Aucasaurus

*Aucasaurus garridoi*

***Aucasaurus*** was a genus of medium-sized theropod dinosaur from Argentina that lived during the Santonian 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. 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[who?] to speculate that it was involved in a fight prior to death.

## Discovery

*Aucasaurus* is not a very well-known dinosaur. However, it's quite famous in the paleontology universe because the skeleton that we know this theropod from is the most complete of any abelisaurid. It was first discovered in the badlands of Argentina in 1999 but wasn't officially named until three paleontologists named Coria, Chiappe, and Dingus came up with the name *Aucasaurus*, meaning "Auca lizard", after the place it was first found in.

Currently we have only one specimen of this rare theropod but the fact that it's nearly intact helps us piece together a lot about it. One interesting feature about the specimen found in Patagonia was its skull. It seemed to have been damaged shortly before it died. It's not quite known what may have been the cause of this but most scientists agree that it was likely caused by two *Aucasaurus* that were fighting and this specific specimen was bitten on the face and likely died shortly after.

*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.

## Description

*Aucasaurus* is an abelisaurid closely related to *Carnotaurus* and *Majungasaurus*. It grew to be about 4.3 metres (14.1 ft) long and is said to weigh 1,500 lbs. This makes it quite small compared to other abelisaurids and theropods, since its close relative *Carnotaurus* grew to be about 30 feet (9 meters) long and nearly 3 tons in weight. It is depicted as a pack hunter, hunting dinosaurs like *Saltasaurus*. The name *Aucasaurus* comes from the words: "Auca" after the site of its discovery, Auca Mahuevo, and "Sauros" which means lizard. It likely fed on small to medium-sized sauropods like *Saltasaurus*, and was a second predator after the carnosaurs like *Giganotosaurus*, *Mapusaurus*, and *Tyrannotitan*. It had long, sturdy legs and very short arms that were deemed close to useless.

*Aucasaurus* became famous by having the most complete fossil of any known abelisaurid species. It was a medium sized abelisaurid theropod that coexisted, hunted and likely came into conflict with several other species of dinosaurs and theropods of its timescale and habitat. It grew to be about 4.3  metres long and is said to weigh 1,500 kg. This theropod live around several species of sauropods, albeit specifically considering the size difference, hunting or even injuring any adult sauropod would be impossible and suicidal for the animal, hatchling, juvenile and subadult Sauropods are an entirely different subject. In fact there are several somewhat speculative interpretations of this particular theropod efficiently raiding the nests of Sauropods.

That aside this abelisaurid would be effective at hunting small to medium sized prey, considering its agility and physical abilities. This theropods behavior is unknown, there are interpretations of it being a pack animal, albeit abelisaurid social behavior is unclear, aside from one specific species *Majungasaurus* being cannibalistic - although it is unclear if the cannibalism cases represent scavenging the dead similar to many carnivores of modern era, or are active hunting.

They were so small in fact that it's debated whether or not it even had fingers at all. Its skull was somewhat short, but was boxy and thick, suggesting it had powerful jaws. It's teeth were also very thick and durable, like most abelisaurids, and were perfectly designed for ripping off chunks of flesh from carcasses.

### Forelimbs and Hands

*Aucasaurus* small arms were also alike 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.

## Classification

Aucasaurus was closely related to Carnotaurus and they are united in the Carnotaurini.

Below is a cladogram by Canalle et al. in 2009.

## JPInstitute.com Description

Aucasaurus, a very recent discovery, was a medium-sized meat-eater that seems to have been similar to Carnotaurus. It was smaller than Carnotaurus, which means that it may have hunted different types of prey than its larger relative. This discovery was exciting because many of the bones were found, along with skin impressions. Also, the fossil was found with its skull broken from what appears to have been a fight to the death.

As of this writing, Aucasaurus has not yet been formally described. It is considered the most complete abelisaur yet found.

## Links

http://web.archive.org/web/20031006081536fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_aucas.html#
https://web.archive.org/web/20080505070853/http://kids.yahoo.com/dinosaurs/306--Aucasaurus