''Ekrixinatosaurus'' ('explosion-born reptile') is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
abelisaurid
Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
which lived approximately 100 to 97
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
during the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
period. Its fossils have been found in
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. Only one species is currently recognized, ''Ekrixinatosaurus novasi'', from which the specific name honors of Dr.
Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina. for his contributions to the study of abelisaurid theropods. It was a large abelisaur, measuring between in length and weighing .
Discovery and naming
The
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
, ''Ekrixinatosaurus novasi'', was first described in 2004 by Argentinian
paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Jorge Calvo, and Chilean paleontologists David Rubilar-Rogers and Karen Moreno.
The fossils were found dispersed over an area of 15m in the
Candeleros Formation
The Candeleros Formation (formerly known as the Candeleros Member of the "Río Limay Formation") is a geologic formation that crops out in the Río Negro, Neuquén, and Mendoza provinces of northern Patagonia, Argentina. It is the oldest formati ...
, a geologic formation that outcrops in
Río Negro,
Neuquén
Neuquén (; arn, Nehuenken) is the capital city of the Argentine province of Neuquén and of the Confluencia Department, located in the east of the province. It occupies a strip of land west of the confluence of the Limay and Neuquén rivers w ...
, and
Mendoza provinces of Argentina. This formation dates from 100-97 mya.,
and consists of red beds where other famous vertebrate animals have been discovered, such as ''
Giganotosaurus
''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 ...
'', ''
Rebbachisaurus
''Rebbachisaurus'' (meaning "Khebbash, Aït Rebbach lizard") is a genus of sauropod dinosaur of the superfamily Diplodocoidea, that lived during the Late Cretaceous period in Africa and possibly also South America about 99-97 million years ago. R ...
'', and ''
Andesaurus
''Andesaurus'' ( ; "Andes lizard") is a genus of basal titanosaurian sauropod dinosaur which existed during the middle of the Cretaceous Period in South America. Like most sauropods, belonging to one of the largest animals ever to walk the Eart ...
''. The discovery occurred due to excavations for building a gas pipeline conducted by Gasoducto del Pacífico Company in Bajo del Añelo.
Before the discovery of ''Ekrixinatosaurus'', ''
Carnotaurus sastrei
''Carnotaurus'' (; ) is a genus of theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 71 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a single well-p ...
'' and ''
Aucasaurus garridoi
''Aucasaurus'' is a genus of medium-sized abelisaurid theropod dinosaur from Argentina that lived during the Late Cretaceous (Santonian to Campanian stage) of the Anacleto Formation. It was smaller than the related ''Carnotaurus'', although more ...
'' were the most complete specimens of the
abelisauridae
Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
family.
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.
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.
Description
![Ekrixinatosaurus novasi scale diagram](https://upload.wikimedia.org/wikipedia/commons/2/2e/Ekrixinatosaurus_novasi_scale_diagram.png)
''Ekrixinatosaurus novasi'' is a large
abelisaurid
Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
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.
The only known specimen was previously estimated between in length and in body mass,
and some suggested that this specimen actually represented the largest abelisaurid yet known at in length, surpassing the type of ''
Carnotaurus
''Carnotaurus'' (; ) is a genus of theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 71 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a single well-p ...
''.
However, it was later noted by other researchers that the latter length estimate of 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.
Skull
![Ekrixinatosaurus novasi skull diagram](https://upload.wikimedia.org/wikipedia/commons/7/70/Ekrixinatosaurus_novasi_skull_diagram.png)
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.
The skull is estimated to be approximately 83 cm long based on comparisons with ''
Carnotaurus
''Carnotaurus'' (; ) is a genus of theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 71 and 69 million years ago. The only species is ''Carnotaurus sastrei''. Known from a single well-p ...
'' and ''
Majungasaurus
''Majungasaurus'' (; ) is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period (geology), Period, making it one of the last known non-avian dinosaurs that went ex ...
'', and while ''
Abelisaurus
''Abelisaurus'' (; "Abel's lizard") 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 in length, althou ...
'' does not have a complete maxilla its preserved size is similar to that of ''Ekrixinatosaurus''.
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.
The maxilla was short and contained 16 alveoli, some with short teeth that were flattened laterally with anterior and posterior serrations.
The maxilla of ''Ekrixinatosaurus'' also exhibits a dorsally projected ascending ramus and a short rostral ramus, suggesting a relatively high skull.
Classification
![Ekrixinatosaurus novasi by Henrique Paes](https://upload.wikimedia.org/wikipedia/commons/c/c9/Ekrixinatosaurus_novasi_by_Henrique_Paes.png)
In 2004, ''Ekrixinatosaurus'' was placed in the
Abelisauridae
Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
. The article by Calvo ''et al.'' in 2004, also contained a preliminary
cladistic
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
analysis of the
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
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
Carnotaurini is a tribe of the theropod dinosaur family Abelisauridae from the Late Cretaceous period of Patagonia. It includes the dinosaurs ''Carnotaurus sastrei''; the type species, ''Aucasaurus garridoi'', and ''Abelisaurus comahuensis''. Thi ...
than to ''
Ceratosaurus
''Ceratosaurus'' (from Ancient Greek, Greek κέρας/κέρατος, ' meaning "horn" and wikt:σαῦρος, σαῦρος ' meaning "lizard") was a carnivorous Theropoda, theropod dinosaur in the Late Jurassic Period (geology), period (Kim ...
