Gualicho Sticks Two Fingers Up at T. rex

Gualicho shinyae – A Dinosaur with Arms Reminiscent of Tyrannosaurus rex

With the formal publication of the scientific paper describing a new species of carnivorous dinosaur from Argentina, the Theropoda just became a little bit more curious.  Gualicho shinyae has been erected and it shows both Tetanuran (stiff tailed) and Ceratosaurian anatomical traits.  G. shinyae can also lay claim to being the most basal member of the Tetanurae clade to exhibit the reduction of digit III on the hand.  Reports in the media have compared this new Late Cretaceous South American dinosaur with Tyrannosaurus rex.  These two dinosaurs may have had very reduced arms and only two fingers on each hand, but Gualicho is not closely related to the “King of the Tyrant Lizards”.  In fact it seems that Gualicho shinyae is an example of convergent evolution, that is, not closely related organisms evolve independently similar traits as a result of having to adapt to similar environments or ecological niches.

Just why many large meat-eating dinosaurs had reduced arms and vestigial digits remains a mystery.

An Illustration of a the New Dinosaur from Argentina


Picture Credit: Jorge González and Pablo Lara

In the picture above two predatory dinosaurs (Gualicho shinyae) ambush a flock of hypsilophodonts.

The Mystery Over Short Arms and Reduced Digits in Theropod Dinosaurs

The third digit is reduced to nothing more than a metacarpal splint, very reminiscent of tyrannosaurids and just like all the known Late Cretaceous Tyrannosaurs, the arms are also reduced in proportion to the body size.  Gaulicho is estimated to have been at least six metres long, but the forelimbs are no bigger than those of a child.  The left forelimb was recovered along with a short section of vertebrae from the back, the end portion of the tail, elements of both hind limbs including an articulated foot plus a left scapulocoracoid  A couple of rib bones and some gastralia (belly ribs) were also excavated.  The rest of the skeleton had been lost to erosion, but from these remains the researchers, which included scientists from the Field Museum (Chicago), the Dinosaur Institute of Los Angeles as well as palaeontologists from  Buenos Aires and Rio Negro Province, suggest that this new dinosaur is a neovenatorid with close affinities to the North African dinosaur Deltadromeus.

An Illustration of the Likely Skeleton of G. shinyae

Gualicho dinosaur drawing.

The white shaded bones show the fossils of Gualicho that have been found.

Picture Credit: PLoS One with additional annotation by Everything Dinosaur

Discovered back in 2007, the specimen, which consists of around 5% of the total skeleton was excavated and prepared by staff of the Museo Patagónico de Ciencias Naturales.  The genus name is derived from “Gualichu”, a spirit revered by Patagonia’s Tehuelche people.  The field team encountered quite a lot of misfortune during the 2007 expedition and during the subsequent preparation work.  Researchers joked about the “curse of Gualichu”.  The species name honours Ms Akiko Shinya, the Chief Fossil Preparator at the Field Museum (Chicago).  It was Ms Akiko who found the first fossil evidence of this new type of dinosaur during the 2007 expedition to the Neuquén Basin of Patagonia (southern Argentina).

Chief Fossil Preparator Ms Akiko Shinya Showing where the Fossils were Found


Picture Credit: PLoS One (Photo by Peter Makovicky)

Corresponding author Peter Makovicky (Field Museum) stated:

“Gualicho is kind of a mosaic dinosaur, it has features that you normally see in different kinds of Theropods.  It’s really unusual, it’s different from the other carnivorous dinosaurs found in the same rock formation, and it doesn’t fit neatly into any category.”

Estimated to have weighed around 450 kilogrammes and to have been about six metres long, Gualicho has been assigned to the Allosauria clade and placed within the Neovenatoridae family, however, its exact taxonomic position remains unclear.  The scientists conclude that it resembles Deltadromeus, a contemporaneous Theropod known from North Africa.

Cenomanian Faunal Stage

The fossils of G. shinyae were excavated from sandstone strata located close to the base of the Huincul Formation.  Everything Dinosaur estimate that this dinosaur roamed what was to become Patagonia some ninety-five million years ago (Cenomanian faunal stage of the Late Cretaceous).

The New Dinosaur Discovery Adds to the Faunal Diversity of the Lower Part of the Neuquén Group

Gualicho adds to the faunal diversity of the Upper Cretaceous sediments.

A schematic stratigraphic diagram showing the position of the Gualicho fossil find.

Picture Credit: PLoS One

The picture above shows a schematic diagram of the lower part of the Neuquén Group of Upper Cretaceous strata exposed in the Neuquén Basin with the approximate level at which the holotype of Gualicho shinyae was collected from the base of the Huincul Formation.  The rocks contain a variety of vertebrate remains including a number of dinosaurs, especially Saurischian (lizard-hipped) forms.  The discovery of G. shinyae adds to the diversity of Theropods known, for example a number of carcharodontosaurids are known from this formation (Mapusaurus and Taurovenator), along with several abelisaurids such as Skorpiovenator and Ilokelesia.  There has even been some fossils found that were described as belonging to a giant raptor (Megaraptoran), this dinosaur was named Aoniraptor (A. libertatem) earlier this year, but similarities between the caudal vertebrae found and those now assigned to Gualicho, indicate that the Aoniraptor material may be synonymous with the holotype material of G. shinyae.

There have also be a large number of Sauropod remains associated with this strata.  For example, a number of rebbachisaurids have been described along with several Titanosaurs, including Argentinosaurus.

A Map Showing the Approximate Location of the G. shinyae Quarry

Showing the location of the G. shinyae fossil discovery.

A map showing the approximate location of the fossil discovery (star).

Picture Credit: PLoS One

The black star in the diagram to the left, indicates the approximate location of the G. shinyae quarry.

A spokesperson from Everything Dinosaur commented:

“This new dinosaur discovery adds to the Theropod diversity known from the Late Cretaceous terrestrial strata of the Neuquén Basin, northern Patagonia.  It also reinforces the belief of the close affinities between the Huincul Formation and rocks of a similar age laid down in North Africa.  In addition, with the discovery of a short-armed, two-fingered dinosaur that lived some twenty-five million years or so before the end Cretaceous tyrannosaurids, palaeontologists can perhaps learn why reduced forelimb size was so prevalent in large carnivorous dinosaurs.”

The scientific paper from which this article was compiled is: “An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina”.

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