Ekrixinatosaurus

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Ekrixinatosaurus
Temporal range: Cenomanian
~98  Ma
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Ekrixinatosaurus novasi skeletal diagram.png
Skeletal diagram
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: Abelisauridae
Clade: Brachyrostra
Genus: Ekrixinatosaurus
Calvo et al. 2004
Type species
Ekrixinatosaurus novasi
Calvo et al. 2004

Ekrixinatosaurus ('explosion-born reptile') 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 (21 and 26 ft) in length and weighing 800 kg (1,800 lb).

Contents

Discovery and naming

The type species, Ekrixinatosaurus novasi, was first described in 2004 by Argentinian paleontologist Jorge Calvo, and Chilean paleontologists David Rubilar-Rogers and Karen Moreno. [1] The fossils were found dispersed over an area of 15 m2 in the Candeleros Formation, a geologic formation that outcrops in Río Negro, Neuquén and Mendoza provinces of Argentina. This formation dates from 100 to 97 mya, [2] and consists of red beds where other famous vertebrate animals have been discovered, such as Giganotosaurus , Rebbachisaurus and Andesaurus . The discovery occurred due to excavations for building a gas pipeline conducted by Gasoducto del Pacífico Company in Bajo del Añelo. [1]

Before the discovery of Ekrixinatosaurus, Carnotaurus sastrei and Aucasaurus garridoi were the most complete specimens of the abelisauridae family. [1] The remains of Ekrixinatosaurus helped fill in more information about abelisaur anatomy as it contained portions of the skeleton that were previously unknown, unpublished, or poorly preserved in other specimens. [1] The holotype skeleton (MUCPv-294) was well preserved yet disarticulated. It contained elements including a left and partial right maxillae; basicranium; both dentaries; teeth; cervical, a dorsal, sacral and caudal vertebrae; haemal arches; ribs; ilia, pubis and proximal ischia; left and distal end of right femur; left tibia; left astragalus and calcaneum; proximal end of left fibula and right tibia; metatarsals; phalanges; and a pedal ungual. [1]

Description

Ekrixinatosaurus compared in size to a human Ekrixinatosaurus novasi scale diagram.png
Ekrixinatosaurus compared in size to a human

Ekrixinatosaurus novasi is a large abelisaurid with a relatively large head and robust limbs. The combination of characteristics including a large skull, prominent supraorbital ridge above the dorsal aspect of the orbit, anteroposteriorly compressed cervical vertebrae, and robust, proportionally short hindlimbs with a tibia shorter than femur suggests that this was a massive animal with a great capacity to sustain injuries during intraspecific or interspecific combat. [3] The only known specimen was previously estimated between 6.5 and 8 m (21 and 26 ft) in length and 800 kg (1,800 lb) in body mass, [1] [4] and some suggested that this specimen actually represented the largest abelisaurid yet known at 10 to 11 m (33 to 36 ft) in length, surpassing the type of Carnotaurus . [3] However, it was later noted by other researchers that the latter length estimate of 10 to 11 m (33 to 36 ft) was based only on the absolute size of the skull, ignoring that limb bone comparisons clearly show Carnotaurus was larger, and thus Carnotaurus was larger than Ekrixinatosaurus but with a proportionally smaller head. [5] [6]

Skull

Skull diagram Ekrixinatosaurus novasi skull diagram.png
Skull diagram

The skull of Ekrixinatosaurus was boxy and proportionally shorter and deeper than most other large carnivorous dinosaurs. The jaws also curved upward, a trait shared with some other abelisaurs. [7] The skull is estimated to be approximately 83 cm long based on comparisons with Carnotaurus and Majungasaurus , and while Abelisaurus does not have a complete maxilla its preserved size is similar to that of Ekrixinatosaurus. [3] As in other abelisaurids, the facial bones, especially the nasal bones, were sculptured with numerous small holes and spikes. In life, a wrinkled and possibly keratinous skin would have covered these bones. [7] The maxilla was short and contained 16 alveoli, some with short teeth that were flattened laterally with anterior and posterior serrations. [1] The maxilla of Ekrixinatosaurus also exhibits a dorsally projected ascending ramus and a short rostral ramus, suggesting a relatively high skull. [3]

