnnamedAn articulated skeleton with a complete skullAn unnamed and undescribed hadrosaurid related to other South American kritosaurins, representing the most complete hadrosaur from the continent
Sauropods Sauropods from the La Colonia Formation Genus Species Location Stratigraphic position Material Notes Images Somphospondyli indet. Indeterminate Norte de Cerro Bayo 2 "Two fragmentary caudal vertebrae" Titanomachya T. gimenezi Norte de Cerro Bayo 2 "Partial postcranial skeleton" A saltasauroid titanosaur sauropod with possible affinities to the Saltasaurinae
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"Table 3.1," in Weishampel et al., 2004, p.49 An abelisauridRauhut, 2004Leanza et al., 2004, p.72 Enantiornithes indet. Indeterminate A distal humerus Koleken K. inakayali Norte de Cerro Bayo 1 Much of a partially articulated skeleton An abelisaurid. Neornithes indet. Indeterminate A distal ulna Similar to Anseriformes Theropoda indet. 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.Rougier et al., 2009, p.225
Mammals of the La Colonia Formation Genus Species Location Stratigraphic position Material Notes Images ArgentoditesA. coloniensis A possible gondwanatherian or multituberculate ColoniatheriumC. cilinskiiA meridiolestidan Ferugliotherium F. windhauseni A possible gondwanatherian or multituberculate ReigitheriumR. bunodontum A meridiolestidan NotopolythelesN. joelis A multituberculate
Snakes Fossils of madtsoiids, and perhaps boids, have been found in the formation. Snakes from the La Colonia Formation Genus Species Location Stratigraphic position Material Notes Images Alamitophis A. argentinus Trunk vertebra A madtsoiid snake Eomadtsoia E. ragei 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
References
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Further reading