''Chucarosaurus'' (meaning "indomitable reptile") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of

titanosaurian 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 ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from 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 ...

(middle

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

–lower

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...

) Huincul Formation of

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 ...

. The genus contains a single species, ''C. diripienda'', known from various limb bones.

Discovery and naming

The ''Chucarosaurus''

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 several ...

specimen, MPCA PV 820, was discovered in sediments of the Huincul Formation, dated to the middle

–lower

ages of the 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 ...

period, at Pueblo Blanco Natural Reserve in Río Negro Province, Argentina. The specimen consists of a complete left

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, partial left

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

, complete left metacarpal II, left

ischium The ischium () form ...

, partial left

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

and

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...

, partial right

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

, and partial indeterminate

metapodial Metapodials are long bones of the hand (metacarpals) and feet (metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. ...

, all of which belong to one individual. An additional specimen (MPCA PV 821), consisting of a left femur and tibia, was also referred as a paratype. In 2023, Agnolin ''et al''. described ''Chucarosaurus diripienda'', a new genus and species of colossosaurian titanosaurs, based on these fossil remains. The generic name, "''Chucarosaurus''", combines "chucaro", a Quechua word meaning "hard and indomitable animal" with the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word "saurus", meaning "reptile". The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, "''diripienda''", is derived from a Latin word meaning "scrambled".

Description

''Chucarosaurus'' was a large, slender-limbed titanosaur. Its

was roughly long, somewhat smaller than the estimated length of the femur of '' Argentinosaurus''. The forelimb was shorter than the hind limb, with a humerus 78% the length of the femur, as is typical of titanosaurs but unlike some basal titanosauriforms such as

brachiosaurids The Brachiosauridae ("arm lizards", from Greek ''brachion'' (βραχίων) = "arm" and ''sauros'' = "lizard") are a family or clade of herbivorous, quadrupedal sauropod dinosaurs. Brachiosaurids had long necks that enabled them to access the le ...

. As in other colossosaurs, the deltopectoral crest of the humerus was thickened in its distal half. The

ischium The ischium () form ...

has a shorter, more robust iliac peduncle than in other titanosaurs.

Classification

Agnolin ''et al''. (2023) recovered ''Chucarosaurus'' as a colossosaurian member of the Titanosauria, as the

sister taxon 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 ...

to a clade formed by ''

Notocolossus ''Notocolossus'' is a genus of titanosaurian sauropod dinosaur from late Cretaceous strata of Mendoza Province, Argentina. Discovery and naming A fossil of a large sauropod was discovered by the Argentine paleontologist Dr. Bernardo Javier ...

'' and the

Lognkosauria Lognkosauria is a clade of giant long-necked sauropod dinosaurs within the clade Titanosauria. It includes some of the largest and heaviest dinosaurs known. Description Lognkosaurians can be distinguished from other titanosaurs by the wide and u ...

. The results of their phylogenetic analyses are shown in the cladogram below:

Palaeoenvironment

''Chucarosaurus'' is known from the Late Cretaceous Huincul Formation of Río Negro Province, Argentina. Many dinosaurs, including fellow titanosaurs ('' Argentinosaurus'' 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 ...

''), rebbachisaurids (''

Cathartesaura ''Cathartesaura'' is a genus of rebbachisaurid sauropod dinosaur hailing from the Late Cretaceous strata of the Huincul Formation, at the "La Buitrera" locality, in the Neuquén Basin of Río Negro Province, Argentina. The fossil remains, describ ...

'' and ''

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 ( ...

''), carcharodontosaurids ('' Mapusaurus'', ''

Meraxes ''Meraxes'' is a genus of carcharodontosaurid theropod dinosaur from the Late Cretaceous Huincul Formation of Argentine Patagonia. The genus contains a single species, ''Meraxes gigas''. Discovery and naming The holotype of ''Meraxes'', prev ...

'', and ''

Taurovenator ''Taurovenator'' is a medium-sized carcharodontosaurid theropod from the late Cretaceous of Argentina. Discovered by Matias Motta in 2005 and formally described in 2016, it is represented by an isolated right postorbital. Etymology The ''tauro ...

''), a 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 ...

''), abelisaurids ('' Skorpiovenator'', '' Tralkasaurus'', and ''

Ilokelesia ''Ilokelesia'' is an extinct genus of abelisaurid theropod,Coria, R.A.; Salgado, L. & Calvo, J.O. (1991) "Primeros restos de dinosaurios Theropoda del Miembro Huincul, Formación Río Limay (Cretácico Tardío Presenoniano), Neuquén, Argentina." ...

''), an elaphrosaurine (''

Huinculsaurus ''Huinculsaurus'' (meaning "Huincul Formation lizard") is a genus of noasaurid dinosaur from the Huincul Formation in Neuquén Province, Argentina. The type and only species is ''Huinculsaurus montesi''. It was probably around when fully grown, ...

''), a paravian ('' Overoraptor''), and the unusual avetheropod ''

Gualicho ''Gualicho'' (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off from the superco ...

'' have also been named from the formation. Remains of unenlagiids, iguanodonts, and elasmarian ornithopods are also known.

References

{{Taxonbar, from=Q116621259 Titanosaurs Fossil taxa described in 2023 Late Cretaceous dinosaurs of South America Fossils of Argentina Huincul Formation