Argentinosaurus
Argentinosaurus is a genus of titanosaurid sauropods, which lived 96-92 million years ago, during the Late Cretaceous period in Argentina. The only species of the genus is Argentinosaurus huinculensis. The name Argentinosaurus means "Argentine lizard" and the species name "huinculensis" refers to Plaza Huincul where the holotype was discovered.[1]
Depiction of Argentinosaurus huniculensis. By Nobu Tamura (http://spinops.blogspot.com) - File:Argentinosaurus BW.jpg, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=90887312
Known occurrences of Argentinosaurus huniculensis fossils.
Discovery and fossil history
Its first fossil was discovered and mistakenly identified as a petrified leg by Guillermo Heredia, rancher on his farm "Las Overas", near Plaza Huincul. He informed the local museum, the Museo Carmen Funes about his finding. The staff members of the museum excavated the fossil which turned to be a huge fibula, and stored it in the exhibition room of the museum.
Two years later, José F. Bonaparte, Argentine palaeontologist, and palaeontologists of the Museo Argentino de Ciencias Naturales did a larger excavation on the site, and found additional elements of the same individual, such as the vertebrae, underside of the sacrum and some ribs.[1][2] The bones were massive and extraordinary huge. One of the incomplete dorsal vertebra reconstructed to 1.59 metres high and the widest part of the sacrum was 1.23 metres long. The left fibula, which was originally described as tibia but have been reidentified by Gerardo Mazzetta and colleagues as fibula, was 1.55 metres long.[1][3] This specimen (MCF-PVPH 1) has been named and described by José F. Bonaparte and Rodolfo A. Coria as the holotype of a new genus and species, Argentinosaurus huinculensis in 1993.
Most parts of the Argentinosaurus skeleton are still unknown. From the same locality in 1996, a complete, 2.5 metres long femur was assigned to the holotype by Bonaparte. In 2004, an incomplete femur (MLP-DP 46-VIII-21-3) has been attributed to the holotype specimen by Geraldo V. Mazzetta who used the regressions on fibular length and femoral midshaft perimeter to estimate the total length of this incomplete femur which would be between 2.525 - 2.659 metres, nearly equivalent in size with the other, complete femur.[1] Further findings could help in understanding this gigantic sauropod.
Skeletal reconstuction of Argentinosaurus with all known fossile materials. By User:Slate Weasel - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=63524398
Description
The size of Argentinosaurus is still a matter of debate. It is difficult to estimate its true measures because of the fragmentary fossil remains of the species, but still it is referred as the biggest sauropod and biggest land animal that ever lived on Earth. It depending on the calculation method, the length of the Argentinosaurus was estimated between 30 and 39.7 metres and its weight was between 50 and 100 metric tonnes. However, the latest estimate suggests 35 metres in length and 70 tonnes in weight.
There are several other enormous titanosaur sauropods, like Dreadnoughtus schrani and Patagotitan mayorum, which are close to this size, but most of them, similarly to the Argentinosaurus, are known only from fragmentary remains.[4][5][6] Some diplodocoids, like Barosaurus lentus, could surpass Argentinosaurus in length, but due to their slender built they were lighter. To reduce their enourmous body mass, vertebrae and ribs of Argentinosaurus were lightened by tubes and air-filled chambers, similar to other large sauropods.[7][8]
Bony plates, called osteoderms, are known to be present on several titanosaurid sauropods such as the South American Saltasaurus, European Ampelosaurus and Magyarosaurus and Madagascarian Rapetosaurus. Although, there has not been found any osteoderms in case of Argentinosaurus, it does not disclose the possibility that they also possessed some sort of dermal armour. The function of osteoderms in titanosaurids is not well-known due to their scarcity. Because of their sparse arrangement, the main function was probably not the defence. There were found internal cavities in the Raperosaurus and Saltasaurus osteoderms, which may have played a role in mineral and nutrient storage. This function is reasonable for large animals living in highly seasonal climates and for females laying numerous large eggs.[9][10][11][12]
Skull materials, similarly to many titanosaurids, are still unknown. Although the diversity of titanosaurids is high and that may result in different skull shapes adapted to their lifestyle, based on fossils of other titanosaurid species, they likely had a small, wide head with large nostrils ("macronarian") and a nasal bone formed crest [13]. The forelegs and manus of Argentinosaurus are completely unknown, but based on the other titanosaurids, they probably had homogeneous, long, robust, columnar metacarpals with reduced or devoid digits. The feet had likely four toes, with one or two phalanges on each toe, similarly to other titanosaurs.[14][15]
Skeletal reconstuction of Argentinosaurus in the Fernbank Museum of Natural History. By Jeremy Thompson - https://www.flickr.com/photos/rollercoasterphilosophy/49326259442/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=85868958
Taxonomy and valid species
Argentinosaurus huinculensis is the type and only species of the genus Argentinosaurus. It was first classified in the Andesauridae along with two other South American titanosaurid genera, the Andesaurus and the Epachthosaurus.[1] In the last decades, the phylogenetical position changed multiple times within the branch of titanosaurids as more and more other titanosaurid species have been discovered.[15][16][17][18][19][20] Two studies published in 2019 found that Argentinosaurus belongs to the Lognkosauria clade along with other huge titanosaurids like the Patagotitan, Puertasaurus and Notocolossus.[21][22]
Paleobiology and paleoecology
Multiple factors made possible for the sauropods to reach their remarkable large size, especially the gigantic forms, such as Argentinosaurus. For example, the pneumatization of the axial skeleton and avian-style respiratory system lightened their massive body; their high metabolism made possible to be true endotherms and grow rapidly from early age.[38] Although, Argentinosaurus fossils are very scarce, based on its close relatives and the habitat it lived, we can speculate about its life history and behaviour. The area of the Huincul Formation was a floodplain with high-sinuosity fluvial system and covered with mixed evergreen forest. Dominant plants were the araucarias, cypress and basal magnoliophytes of these regions.[23] Under the canopy, big variety of horsetails, hornworts, liverworts, ferns, Selaginellales grew and covered the soil of the woodland and floodplain.[24]
The rich vegetation could support large herbivores such as the titanosaurid Choconsaurus baileywillisi and Argentinosaurus huinculensis, and the rebbachisaurid Cathartesaura anaerobica.[1][25][26] Besides sauropods, euiguanodontian ornithopods like the Anabisetia saldiviai inhabited the area.[27] Small and medium-sized carnivores, like the abelisaurid Skorpiovenator bustingorryi, Ilokelesia aguadagrandensis, Tralkasaurus cuyi, and the megaraptoran Aoniraptor libertatem likely preyed on the small herbivores and probably on the young and subadult sauropods.[27][28][29][30][31] Apex predators of the area at the time were the carcharodontosaurid Mapusaurus roseae and later the Meraxes gigas.[32][33] Other theropods also lived in the area, like the small noasaurid Huinculsaurus montesi and paravian Overoraptor chimentoi.[34][35] Besides the non-avian dinosaurus, rich vertebrate association known from the area. For example terrestrial crocodyliforms like the Araripesuchus patagonicus, neosuchian crocodilians, chelid turtles, sphenodontian rhynchocephalians, cladotherian mammals and lungfishes lived among the dinosaurs.[27][36][37] This environment posed many threats on Argentinosaurus hatchlings and juveniles but provided much resources to grow to one of the largest terrestrial being that ever walked on the Earth.
Dinosaurs from the Huincul Formation. By User:Slate Weasel - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=84930907
Author: Péter Imre Fábián, Biologist MSc student
Scientific references
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