Classification

Restoration Ekrixinatosaurus novasi by Henrique Paes.png
Restoration

In 2004, Ekrixinatosaurus was placed in the Abelisauridae. The article by Calvo et al. in 2004, also contained a preliminary cladistic analysis of the phylogenetic relationships between Ekrixinatosaurus and those abelisaurids of which at the time relatively complete skeletons were known, finding it to be more closely related to Carnotaurini than to Ceratosaurus . [1]

In 2008, a study recovered it as the sister species of Skorpiovenator.

  Carnotaurinae  

Paleoecology

Restoration of Ekrixinatosaurus (front right) with contemporary dinosaurs Hunting season in Argentina.jpg
Restoration of Ekrixinatosaurus (front right) with contemporary dinosaurs

Ekrixinatosaurus was found in the red beds of the Candeleros Formation, which has yielded a wide variety of vertebrates. It shared its environment with the titanosaurian sauropod Andesaurus and the rebbachisaurid sauropods Limaysaurus and Nopcsaspondylus . Iguanodont ornithischian remains have reportedly also been found. The carcharodontosaurid Giganotosaurus was possibly the apex predator. Smaller predators also inhabited the area, including the dromaeosaurid Buitreraptor , the alvarezsauroid Alnashetri , and the basal coelurosaurian Bicentenaria . Other primitive reptiles lived in the area, such as the primitive snake Najash , the crocodile Araripesuchus , along with turtles, fish, pipid frogs and mammals. Pterosaurs also lived in the area, as evidenced by pterosaur tracks. [2] A wide variety of dinosaur trackways have also been found in the Candeleros Formation, suggesting significant activity in the area. [1]

Recent studies on Gondwanan theropods have interpreted abelisauroids as modest and medium-sized dinosaurs that co-occurred with giant carcharodontosaurids during the Early and early Late Cretaceous. It has been hypothesized that it was only after extinction of these carcharodontosaurids that abelisaurids were able to diversify into more robust forms that occupied the niche of top predators of their ecosystems. [3] However, it has been observed that both Giganotosaurus and Ekrixinatosaurus were among the largest of their respective clades yet existed at the same time, which refutes this hypothesis. Both these animals occupied the role of the largest carnivores; however, it is uncertain whether they played different ecological roles (such as active predation vs. scavenging). [3] In addition, the known distribution of abelisaurids in South America, Madagascar and India brings the hypothesis of a dispersion route between these areas by a terrestrial bridge called the Kerguelen Plateau that formed prior to the separation of Africa and South America. [1]

See also

Related Research Articles

<i>Giganotosaurus</i> Carcharodontosaurid dinosaur genus from the late Cretaceous period

Giganotosaurus is a genus of theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period, approximately 99.6 to 95 million years ago. The holotype specimen was discovered in the Candeleros Formation of Patagonia in 1993 and is almost 70% complete. The animal was named Giganotosaurus carolinii in 1995; the genus name translates to "giant southern lizard", and the specific name honors the discoverer, Ruben Carolini. A dentary bone, a tooth, and some tracks, discovered before the holotype, were later assigned to this animal. The genus attracted much interest and became part of a scientific debate about the maximum sizes of theropod dinosaurs.

<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.

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

Carcharodontosauridae is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae as a family, which, in modern paleontology, indicates a clade within Carnosauria. Carcharodontosaurids include some of the largest land predators ever known: Giganotosaurus, Mapusaurus, Carcharodontosaurus, and Tyrannotitan all rivaled Tyrannosaurus in size. Estimates give a maximum weight of 8–10 metric tons for the largest carcharodontosaurids, while the smallest carcharodontosaurids were estimated to have weighed at least 500 kilograms (1,100 lb).

