Quilmesaurus

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Quilmesaurus
Temporal range:
Late Cretaceous, 75–66  Ma
Quilmesaurus and Abelisauridae tibiae.png
The tibia of Quilmesaurus (A-B) compared to that of other abelisaurids
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: Abelisauridae
Clade: Furileusauria
Tribe: Carnotaurini
Genus: Quilmesaurus
Coria, 2001
Type species
Quilmesaurus curriei
Coria, 2001

Quilmesaurus is a genus of carnivorous abelisaurid theropod dinosaur from the Patagonian Upper Cretaceous (Campanian stage) of Argentina. It was a member of Abelisauridae, closely related to genera such as Carnotaurus. [1] The only known remains of this genus are leg bones which share certain similarities to a variety of abelisaurids. However, these bones lack unique features, which may render Quilmesaurus a nomen vanum (more commonly known as a nomen dubium , or "dubious name"). [2]

Contents

Discovery and naming

Skeletal diagram Quilmesaurus Skeletal.svg
Skeletal diagram

During the late 1980s, a field crew from the Universidad Nacional Tucumán, led by Jaime Powell, uncovered forty kilometres south of Roca City, in Río Negro province, southern Argentina, the remains of a theropod near the Salitral Ojo de Agua. In 2001, Rodolfo Aníbal Coria named and described the type species Quilmesaurus curriei. The genus name is derived from the Quilme, a Native American people, and the specific name honours Dr. Philip John Currie, a Canadian theropod specialist. [3]

The holotype and currently only specimen was designated the collection number MPCA-PV-100, in the Museo Provincial "Carlos Ameghino". It consists of the distal (lower or outermost) half of the right femur (thighbone), and a complete right tibia (inner shinbone), collected from the Allen Formation of the Malargüe Group in the Neuquén Basin. These deposits date from the Campanian to Maastrichtian. The specimen came from the fluvial sandstones at the bottom of the Allen Formation. The taxon is notable as it represents one of the youngest records of a non-avian theropod from Patagonia. [3]

Description

The partial femur of Quilmesaurus (A-D) compared to that of Carnotaurus (E-G) Quilmesaurus and Carnotaurus distal femora.png
The partial femur of Quilmesaurus (A-D) compared to that of Carnotaurus (E-G)

The preserved portion of femur is robust and boxy in shape. The rear face of the tip of the bone possessed prominent condyles (joint bumps) for connecting to the tibia (on the inner face of the leg) and fibula (on the outer face of the leg). The lateral condyle (which connected to the fibula) is slightly lower from front-to-back compared to the medial condyle (which connected to the tibia), but it is also wider from side-to-side. An additional finger-like bone spur (an epicondyle) would have also been present on the lateral condyle, although this spur is broken off in the only known Quilmesaurus femur. Just above the medial condyle is a low yet noticeable ridge which juts away from the rest of the bone, towards the midline of the animal's body. This ridge is known as a mesiodistal crest. The area immediately above the condyles possesses a shallow yet wide lowered area known as an extensor groove. Overall the femur is almost identical to that of other abelisaurids. [2]

Life restoration Quilmesaurus curriei.jpg
Life restoration

The proximal (upper or innermost) part of the tibia possesses a myriad of complex features. A large and hatchet-shaped structure known as a cnemial crest points forwards at the proximal portion of the tibia. The tip of the cnemial crest is hooked due to the presence of a downward pointing spur, known as a ventral process. Although Coria (2001) considered a hooked cnemial crest to be unique to Quilmesaurus, [3] Valieri et al. (2007) noted that this structure was also possessed by Aucasaurus and Majungasaurus , as well as the ambiguous abelisaurid Genusaurus . The distal part of the tibia possesses its own projections for connecting to ankle bones, known as malleoli. This part has the form of an asymmetrical triangle when seen from the front, with the massive lateral malleolus projecting further distally than the smaller medial malleolus. This combination of distal tibia features was also once presumed to have been unique to Quilmesaurus. However, Valieri et al. (2007) note that the distal tibia of Rajasaurus was very similar to that of Quilmesaurus. [2]

In 2016, Quilmesaurus was estimated to have measured 5.3 metres (17 ft) in length. This would have made it among the smallest derived abelisaurids, although its legs were proportionally robust like those of Pycnonemosaurus , one of the largest members of the family. [4]

Pathology

Life restoration of abelisaurids from which pathological bones have been described. Quilmesaurus is C. Pathological abelisaurids.png
Life restoration of abelisaurids from which pathological bones have been described. Quilmesaurus is C.

