Giganotosaurus

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Not to be confused with Gigantosaurus.
Giganotosaurus
Temporal range: Late Cretaceous, 97Ma
Giganothosaurus.jpg
Replica skeleton
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Suborder: Theropoda
Clade: Carnosauria
Family: Carcharodontosauridae
Subfamily: Carcharodontosaurinae
Tribe: Giganotosaurini
Genus: Giganotosaurus
Coria & Salgado, 1995
Species: † G. carolinii
Binomial name
Giganotosaurus carolinii
Coria & Salgado, 1995

Giganotosaurus (/ˌɡəˌntəˈsɔrəs/ JY-gə--NOH-tə-SOR-əs[1] or GIG-ə-NOT-o-SAW-rus meaning "giant southern lizard"[2]) is a genus of carcharodontosaurid dinosaurs that lived in what is now Argentina during the early Cenomanian age of the Late Cretaceous Period,[3] approximately some 100 to 97 million years ago.[4] It included some of the largest known terrestrial carnivores, with known individuals equaling or slightly bigger than the size of the largest of the genera Tyrannosaurus and Carcharodontosaurus, but not as large as those of Spinosaurus.

Description

Artist's impression

The skeleton of the holotype specimen (MUCPv-Ch1) is about 70% complete and includes parts of the skull, a lower jaw, pelvis, hindlimbs and most of the backbone, missing only the premaxillae, jugals, quadratojugals, the back of the lower jaws and the forelimbs. A second specimen (MUCPv-95) has also been identified, found in 1988 by Jorge Calvo and consisting of a fragment of a lower jaw,[5] said to be 8% larger than the corresponding part in the first specimen.[6]

The skull of Giganotosaurus is large; that of the holotype was in 1995 estimated at 1.53 m (5.0 ft) in length.[7] Even though the original authors briefly claimed the length to be up to 1.8 m (5.9 ft)[8]—leading to an estimate of 1.95 m (6.4 ft) skull length for the referred specimen[6]—this claim was not repeated by subsequent workers[9] and one of the original authors was in 2002 co-writer of an article giving a holotype skull length of 1.6 m (5.2 ft).[3] Some have claimed that even the original estimate was too long and believe the skull to be almost exactly comparable to the one of Tyrannosaurus in length.[10] The skull is slender and elongated in build, with rugose areas on the edges of the snout top and above the eye. The supratemporal openings were overhung by the edges of the skull roof where the jaw muscles of each side directly attached instead of meeting each other at a midline skull crest. The back of the skull as preserved is strongly inclined forwards, bringing the jaw joints far behind the attachment point of the neck.[3] The endocast of Giganotosaurus has a volume of 275 cc (16.8 cu in)[3] and including the olfactory bulbs, it was 19% longer than that of the related theropod, Carcharodontosaurus saharicus.[11]

A size comparison between Giganotosaurus (second from the right) and other theropods

The shoulder blade was very short and thick, with sudden kinks in its shaft. The ischium had a paddle-shaped end; the thigh bone, 1.43 m (4.7 ft) long in the holotype, had a head that was pointing relatively upwards.[12] The mid dorsal vertebrae carried rather high spines. The total length of the holotype has been estimated between 12.2 and 12.5 m (40 and 41 ft),[7][13] the largest specimen is 13.2 m (43 ft),[4] and the weight between 6.5 and 13.8 tonnes (14,330 and 30,420 lb).[14][15]

Paleobiology

Artist's impression

Titanosaur fossils belonging to Andesaurus and Limaysaurus have been recovered near the remains of Giganotosaurus, leading to speculation that these carnivores may have preyed on the giant herbivores. Fossils of the related carcharodontosaurid Mapusaurus grouped closely together may indicate pack hunting, a behavior that could possibly extend to Giganotosaurus itself.


Blanco and Mazzetta (2001) estimated that for Giganotosaurus a growing imbalance when increasing its velocity would pose an upper limit of 14 metres per second (50 km/h; 31 mph) to its running speed, after which minimal stability would have been lost.[16]

In 2005 François Therrien e.a. estimated that the bite force of Giganotosaurus was three times less than that of Tyrannosaurus and that the lower jaws were optimised for inflicting slicing wounds; the point of the mandibula was reinforced to this purpose with a "chin" and broadened to handle smaller prey.[17]

Classification

Restored skeleton
Skull reconstruction cast

Giganotosaurus, along with relatives like Tyrannotitan, Mapusaurus and Carcharodontosaurus, are members of the carnosaur family Carcharodontosauridae. Both Giganotosaurus and Mapusaurus have been placed in their own subfamily Giganotosaurinae by Coria and Currie in 2006 as more carcharodontosaurid dinosaurs are found and described, allowing interrelationships to be calculated.[13]

The following cladogram after Novas et al., 2013, shows the placement of Acrocanthosaurus within Carcharodontosauridae.[18]



Allosaurus


Carcharodontosauridae

Neovenator



Eocarcharia



Concavenator




Acrocanthosaurus




Shaochilong


Carcharodontosaurinae

Carcharodontosaurus


Giganotosaurini

Tyrannotitan




Mapusaurus



Giganotosaurus









Discovery and species

Type specimen at Museo de El Chocón (the skull is a replica)

The most complete find of Giganotosaurus was made by Rubén Dario Carolini, an amateur fossil hunter who, on 25 July 1993, discovered a skeleton in deposits of Patagonia (southern Argentina) in what is now considered the Candeleros Formation.[3] The discovery was scientifically reported in 1994.[19] The initial description was published by Rodolfo Coria and Leonardo Salgado in the journal Nature in September 1995.[7] The type species is Giganotosaurus carolinii. The generic name means "giant southern lizard", derived from the Ancient Greek gigas/γίγας meaning "giant", notos/νότος meaning "southern" and -sauros/-σαύρος meaning "lizard".[20] The specific name honours Carolini.