<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, Arcovenator and Caletodraco 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>Megaraptor</i> Extinct genus of dinosaurs

Megaraptor is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America. Initially thought to have been a giant dromaeosaur-like coelurosaur, it was classified as a neovenatorid allosauroid in previous phylogenies, but more recent phylogeny and discoveries of related megaraptoran genera has placed it as either a basal tyrannosauroid or a basal coelurosaur with some studies still considering it a neovenatorid.

<i>Ilokelesia</i> Extinct genus of reptiles

Ilokelesia is an extinct genus of abelisaurid theropod, preserved in the layers of the earliest Late Cretaceous of the Huincul Formation, Neuquén Group, located near Plaza Huincul, Neuquén Province, Argentina. The specimen, consisting of very fragmentary elements of the skull and the axial and appendicular skeleton, was described by Rodolfo Coria and Leonardo Salgado in late 1998.

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

Quilmesaurus is a genus of carnivorous abelisaurid theropod dinosaur from the Patagonian Upper Cretaceous of Argentina. It was a member of Abelisauridae, closely related to genera such as Carnotaurus. 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.

<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.

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

Brachyrostra is a clade within the theropod dinosaur family Abelisauridae. It includes the famous genera Carnotaurus, Abelisaurus, Aucasaurus as well as their close relatives from the Cretaceous Period of Argentina and Brazil plus Caletodraco from France. The group was first proposed in an analysis conducted by Juan Canale and colleagues in 2008. They found that all South American abelisaurids described up to that point grouped together as a sub-clade of Abelisauridae, which they named based on the relatively unusual shape of their skulls. They defined the clade Brachyrostra as "all the abelisaurids more closely related to Carnotaurus sastrei than to Majungasaurus crenatissimus."

<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.

<span class="mw-page-title-main">Timeline of ceratosaur research</span>

This timeline of ceratosaur research is a chronological listing of events in the history of paleontology focused on the ceratosaurs, a group of relatively primitive, often horned, predatory theropod dinosaurs that became the apex predators of the southern hemisphere during the Late Cretaceous. The nature and taxonomic composition of the Ceratosauria has been controversial since the group was first distinguished in the late 19th century. In 1884 Othniel Charles Marsh described the new genus and species Ceratosaurus nasicornis from the Late Jurassic Morrison Formation of the western United States. He felt that it belonged in a new family that he called the Ceratosauridae. He created the new taxon Ceratosauria to include both the Ceratosauridae and the ostrich-like ornithomimids. The idea of the Ceratosauria was soon contested, however. Later that same decade both Lydekker and Marsh's hated rival Edward Drinker Cope argued that the taxon was invalid.

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.

Kaikaifilusaurus is an extinct genus of rhynchocephalians in the family Sphenodontidae from the Late Cretaceous of South America. Fossils of the genus were found in Cenomanian sediments of the Candeleros Formation and Turonian layers of the Huincul Formation, both of the Neuquén Basin and the Albian strata of the Cerro Barcino Formation in the Cañadón Asfalto Basin, all in Patagonia, Argentina. The genus contains two species, K. minimus and the type species K. calvoi.

<i>Meraxes</i> Genus of carcharodontosaurid dinosaurs

Meraxes is a genus of large carcharodontosaurid theropod dinosaur from the Late Cretaceous Huincul Formation of Patagonia, Argentina. The genus contains a single species, Meraxes gigas.

References

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  2. 1 2 Leanza, Héctor A.; Apesteguı́a, Sebastián; Novas, Fernando E.; de la Fuente, Marcelo S. (2004). "Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages". Cretaceous Research. 25 (1): 61–87. Bibcode:2004CrRes..25...61L. doi:10.1016/j.cretres.2003.10.005.
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