The holotype tibia of Quilmesaurus seems to demonstrate some form of pathology. The exact cause is unclear, but it may have been related to disease or a physiological response to an external force. [5]

Classification

When originally described, Coria could not find a more precise placement for Quilmesaurus than Theropoda. [3] The presence of a notch in the distal articular surface of the tibia was cited by him as evidence of a possible relationship with basal Tetanurae, which would be surprising as Quilmesaurus lived during a time when South American theropod assemblages were dominated by abelisaurids and carcharodontosaurs. Other theropod material has been recovered from within these same strata and has in 2005 also provisionally been referred to the Tetanurae. [6] However, in a 2004 abstract (and later a 2007 full paper), Rubén Juárez Valieri et al. concluded that Quilmesaurus, in view of the hatchet-shaped cnemial crest, was a member of the Abelisauridae. [7] [2]

Unlike members of Megalosauroidea, the tibia of Quilmesaurus does not possess a noticeable anteromedial buttress, and instead it includes a large cnemial crest. Quilmesaurus is also not a coelurosaur due to the distal part of the tibia being asymmetrical in shape as well as having a socket for the astragalus which is lower than that of coelurosaurs. Finally, the shallow and wide (rather than deep and thin) extensor groove excludes Quilmesaurus from Carnosauria, as does the possession of parallel upper and lower edges of the cnemial crest. [2]

However, some features do support its placement within Ceratosauria. These include a pronounced cnemial crest of the tibia and large mesiodistal crest of the femur. The asymmetrical distal part of the tibia and small socket for the astragalus specifically place it within the family Abelisauridae. The preserved bones share features with various abelisaurid taxa throughout the family, although such similarities are widespread and seemingly pop up at random among the taxa, thus making more specific placement difficult. The hook-like shape of the cnemial crest suggests that Quilmesaurus was a member of the subfamily Carnotaurinae, which Sereno (1998) defined to include all abelisaurids closer to Carnotaurus than to Abelisaurus. [2]

Size comparison of Quilmesaurus (far right) with other "carnotaurins" Carnotaurini sizes updated.png
Size comparison of Quilmesaurus (far right) with other "carnotaurins"

However, the validity of Carnotaurinae has been debated. Although Valieri et al. (2007) considered the subfamily to include taxa such as Majungasaurus, Carnotaurus, Aucasaurus, and Rajasaurus, other studies have found different results. Tortosa et al. (2014) found that Carnotaurinae was an invalid group, as very few abelisaurids could actually apply to the definition set forth by Sereno. According to their analysis, Aucasaurus and Carnotaurus were actually closer to Abelisaurus than they were to Majungasaurus and Rajasaurus, thus forcing the latter two taxa to be excluded from the subfamily. Quilmesaurus was retained as close to Aucasaurus and Carnotaurus, although Sereno's name and definition of Carnotaurinae was completely demolished. In its place the tribe Carnotaurini was used, which includes all abelisaurids descended from the last common ancestor of Aucasaurus and Carnotaurus. [8] Tortosa et al. (2014)'s result has largely been supported over that of Valieri et al. (2007). Filippi et al. (2016) created a new clade, Furileusauria, to include abelisaurids more closely related to Carnotaurus than to Ilokelesia , Skorpiovenator , or Majungasaurus. They included Quilmesaurus among the furileusaurians. [1]

Valieri et al. (2007) were unable to establish a single autapomorphy (distinctive or unique trait) of the taxon, concluding that Quilmesaurus were a nomen vanum . [2]

Paleoecology

Quilmesaurus chasing Bonapartesaurus, while an Austroraptor group watches Quilmesaurus hunting Bonapartesaurus version 2.jpg
Quilmesaurus chasing Bonapartesaurus , while an Austroraptor group watches

The Allen Formation is believed to have been a humid coastal environment which gradually transitioned from a freshwater floodplain to marshy estuaries and then shallow lagoons as sea levels rose. A diverse assemblage of aquatic life inhabited the area, including various fish, frogs, and turtles. More recent intervals of the formation even include a few marine reptiles, such as various plesiosaurs including elasmosaurids and polycotylids. [9] Plant life includes palm trees and conifers of the family Podocarpeaceae ("plum pines"), which formed dense forests and wetlands. [10]

Remains of land animals were also common in this formation. An indeterminate rhynchocephalian is known, as well as numerous snake taxa including the madtsoiids Patagoniophis and Alamitophis. [10] Other non-dinosaur animals in the area include the pterosaur Aerotitan [11] and a variety of mammals. [12]

