Chakisaurus

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Chakisaurus
Temporal range: Late Cretaceous, (CenomanianTuronian)
Chakisaurus LMR.png
Life Restoration of an adult Chakisaurus along with two juvenile individuals.
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Neornithischia
Clade: Ornithopoda
Clade: Elasmaria
Genus: Chakisaurus
Species:
C. nekul
Binomial name
Chakisaurus nekul
Alvarez Nogueira et al., 2024

Chakisaurus (meaning "elder guanaco lizard") is an extinct genus of elasmarian ornithopod dinosaur from the Late Cretaceous Huincul Formation of Argentina. The genus contains a single species, C. nekul, known from multiple partial skeletons belonging to individuals of different ages. Chakisaurus represents the first ornithischian species to be named from the Huincul Formation.

Contents

Discovery and naming

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Chakisaurus type locality at Pueblo Blanco Natural Reserve, Argentina

The Chakisaurus fossil material was discovered in sediments of the Huincul Formation in Pueblo Blanco Natural Reserve (previously known as the Violante Farm locality) near Ezequiel Ramos-Mexía Lake in Río Negro Province, Argentina. The holotype specimen, MPCA Pv 816, consists of several partial dorsal vertebrae, a partial sacrum, twelve caudal vertebrae, an incomplete haemal arch, partial left femur and fibula, partial right tibia and calcaneus, and two toe bones from the fourth digit. Three additional paratype specimens were also assigned to Chakisaurus, found in a group about 500 metres (1,600 ft). The first is MPCA Pv 822, which belongs to a juvenile individual, including five dorsal vertebral centra, a left humerus, and the bottoms of both femora. The second is MPCA Pv 823, another juvenile individual consisting of the top of a right ulna. The third is MPCA Pv 813, which includes eight dorsal vertebral centra, two partial ribs, two partial haemal arches, the bottom of a right radius, a toe bone of digit four, and a toe claw of digit two or four. An additional cervical vertebra (possibly the fourth), MPCN Pv 846, was also referred to Chakisaurus. [1]

In 2024, Alvarez Nogueira et al. described Chakisaurus nekul as a new genus and species of ornithopod based on these fossil remains. The generic name, "Chakisaurus", combines "Chaki", an Aonikenk word meaning "elder guanaco"—, referring to the species Lama guanicoe —with the Greek "σαῦρος" ("sauros"), meaning "lizard". The specific name, "nekul", is a Mapudungun word meaning "swift". [1]

Chakisaurus represents the tenth basal ornithopod named from South America. [1]

Description

Chakisaurus has been described as a "medium-sized" elasmarian ornithopod, similar in size to taxa such as Anabisetia , Notohypsilophodon and Trinisaura , but smaller than taxa such as Talenkauen , Mahuidacursor , and Isasicursor . Analysis of the forelimb bones preserved for the species finds no adaptations towards some level of quadrupedal locomotion, suggesting that some other elasmarians developed these traits independently. [1]

When the anterior caudal vertebrae were articulated, this likely resulted in a protonic posture, with the base of the tail curving downward. This feature has only otherwise been observed in titanosaurs, including the aeolosaurin Arrudatitan . Like other elasmarians, the tail shares similar adaptations towards cursoriality as with some coelurosaur theropods. [1] [2] [3]

Classification

In their phylogenetic analyses, Alvarez Nogueira et al. (2024) recovered Chakisaurus as an elasmarian ornithopod within the iguanodontian clade Dryomorpha. They note that due to the fragmentary nature of the Chakisaurus fossil material, their tree was not well-defined. Their results are shown in the cladogram below: [1]

Palaeoenvironment

Size of several dinosaurs from the Huincul Formation compared to a human Huincul Formation Dinosauria Scale.svg
Size of several dinosaurs from the Huincul Formation compared to a human