Paleoecology

Giganotosaurus was probably the apex predator in its ecosystem. It shared its environment with titanosaurian sauropod Andesaurus and the rebbachisaurid sauropods Limaysaurus and Nopcsaspondylus. Iguanodont and ornithischian remains have reportedly been found there too. Large abelisaurid theropod Ekrixinatosaurus also shared the environment, and was possibly a competitor at times. Smaller predators also inhabited the area. These included dromaeosaurid Buitreraptor, alvarezsaurid Alnashetri, and basal coelurosaurian Bicentenaria. The primitive snake Najash lived here as well, along with turtles, fish, frogs, and cladotherian mammals. Pterosaurs also lived in the area.[21]

References

  1. ^ Academy of Natural Sciences: Giganotosaurus
  2. ^ Haines, T.; Chambers, P. (2007). "The Complete Guide to Prehistoric Life". Italy: Firefly Books Ltd. pp. 116–117. ISBN 1-55407-181-X. 
  3. ^ a b c d e Coria, R.A. and Currie, P.J. (2002). "Braincase of Giganotosaurus carolinii (Dinosauria: Theropoda) from the Upper Cretaceous of Argentina." Journal of Vertebrate Paleontology, 22(4): 802-811.
  4. ^ a b Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
  5. ^ J.O. Calvo, 1990, "Un gigantesco theropodo del Miembro Candeleros (Albiano–Cenomaniano) del la Formación Río Limay, Patagonia, Argentina", VII Jornadas Argentinas de Paleontología de Vertebrados. Ameghiniana 26(3-4): 241
  6. ^ a b Calvo, J.O. and Coria, R.A. (1998) "New specimen of Giganotosaurus carolinii (Coria & Salgado, 1995), supports it as the largest theropod ever found." Gaia, 15: 117–122. pdf link
  7. ^ a b c Coria, R.A. & Salgado, L. (1995). A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature 377: 225-226
  8. ^ Coria, R. & Salgado, L., 1996, "Dinosaurios carnívoros de Sudamérica", Investigación Sciencia, 237: 39-40
  9. ^ Currie, Philip J.; & Carpenter, Kenneth. (2000). "A new specimen of Acrocanthosaurus atokensis (Theropoda, Dinosauria) from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA". Geodiversitas 22 (2): 207–246. 
  10. ^ Matthew T. Carrano, Roger B. J. Benson & Scott D. Sampson, 2012, "The phylogeny of Tetanurae (Dinosauria: Theropoda)", Journal of Systematic Palaeontology, 10(2): 233
  11. ^ Ariana Paulina Carabajal & J.I. Canale, 2010, "Cranial endocast of the carcharodontosaurid theropod Giganotosaurus carolinii Coria & Salgado, 1995", Neues Jahrbuch fuer Geologie & Palaeontologie, Abhandlungen 258(2): 249-256
  12. ^ J.O. Calvo, 1999, "Dinosaurs and other vertebrates of the Lake Ezequiel Ramos Mexía area, Neuquén-Patagonia, Argentina", In: Y. Tomida, T. H. Rich, and P. Vickers-Rich (eds.), Proceedings of the Second Gondwanan Dinosaur Symposium, National Science Museum Monographs 15: 13-45
  13. ^ a b Coria, R.A. and Currie, P.J. (2006). "A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina." Geodiversitas, 28(1): 71-118. pdf link
  14. ^ Seebacher, F. (2001). "A new method to calculate allometric length-mass relationships of dinosaurs". Journal of Vertebrate Paleontology 21 (1): 51–60. doi:10.1671/0272-4634(2001)021[0051:ANMTCA]2.0.CO;2. ISSN 0272-4634. 
  15. ^ Therrien, F.; Henderson, D.M. (2007). "My theropod is bigger than yours...or not: estimating body size from skull length in theropods". Journal of Vertebrate Paleontology 27 (1): 108–115. doi:10.1671/0272-4634(2007)27[108:MTIBTY]2.0.CO;2. ISSN 0272-4634. 
  16. ^ Blanco, R. Ernesto; Mazzetta, Gerardo V. (2001). "A new approach to evaluate the cursorial ability of the giant theropod Giganotosaurus carolinii". Acta Palaeontologica Polonica 46 (2): 193–202. 
  17. ^ Therrien, François; Henderson, Donald M.; Ruff, Christopher B., 2005, "Bite Me: Biomechanical models of theropod mandibles and implications for feeding". In: Carpenter, Kenneth. The Carnivorous Dinosaurs. Life of the Past. Indiana University Press. pp. 179–237
  18. ^ Novas, F. E.; Agnolín, F. L.; Ezcurra, M. N. D.; Porfiri, J.; Canale, J. I. (2013). "Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia". Cretaceous Research 45: 174. doi:10.1016/j.cretres.2013.04.001.  edit
  19. ^ R.A. Coria and L. Sagado, 1994, "A giant theropod from the middle Cretaceous of Patagonia, Argentina", Journal of Vertebrate Paleontology 14(3, supplement):22A
  20. ^ Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4. 
  21. ^ Leanza, H.A.; Apesteguia, S.; Novas, F.E. & de la Fuente, M.S. (2004): Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages. Cretaceous Research 25(1): 61-87. doi:10.1016/j.cretres.2003.10.005 (HTML abstract)

External links