''Meraxes'' is a genus of

carcharodontosaurid Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

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 ...

dinosaur from the Late Cretaceous

Huincul Formation The Huincul Formation is a geologic formation of Late Cretaceous ( Early Cenomanian to Late Turonian) age of the Neuquén Basin that outcrops in the Mendoza, Río Negro and Neuquén Provinces of northern Patagonia, Argentina.

of Argentine

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

. The genus contains a single species, ''Meraxes gigas''.

Discovery and naming

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

of ''Meraxes'', previously called the "Campanas carcharodontosaurid", MMCh-PV 65, was discovered in 2012. Known bones include a nearly complete

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectorali ...

and

pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The p ...

elements, partial forelimbs, complete hindlimbs, fragmentary

ribs The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

and

cervical In anatomy, cervical is an adjective that has two meanings: # of or pertaining to any neck. # of or pertaining to the female cervix: i.e., the ''neck'' of the uterus. *Commonly used medical phrases involving the neck are **cervical collar **cerv ...

and

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

vertebrae, a sacrum, and several complete caudal vertebrae. It has the most complete carcharodontosaurid skeleton known from the Southern Hemisphere. ''Meraxes gigas'' was described in 2022 by Canale ''et al''. based on these remains. The generic name, "''Meraxes''", honors a dragon from the

George R.R. Martin George Raymond Richard Martin (born George Raymond Martin; September 20, 1948), also known as GRRM, is an American novelist, screenwriter, television producer and short story writer. He is the author of the series of epic fantasy novels '' A So ...

fantasy novel series, '' A Song of Ice and Fire''. The specific name, "''gigas''", is derived from a

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word meaning "giant", in reference to its large size.

Description

''Meraxes'' was a very large theropod, weighing approximately . Its

alone is long, rivalling that of ''

Acrocanthosaurus ''Acrocanthosaurus'' ( ; ) is a genus of carcharodontosaurid dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous, from 113 to 110 million years ago. Like most dinosaur genera, ' ...

'' which has a skull length of . The shapes and proportions of various bones (i.e. skull, scapula, metacarpals, ischial shaft, foot, etc.) indicate that ''Meraxes'' and ''Acrocanthosaurus'' had similar proportions and body size. It also possessed reduced forelimbs, an instance of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

that occurred independently in four different lineages:

Carcharodontosauridae Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

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 fou ...

Tyrannosauridae Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...

, and Alvarezsauridae. Osteohistological analysis of the holotype suggests the individual could have been up to 53 years old when it died, having reached skeletal maturity approximately 4 years prior to its death, making it the longest-lived non-avian theropod currently known. ''Meraxes'' was also determined to have grown to large size by extending its growth period ( hypermorphosis), rather than increasing its relative growth rate (

acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...

) through development as in ''

Tyrannosaurus ''Tyrannosaurus'' is a genus of large theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosaurus'' live ...

'', to which it was compared.

Classification

''Meraxes'' represents the earliest diverging member of the tribe

Giganotosaurini Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

within the Carcharodontosauridae. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below displays the results of the

phylogenetic analysis 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 ...

by Canale ''et al.''

Paleoenvironment

The fossil remains of ''Meraxes'' were recovered from the

. A substantial number of taxa are known to have inhabited this paleoenvironment. The theropods of the area are represented by the paravian ''

Overoraptor ''Overoraptor'' (meaning "piebald thief") is a genus of paravian theropod dinosaurs, which was closely related to ''Rahonavis'', from the Late Cretaceous (Cenomanian) Huincul Formation of Gondwana, present-day Argentina. It includes one species ...

'', the elaphrosaurine '' Huinculsaurus'', the abelisaurs ''

Skorpiovenator ''Skorpiovenator'' ("scorpion hunter") is a genus of abelisaurid theropod dinosaur from the Late Cretaceous (Cenomanian to Turonian) Huincul Formation of Argentina. It is one of the most complete and informative abelisaurids yet known, describe ...

'', ''

Tralkasaurus ''Tralkasaurus'' (meaning "thunder lizard") 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 ...

'', and '' Ilokelesia'', the fellow giant carcharodontosaurid ''Mapusaurus'', and the megaraptoran ''

Aoniraptor ''Aoniraptor'' is a megaraptoran theropod from the Late Cretaceous of Argentina (Huincul Formation). Discovery and naming The holotype, MPCA-Pv 804/1 to 804/25, which consists of the last sacral vertebra, six proximal caudal vertebrae, four mid ...

''. However, ''Meraxes'' was found in an older rock layer than ''Mapusaurus'', so they probably did not coexist. The herbivores of the area are represented by the rebbachisaurid sauropods '' Cathartesaura'' and '' Limaysaurus'', the titanosaurs ''

Argentinosaurus ''Argentinosaurus'' is a genus of giant sauropod dinosaur that lived during the Late Cretaceous period in what is now Argentina. Although it is only known from fragmentary remains, ''Argentinosaurus'' is one of the largest known land animal ...

'' and ''

Choconsaurus ''Choconsaurus'' is an extinct genus of herbivorous sauropod dinosaur belonging to the group Titanosauriformes, which lived in the area of present-day Argentina at the end of the Cretaceous. Discovery and naming The holotype (specimen MMCh-P ...

'', and indeterminate

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 ...

s.Calvo, J. O. and Salgado, L. (1995).
''Rebbachisaurus tessonei'' sp. nov. A new sauropod from the Albian-Cenomanian of Argentina; new evidence on the origin of the Diplodocidae
" ''Gaia'', 11: 13-33.

References

{{Taxonbar, from= Q112966897, from2= Q112969374 Carcharodontosaurids Cenomanian life Cretaceous Argentina Fossil taxa described in 2022 Fossils of Argentina Huincul Formation Late Cretaceous dinosaurs of South America Turonian life