Dinosaur remains recovered from the Allen Formation include a diverse and abundant assortment of titanosaurs ( Saltasaurus, Aeolosaurus, Laplatasaurus, Rocasaurus, etc.) and a hadrosaurid of dubious validity ( Willinakaqe ). [13] Theropods other than Quilmesaurus were also present; they include the large unenlagiine dromaeosaurid Austroraptor , [14] a basal ornithuran bird ( Limenavis ), [15] and a cimolopterygid bird ( Lamarqueavis ). [16] A tooth has been referred to the family Carcharodontosauridae; this tooth is one of the most recent carcharodontosaurid fossils found as more well known members of this family ( Giganotosaurus , Mapusaurus ) lived millions of years earlier in the Cretaceous. [10] Indeterminate nodosaurid remains have also been found at this formation, consisting of vertebrae, osteoderms, a femur, and a tooth. [17]

The Allen Formation is also notable for the high amount of sauropod eggs discovered there. Nesting grounds have been discovered in the bajo de Santa Rosa area of the upper Allen Formation. Some (but not all) of these eggs were designated as the oogenus Sphaerovum . The structure of their eggshells indicate that they were laid in a very damp environment. [10]

See also

Related Research Articles

<i>Carnotaurus</i> Genus of dinosaur from the Late Cretaceous period

Carnotaurus is a genus of theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 72 and 69 million years ago. The only species is Carnotaurus sastrei. Known from a single well-preserved skeleton, it is one of the best-understood theropods from the Southern Hemisphere. The skeleton, found in 1984, was uncovered in the Chubut Province of Argentina from rocks of the La Colonia Formation. Carnotaurus is a derived member of the Abelisauridae, a group of large theropods that occupied the large predatorial niche in the southern landmasses of Gondwana during the late Cretaceous. Within the Abelisauridae, the genus is often considered a member of the Brachyrostra, a clade of short-snouted forms restricted to South America.

<span class="mw-page-title-main">Ceratosauria</span> Extinct clade of dinosaurs

Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with Ceratosaurus than with birds. The oldest known ceratosaur, Saltriovenator, dates to the earliest part of the Jurassic, around 199 million years ago. Ceratosauria includes three major clades: Ceratosauridae, Noasauridae, and Abelisauridae, found primarily in the Southern Hemisphere. Originally, Ceratosauria included the above dinosaurs plus the Late Triassic to Early Jurassic Coelophysoidea and Dilophosauridae, implying a much earlier divergence of ceratosaurs from other theropods. However, most recent studies have shown that coelophysoids and dilophosaurids do not form a natural group with other ceratosaurs, and are excluded from this group.

<i>Abelisaurus</i> Extinct genus of dinosaurs

Abelisaurus is a genus of predatory abelisaurid theropod dinosaur alive during the Late Cretaceous Period (Campanian) of what is now South America. It was a bipedal carnivore that probably reached about 7.4 metres in length, although this is uncertain as it is known from only one partial skull.

<i>Xenotarsosaurus</i> Extinct genus of dinosaurs

Xenotarsosaurus is a genus of abelisaurid theropod dinosaur that lived during the Late Cretaceous of Argentina.

<i>Rugops</i> Genus of dinosaur

Rugops is a monospecific genus of basal abelisaurid theropod dinosaur from Niger that lived during the Late Cretaceous period in what is now the Echkar Formation. The type and only species, Rugops primus, is known only from a partial skull. It was named and described in 2004 by Paul Sereno, Jeffery Wilson and Jack Conrad. Rugops has an estimated length of 4.4–5.3 metres (14–17 ft) and weight of 410 kilograms (900 lb). The top of its skull bears several pits which correlates with overlaying scale and the front of the snout would have had an armour-like dermis.

<span class="mw-page-title-main">Abelisauridae</span> Extinct family of dinosaurs

Abelisauridae is a family of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found on the modern continents of Africa and South America, as well as on the Indian subcontinent and the island of Madagascar. Isolated teeth were found in the Late Jurassic of Portugal, and the Late Cretaceous genera Tarascosaurus and Arcovenator have been described in France. Abelisaurids possibly first appeared during the Jurassic period based on fossil records, and some genera survived until the end of the Mesozoic era, around 66 million years ago.

<i>Aucasaurus</i> Extinct genus of dinosaurs

Aucasaurus is a genus of medium-sized abelisaurid theropod dinosaur from Argentina that lived during the Late Cretaceous 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 to speculate that it was involved in a fight prior to death.

<i>Indosaurus</i> Extinct genus of dinosaurs

Indosaurus is a genus of carnivorous theropod dinosaur that lived in what is now India, about 69 to 66 million years ago during the Maastrichtian division of the Late Cretaceous.

<i>Ekrixinatosaurus</i> Extinct genus of dinosaur

Ekrixinatosaurus is a genus of abelisaurid theropod which lived approximately 100 to 97 million years ago during the Late Cretaceous period. Its fossils have been found in Argentina. Only one species is currently recognized, Ekrixinatosaurus novasi, from which the specific name honors of Dr. Fernando Novas for his contributions to the study of abelisaurid theropods, while the genus name refers to the dynamiting of the holotype specimen. It was a large abelisaur, measuring between 6.5 and 8 m in length and weighing 800 kg (1,800 lb).

