Aucasaurus

Aucasaurus; Temporal range: Late Cretaceous, 83 Ma PreЄ Є O S D C P T J K Pg N ↓
	Mounted skeleton reconstruction
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Family:	†Abelisauridae
Tribe:	†Carnotaurini
Genus:	†Aucasaurus; Coria, Chiappe & Dingus, 2002
Type species
	Aucasaurus garridoi; Coria, Chiappe & Dingus, 2002

Aucasaurus was a genus of medium-sized theropod dinosaur from Argentina that lived during the Santonian - Campanian stage of the Anacleto Formation. It was smaller than the related Carnotaurus, although more derived in some ways, such as its extremely reduced arms and almost total lack of fingers.^[1] The type skeleton is complete to the thirteenth caudal vertebra, and so is relatively well understood, and is the most complete abelisaurid yet described. However, the skull is damaged, causing some paleontologists to speculate that it was involved in a fight prior to death.

Description

Reconstruction

Size compared to a human

Aucasaurus short, deep-snouted skull was not as short or as deep-snouted as that of Carnotaurus. Also, instead of horns, it had a pair of low ridges above each eye.^[2]

In 2010, Gregory S. Paul estimated its body length at 5.5 metres, its weight at 700 kilograms.^[3] In 2016, its length was estimated to be 6.1 metres (20 ft) in a comprehensive analysis of abelisaur size.^[4]

Forelimbs and hands

Aucasaurus small arms were also like that of its horned relative, but were proportionally longer due to its small size, and the bones lacked the bony processes and some unusual proportions present in Carnotaurus. The hand of Aucasaurus was unusual: four metacarpals were present, but the first and fourth lacked fingers. The second and third had fingers, but they were quite short and had no claws.^[2]

Braincase

3D scan of the braincase

A study was done on the braincase of Aucasaurus in 2015 by Ariana Paulina-Carabajal and Cecilia Succar, in which the skull material was scanned using a medical CT machine. Virtual three-dimensional inner ear and cranial endocasts were obtained and visualized using the imagine software at the University of Alberta. A latex cranial endocast was also made. The forebrain, midbrain, and hindbrain resemble the morphology described for the abelisaurids Majungasaurus and Indosaurus. However, Aucasaurus exhibits a floccular process that is relatively larger than that of Majungasaurus. In Aucasaurus the flocculus is enclosed in an 8-shaped floccular recess, similar in shape and size to that observed in Abelisaurus, suggesting that the two Patagonian taxa were capable of a slightly wider range of movements of the head. The labyrinth of the inner ear is similar in shape and size to the semicircular canals of Majungasaurus, although the lateral semicircular canal is shorter in Aucasaurus.^[5]

Discovery

Aucasaurus is known from finds in the Rio Colorado Formation, a Late Cretaceous formation in Argentina that has yielded many dinosaur fossils. Numerous sauropod eggs are also known from this deposit.^[2]

Classification

Aucasaurus was closely related to Carnotaurus and they are united in the Carnotaurini.^[2]

Below is a cladogram by Canalle et al. in 2009.^[6]

	Aucasaurus

	Carnotaurus

Ilokelesia

	Skorpiovenator

	Ekrixinatosaurus

References

↑ Coria, R. A.; Chiappe, L. M.; Dingus, L. (2002). "A new close relative of Carnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia". Journal of Vertebrate Paleontology. 22 (2): 460. doi:10.1671/0272-4634(2002)022[0460:ANCROC]2.0.CO;2.
1 2 3 4 Benton, Michael J. (2012). Prehistoric Life. Edinburgh, Scotland: Dorling Kindersley. p. 320. ISBN 978-0-7566-9910-9.
↑ Paul, G.S., 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 79
↑ Grillo, O. N.; Delcourt, R. (2016). "Allometry and body length of abelisauroid theropods: Pycnonemosaurus nevesi is the new king". Cretaceous Research. doi:10.1016/j.cretres.2016.09.001.
↑ Paulina-Carabajal, A.; Succar, C. (2015). "The endocranial morphology and inner ear of the abelisaurid theropod Aucasaurus garridoi". Acta Palaeontologica Polonica. doi:10.4202/app.2013.0037.
↑ Canale, J. I.; Scanferla, C. A.; Agnolin, F. L.; Novas, F. E. (2008). "New carnivorous dinosaur from the Late Cretaceous of NW Patagonia and the evolution of abelisaurid theropods". Naturwissenschaften. 96 (3): 409–414. Bibcode:2009NW.....96..409C. doi:10.1007/s00114-008-0487-4. PMID 19057888.

External links

The Theropod Database on Aucasaurus

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[1] Coria, R. A.; Chiappe, L. M.; Dingus, L. (2002). "A new close relative of Carnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia". Journal of Vertebrate Paleontology. 22 (2): 460. doi:10.1671/0272-4634(2002)022[0460:ANCROC]2.0.CO;2.

[Michael_J._Benton,_Prehistoric_Life-2] 1 2 3 4 Benton, Michael J. (2012). Prehistoric Life. Edinburgh, Scotland: Dorling Kindersley. p. 320. ISBN 978-0-7566-9910-9.

[3] Paul, G.S., 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 79

[4] Grillo, O. N.; Delcourt, R. (2016). "Allometry and body length of abelisauroid theropods: Pycnonemosaurus nevesi is the new king". Cretaceous Research. doi:10.1016/j.cretres.2016.09.001.

[paulina2015-5] Paulina-Carabajal, A.; Succar, C. (2015). "The endocranial morphology and inner ear of the abelisaurid theropod Aucasaurus garridoi". Acta Palaeontologica Polonica. doi:10.4202/app.2013.0037.

[canalle-6] Canale, J. I.; Scanferla, C. A.; Agnolin, F. L.; Novas, F. E. (2008). "New carnivorous dinosaur from the Late Cretaceous of NW Patagonia and the evolution of abelisaurid theropods". Naturwissenschaften. 96 (3): 409–414. Bibcode:2009NW.....96..409C. doi:10.1007/s00114-008-0487-4. PMID 19057888.