''.
In 2008, a study recovered it as the
sister species
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and t ...
of ''Skorpiovenator''.
Paleoecology
''Ekrixinatosaurus'' was found in the red beds of the
Candeleros Formation
The Candeleros Formation (formerly known as the Candeleros Member of the "Río Limay Formation") is a geologic formation that crops out in the Río Negro, Neuquén, and Mendoza provinces of northern Patagonia, Argentina. It is the oldest formati ...
, which has yielded a wide variety of vertebrates. It shared its environment with the
titanosauria
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
n
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
''
Andesaurus
''Andesaurus'' ( ; "Andes lizard") is a genus of basal titanosaurian sauropod dinosaur which existed during the middle of the Cretaceous Period in South America. Like most sauropods, belonging to one of the largest animals ever to walk the Eart ...
'' and the
rebbachisaurid
Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, North America, Europe and possibly Central Asia.
Taxonomy
In 1990 sauropod specialist Jack McIntosh included t ...
sauropods ''
Limaysaurus
''Limaysaurus'' ("Limay lizard") is a genus represented by a single species of rebbachisaurid sauropod dinosaurs, which lived during the mid-Cretaceous period, about 99.6 to 97 million years ago, in the Cenomanian, in what is now South America ( ...
'' and ''
Nopcsaspondylus
''Nopcsaspondylus'' (meaning " Nopcsa's vertebra", in reference to the original describer) is a genus of rebbachisaurid sauropod dinosaur (a type of large, long-necked quadrupedal herbivorous dinosaur) from the Cenomanian-age (Upper Cretaceous) C ...
''.
Iguanodont
Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', ''Tenontosaurus'', and the hadrosaurids or "duck-bil ...
ornithischian
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
remains have reportedly also been found. The
carcharodontosaurid
Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...
''
Giganotosaurus
''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 ...
'' was possibly the
apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
. Smaller predators also inhabited the area, including the
dromaeosaurid
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
''
Buitreraptor
''Buitreraptor'' (meaning "La Buitrera seizer") is a genus of dromaeosaurid dinosaurs that lived during the Late Cretaceous of Argentina at the Candeleros Formation. ''Buitreraptor'' was described in 2005 and the type species is ''Buitreraptor go ...
'', the
alvarezsauroid
Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez ...
''
Alnashetri
''Alnashetri'' is an extinct genus of alvarezsaurid coelurosaurian theropod dinosaur known from the early Late Cretaceous ( Cenomanian stage) of La Buitrera, Río Negro Province, Argentina. It contains one known species, ''Alnashetri cerropolici ...
'', and the basal
coelurosaurian ''
Bicentenaria''. Other primitive reptiles lived in the area, such as the primitive snake ''
Najash
''Najash'' is an extinct genus of basal snake from the Late Cretaceous Candeleros Formation of Patagonia. Like a number of other Cretaceous and living snakes it retained hindlimbs, but ''Najash'' is unusual in having well-developed legs that e ...
'', the crocodile ''
Araripesuchus
''Araripesuchus'' is a genus of extinct crocodyliform that existed during the Cretaceous period of the late Mesozoic era some 125 to 66 million years ago. Six species of ''Araripesuchus'' are currently known. They are generally considered to be n ...
'', along with turtles, fish, pipid frogs, and mammals.
Pterosaur
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
s also lived in the area, as evidenced by pterosaur tracks.
A wide variety of dinosaur trackways have also been found in the
Candeleros Formation
The Candeleros Formation (formerly known as the Candeleros Member of the "Río Limay Formation") is a geologic formation that crops out in the Río Negro, Neuquén, and Mendoza provinces of northern Patagonia, Argentina. It is the oldest formati ...
, suggesting significant activity in the area.
Recent studies on
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
n theropods have interpreted abelisauroids as modest and medium-sized dinosaurs that co-occurred with giant
carcharodontosaurid
Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...
s during the Early and early Late
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
. 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.
However, it has been observed that both ''
Giganotosaurus
''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 ...
'' 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).
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
The Kerguelen Plateau (, ), also known as the Kerguelen–Heard Plateau, is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about to the southwest of Australia and is ...
that formed prior to the separation of Africa and South America.
See also
*
Timeline of ceratosaur research
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 ...
References
{{Portal bar, Dinosaurs, Cretaceous
Brachyrostrans
Cenomanian life
Late Cretaceous dinosaurs of South America
Cretaceous Argentina
Fossils of Argentina
Candeleros Formation
Fossil taxa described in 2004