Antarctosaurus
Antarctosaurus | |
---|---|
Hypothetical Antarctosaurus wichmannianus skull diagram showing the bones illustrated by von Huene in 1929. It's not certain that the mandible and braincase belong to the same individual or even same genus. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | †Sauropodomorpha |
Clade: | †Sauropoda |
Clade: | †Macronaria |
Clade: | †Titanosauria |
Clade: | †Colossosauria |
Genus: | †Antarctosaurus von Huene, 1929 |
Species | |
Synonyms | |
|
Antarctosaurus (
The type species, A. wichmannianus, is controversial because there is uncertainty as to whether all the described remains belong to the same individual or even genus. The second species, A. giganteus, is considered dubious, but the fragmentary remains represent one of the largest dinosaurs known.
Discovery and species
Antarctosaurus wichmannianus is the type species of the genus, named in 1929 after the discoverer of its remains in 1912, geologist Ricardo Wichmann.[2] Von Huene used the name A. wichmannianus to describe a large assemblage of bones, which are considered to come from the Anacleto Formation in Río Negro Province of Argentina,[3] which is probably early Campanian in age.[4] Two additional limb bones, found in the Chubut Province in 1924, were also referred to A. wichmannianus by von Huene in 1929.[2] Later studies, however, have doubted their referral to the species.[5]
Von Huene also named a fragmentary second species of Antarctosaurus in the same 1929 monograph, which he tentatively called cf. Antarctosaurus giganteus because of its enormous size.[3] These fossils were recovered in Neuquén Province of Argentina, from the Plottier Formation,[3][6] which dates to the Coniacian-Santonian stages of the Late Cretaceous Period.[4] The Plottier, like the younger Anacleto, is a member of the Neuquén Group.[4]
Very few remains are known of this species and it is regarded as a
In 1933, Von Huene and Charles Matley described another species, Antarctosaurus septentrionalis, meaning "northern". The remains were found in the Lameta Formation of Madhya Pradesh State in India.[11][12] This species does preserve important anatomical information but has since been assigned to its own genus in 1994; Jainosaurus.[13]
Antarctosaurus jaxarticus from
In 1970, two fragmentary limb bones and a partial vertebra were found in the Adamantina Formation (originally described as Bauru Formation;[19] has also been reported as the São José do Rio Preto Formation[20]) of the northern Paraná Basin in Brazil. The remains were described by their discoverers Fahad Moysés Arid and Luiz Dino Vizotto in 1971 as A. brasiliensis.[19][21] Other researchers have considered this species as either, a nomen dubium,[7][8][21] or an indeterminate titanosaur.[22]
Description
Describing Antarctosaurus is problematic because the type species consists of elements that are of questionable association and none of the species described are known from complete remains, which has caused a confused taxonomy of the genus.[7] Of the four additional species that have been assigned to Antarctosaurus over the years, three have been considered dubious[3][7][17][21] and "Antarctosaurus" septentrionalis, was given its own genus, Jainosaurus.[13]
The remains that have been described belong to
Antarctosaurus wichmannianus
The assemblage of fossil remains that became known as A. wichmannianus were given the specimen number MACN 6904.[2] The known material includes several skull fragments, including a braincase and an incomplete mandible (lower jaw), a cervical (neck) vertebra, a caudal (tail) vertebra, rib fragments, and numerous limb bones including a femur which measures 1.39 meters (4.6 ft) tall. None of the individual fossils were designated the holotype specimen so MACN 6904 is considered to be an assemblage of syntypes.[17] The total length of A. wichmannianus has been estimated at around 17 meters (56 ft).[24]
An additional femur and tibia were also referred by von Huene to A. wichmannianus; the femur, FMNH P13019, is over 1.85 meters (6.1 ft) tall. In one study the dimensions of this femur were used in a regression analysis to estimate the mass of A. wichmannianus at about 34 metric tons (37 short tons).[25] The referral of the additional femur and tibia has been questioned by later researchers. In 2003 Jaime Eduardo Powell tentatively referred them to cf. Argyrosaurus and in 2012 Philip Mannion and Alejandro Otero considered it an indeterminate titanosaur.[5]
The incomplete mandible attributed to A. wichmannianus is squared-off at the front with each dentary bone being ''L'' shaped.[26] The teeth were restricted to the front of the lower jaw and were small and slender.[3] The squared-off jaws suggest specialised feeding habits, such as feeding near a surface plane like low vegetation on the ground or floating plants in water.[8]