Genusaurus is a genus of abelisauroid theropod from the Early Cretaceous. Its fossils were found in France. Genusaurus is believed to have lived during the Albian stage, around 112-100 million years ago.

<i>Pycnonemosaurus</i> Extinct genus of dinosaurs

Pycnonemosaurus is a genus of carnivorous theropod dinosaur that belonged to the family Abelisauridae. It was found in the Upper Cretaceous red conglomerate sandstones of the Cachoeira do Bom Jardim Formation, Mato Grosso, Brazil, and it lived during the late Campanian to early Maastrichtian stage of the Late Cretaceous.

<span class="mw-page-title-main">Carnotaurinae</span> Extinct subfamily of reptiles

Carnotaurinae is a subfamily of the theropod dinosaur family Abelisauridae. As the name suggests, it includes the famous genus Carnotaurus as well as its close relatives from the Cretaceous Period of Argentina and Brazil. The group was first proposed by American paleontologist Paul Sereno in 1998, defined as a clade containing all abelisaurids more closely related to Carnotaurus than to Majungasaurus.

<i>Skorpiovenator</i> Extinct genus of dinosaurs

Skorpiovenator is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Huincul Formation of Argentina. It is one of the most complete and informative abelisaurids yet known, described from a nearly complete and articulated skeleton.

<i>Rahiolisaurus</i> Genus of abelisaurid dinosaur from the Late Cretaceous period

Rahiolisaurus is a genus of abelisaurid theropod dinosaur which existed in India during the Late Cretaceous period. It was described in 2010, based on fossils recovered from the Lameta Formation in the Indian state of Gujarat. These fossils include elements from at least seven different individuals and are believed to have been from the Maastrichtian stage, sometime between 70 and 66 million years ago, making it one of the last non-avian dinosaurs known in the fossil record. Despite representing a variety of different growth stages, all recovered fossils from the locality indicate a single species, the type species Rahiolisaurus gujaratensis.

<i>Bonapartenykus</i> A large alvarezsauroid dinosaur

Bonapartenykus is a monospecific genus of alvarezsauroid dinosaur from Argentina that lived during the Late Cretaceous (Campanian-Maastrichtian) in what is now the upper Allen Formation of the Río Negro Province. The type and only species, Bonapartenykus ultimus, is known from a nearly articulated but partial skeleton that was found in close association to two incomplete eggs and several clusters of eggshells belonging to the oogenus Arriagadoolithus. Bonapartenykus was named in 2012 by Federico L. Agnolin, Jaime E. Powell, Fernando E. Novas and Martin Kundrát. Bonapartenykus has an estimated length of 2.5 m (8.2 ft) and weight of 72 kg (159 lb), making it the largest member of the clade Alvarezsauroidea.

<i>Arcovenator</i> Extinct genus of dinosaurs

Arcovenator is an extinct genus of abelisaurid theropod dinosaurs hailing from the Late Cretaceous of France and possibly Spain. The type and only described species is Arcovenator escotae.

<span class="mw-page-title-main">Majungasaurinae</span> Extinct subfamily of reptiles

Majungasaurinae is a subfamily of large carnivorous theropods from the Upper Cretaceous, found in Madagascar, India, and France. It is a subgroup within the theropod family Abelisauridae, a Gondwanan clade known for their thick and often horned skulls and vestigial arms. The two subfamilies of Abelisauridae are Carnotaurinae, best known from the South American Carnotaurus, and Majungasaurinae, consisting of Madagascar’s Majungasaurus and its closest relatives. Their ancestors emerged in the Middle Jurassic, and the clade lasted until the Upper Cretaceous.

<i>Viavenator</i> Extinct genus of dinosaurs

Viavenator is a genus of carnivorous abelisaurid theropod dinosaur discovered in Argentina's Bajo de la Carpa Formation. It coexisted with the megaraptoran Tratayenia rosalesi.

<i>Bonapartesaurus</i> Extinct genus of dinosaurs

Bonapartesaurus is an extinct genus of herbivorous ornithopod dinosaur belonging to Hadrosauridae, which lived in the area of modern Argentina during the Campanian and Maastrichtian stages of the Late Cretaceous.

Tralkasaurus is a genus of abelisaurid dinosaur from the Huincul Formation from Río Negro Province in Argentina. The type and only species is Tralkasaurus cuyi, named in 2020 by Mauricio Cerroni and colleagues based on an incomplete skeleton. A medium-sized abelisaurid, Tralkasaurus exhibits a conflicting blend of characteristics found among the early-diverging abelisauroids with others that characterize the highly specialized clade Brachyrostra, and thus its position within the clade is poorly-resolved.

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