The back of the skull and the remainder of the skeleton are usually regarded as titanosaurian by researchers, although they do not necessarily belong to the same type of titanosaur.[7][27][32] In 2005, Jeffrey Wilson considered the braincase as being referable to Nemegtosauridae but noted that other skull remains require further study.[17] A study, published in 2012 by Ariana Paulina Carabajal, CT scanned the A. wichmannianus braincase which revealed the complete brain endocast and the inner ear structures. The brain endocast and inner ear share several features with other titanosaurids such as short olfactory tracts and olfactory bulbs that are horizontally projected.[33]
Powell compared the width of the cranium to the length of the limb bones of both A. wichmannianus and Saltasaurus; this led him to conclude that the skull was proportionally small in A. wichmannianus, this might imply that the skull and limb elements could belong to different individuals or a different taxa. He noted, however, that the comparison was potentially misleading because the overall anatomy of Saltasaurus is shorter and stouter which might facilitate a bigger skull.[8]
Von Huene assigned two tarsal (ankle) bones to A. wichmannianus, which he described as an astragalus and a calcanium. Powell suggested it's possible that the calcanium described by von Huene is actually the astragalus of a smaller individual. He also noted that the astragalus seems too small to belong to the same individual as the tibia, being only about half the width.[8]
Von Huene described a caudal vertebra which was found close to the skull material. This vertebra was the first caudal, belonging to the base of the tail just after the sacrum (vertebrae attached to the hip). The vertebra features a biconvex centrum, a feature shared with other titanosaurs.[3] Von Huene noted that the first caudal could possibly belong to Laplatasaurus.[3][27]
With the exception of an incomplete cervical vertebra and the questionable first caudal, there are no vertebrae that link the skull to the limb material.[27] There is a lack of field documentation to aid in the referral of all the material to one individual.[17][34] Powell thought it was probable that von Huene correctly assigned the material to A. wichmannianus, arguing that von Huene would have been able to communicate with the discoverers and would have had access to photographs of the discovery site.[8]
"Antarctosaurus" giganteus
The type specimen of A. giganteus, MLP 26-316, includes a left and right femur, a partial left and right pubis, the distal end of a damaged tibia, numerous rib and distal caudal vertebrae fragments, and six large and unidentifiable bones.[2] The two gigantic femora measure 2.35 meters (7.7 ft) in length, which are among the largest of any known sauropod.[25] Even though the femurs are large, they are also somewhat gracile in construction.[3]
A reconstruction of A. giganteus, published in 1956 by Carlos Rusconi, was given a length around 30 meters (98 ft). In 1969, van Valen considered it as similar in size to
In 2016, using equations that estimate body mass based on the circumference of the humerus and femur of quadrupedal animals, it was estimated to be 39.5 metric tons (43.5 short tons) in weight.[39] In 2019, Gregory S. Paul estimated the mass of A. giganteus in the 45 to 55 metric tons (50 to 61 short tons) range, based on newer titanosaur reconstructions.[40] In 2020 Molina-Pérez and Larramendi estimated its length at 30.5 meters (100 ft) and its weight similar to Paul's estimation at 45 metric tons (50 short tons).[41] Due to the incompleteness of the remains, any size estimates are subject to a large amount of error.[9]
"Antarctosaurus" jaxarticus and "Antarctosaurus" brasiliensis
"Antarctosaurus" jaxarticus and "Antarctosaurus" brasiliensis are both known from very fragmentary remains.
"Antarctosaurus" jaxarticus is known from a single femur which was briefly reported as resembling a femur attributed to Jainosaurus (then called "Antarctosaurus" septentrionalis).[14][16] Paleontologist Teresa Maryańska noted that, whilst A. jaxarticus was named, it was not properly described or diagnosed.[15] The femur possibly belongs to the titanosaur clade Lithostrotia.[16]
The type specimen of "Antarctosaurus" brasiliensis is only known from three fragmentary bones that are titanosaurian in nature; a partial left femur GP-RD-2, a partial right
Classification
Antarctosaurus has been included in few phylogenetic analyses, only being added to the matrix of Philip Mannion et al. in 2019. It was coded along with Vahiny, Jainosaurus, Normanniasaurus and additional non-titanosaurs. Antarctosaurus placed as sister taxon to a clade of Vahiny and Jainosaurus, consistently close to taxa of the clade Lognkosauria.[42]
References
- ^ Wichmann, R. (1916). "Las capas con Dinosaurios en la Costa sur del Río Negro, frente a General Roca". Physis. 11: 258–262.
- ^ a b c d e von Huene, F. 1929. Los saurisquios y ornitisquios del Cretáceo Argentino. Anales del Museo de La Plata (series 3) 3: 1–196. [In Spanish]
- ^ OCLC 259716158.
- ^ OCLC 860681404.
- ^ S2CID 86762374.
- ISSN 1094-8074.
- ^ a b c d e f Upchurch, P., Barrett, P.M, & Dodson, P. 2004. Sauropoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). The Dinosauria (2nd Edition). Berkeley: University of California Press. Pp. 259-322.
- ^ OCLC 52391340.
- ^ JSTOR 1441947.
- ^ Bonaparte, J. F.; Gasparini, Z. B. (1979). "Los sauropodos de los grupos Neuquén y Chubut, y sus relaciones cronologicas". Actas del Congreso Geológico Argentino. II: 393–406.
- ^ Von Huene, F.; Matley, C.A. (1933). "Cretaceous Saurischia and Ornithischia of the central provinces of India". Palaeontologia Indica. 21: 1–74.
- )
- ^ a b Hunt, A.P., Lockley M., Lucas S. & Meyer C., 1995, "The global sauropod fossil record", In: M.G. Lockley, V.F. dos Santos, C.A. Meyer, and A.P. Hunt, (eds.) Aspects of sauropod paleobiology, GAIA 10: 261-279
- ^ a b c Riabinin, A. N. (1938). "Some results of the studies of the Upper Cretaceous dinosaurian fauna from the vicinity of the Station Sary-Agach, south Kazakhstan". Problems of Paleontology. 4: 130–135.
- ^ )
- ^ ISSN 0195-6671.
- ^ S2CID 54070651.
- ^ Weishampel, D. B.; Dodson, P.; Osmólska, H. (1990). The Dinosauria. Berkeley: University of California Press.
- ^ a b c Arid, F.M. & Vizotto, L.D. 1971. Antarctosaurus brasiliensis, um novo saurópode do Crétaceo superior do sul do Brasil. In: Congresso Brasileiro de Geologia 25: 297-305. [In Portuguese]
- ^ Lori, F. V.; Marinho, D. S.; Silva Junior, J. C. G.; Paschoa, L. S. (2017). "A Paleofauna Da Formação São José Do Rio Preto (Bacia Bauru, Cretáceo Superior)". Conference: XXV Congresso Brasileiro de Paleontologia.
- ^ a b c Candeiro, C.; da Silva Marinho, T.; Carlos de Oliveira, E. (2004). "Distribuição geográfica dos dinossauros da Bacia Bauru (Cretáceo Superior)". Revista Sociedade & Natureza. 16 (30): 33–55.
- PMID 11151018.
- OCLC 858764960.
- )
- ^ S2CID 56028251.
- ^ PMID 30569970.
- ^ .
- PMID 10558986.
- hdl:2027.42/73066.
- S2CID 33590452.
- ^ PMID 26191585.
- )
- S2CID 24555402.
- S2CID 131595654.
- ^ G.S. Paul, 1994, "Big sauropods – really, really big sauropods", The Dinosaur Report, The Dinosaur Society, Fall, p. 12–13
- S2CID 56215581.
- ^ Holtz, Thomas R. (2012). "Genus List for Holtz (2007) Dinosaurs" (PDF).
- ^ Holtz, Thomas R. "Supplementary Information to Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages".
- PMID 26777391.
- S2CID 210840060.
- Bibcode:2020dffs.book.....M.
- PMID 31598266.
External links
- Post Archived March 3, 2016, at the Wayback Machine on the Dinosaur Mailing List Archived November 5, 2020, at the Wayback Machine detailing the various species of Antarctosaurus and the remains assigned to them.
- A blog post detailing the problematic A.wichmannianus.
- A blog post detailing the species that have been referred to Antarctosaurus.
- A blog post discussing the material of Antarctosaurus wichmannianus and showing a reconstruction of the skull