Chakisaurus is known from the Late Cretaceous Huincul Formation of Río Negro Province, Argentina. Many saurischian dinosaurs, including rebbachisaurids ( Cathartesaura , Limaysaurus , and Sidersaura ), [4] [5] titanosaurs ( Argentinosaurus , Bustingorrytitan , Chucarosaurus , and Choconsaurus ), [6] carcharodontosaurids ( Mapusaurus , Meraxes , and Taurovenator ), [7] a megaraptoran ( Aoniraptor ), abelisaurids ( Skorpiovenator , Tralkasaurus , and Ilokelesia ), an elaphrosaurine ( Huinculsaurus ), [8] a paravian ( Overoraptor ), and the unusual avetheropod Gualicho have also been named from the formation. [9] [10] Remains of an unnamed unenlagiid have also been reported. [11] The non-dinosaurian fauna includes fossil fish, sphenodonts, indeterminate squamates, chelid turtles, and eusuchian crocodilians. [1]

Chakisaurus is the first ornithischian from the formation to receive a scientific name; the ungual of an indeterminate ornithopod was the only ornithischian bone previously recovered here. [1]

Related Research Articles

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

Bonitasaura is a genus of titanosaurian dinosaur hailing from uppermost layers of the Late Cretaceous (Santonian) Bajo de la Carpa Formation, Neuquén Group of the eastern Neuquén Basin, located in Río Negro Province, Northwestern Patagonia, Argentina. The remains, consisting of a partial sub-adult skeleton jumbled in a small area of fluvial sandstone, including a lower jaw with teeth, a partial vertebrae series, and limb bones, were described by Sebastian Apesteguía in 2004.

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

Notohypsilophodon is a genus of ornithopod dinosaur from the Late Cretaceous of Argentina. It was described as the only "hypsilophodont" known from South America, although this assessment is not universally supported, and Gasparinisaura is now believed to have been a basal euornithopod as well.

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

Talenkauen is a genus of basal iguanodont dinosaur from the Campanian or Maastrichtian age of the Late Cretaceous Cerro Fortaleza Formation, formerly known as the Pari Aike Formation of Patagonian Lake Viedma, in the Austral Basin of Santa Cruz, Argentina. It is based on MPM-10001A, a partial articulated skeleton missing the rear part of the skull, the tail, and the hands. The type and only species is Talenkauen santacrucensis.

<i>Rocasaurus</i> Genus of titanosaurian sauropod from the Late Cretaceous period

Rocasaurus is a genus of titanosaurian sauropod that lived in South America. Rocasaurus was discovered in Argentina in 2000, within the Allen Formation which is dated to be middle Campanian to early Maastrichtian in age. This genus grew up to 8 metres (26 ft) long, making it one of the smaller sauropods. It seems to be closely related to saltasaurid dinosaurs, like Saltasaurus and Neuquensaurus.

The Huincul Formation is a geologic formation of Late Cretaceous age of the Neuquén Basin that outcrops in the Mendoza, Río Negro and Neuquén Provinces of northern Patagonia, Argentina. It is the second formation in the Río Limay Subgroup, the oldest subgroup within the Neuquén Group. Formerly that subgroup was treated as a formation, and the Huincul Formation was known as the Huincul Member.

<span class="mw-page-title-main">Chorrillo Formation</span> Geologic formation in southern Patagonia, Argentina

The Chorrillo Formation, also named as Chorillo Formation, is a Maastrichtian geologic formation in southern Patagonia, Argentina. The formation is more than 50 metres (160 ft) thick and underlies the Calafate Formation and rests on top of the La Irene Formation.

<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.

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

Elasmaria is a clade of ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia that contains many bipedal ornithopods that were previously considered "hypsilophodonts".

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

Trinisaura is a genus of ornithopod dinosaur that lived during the late Campanian stage of the Upper Cretaceous, around 73 to 72 million years ago in what is now James Ross Island off the coast of northern Antarctica near Patagonia. It is known from a single, incomplete postcranial skeleton that includes several vertebrae, a partial pelvis, and nearly complete right hindlimb. The fossils were collected in 2008 by paleontologists Juan Moly and Rodolfo Coria from the sandstone of the Snow Hill Island Formation. It remained undescribed in the collections of the Museo de La Plata until its description by Coria and colleagues in 2013, being the basis of the novel genus and species Trinisaura santamartaensis. The genus name is to commemorate the efforts of Argentine geologist Trinidad "Trini" Diaz and the Latin root -sauros, meaning "lizard". The species name is after Santa Marta Cove, where the fossils were collected.

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

Morrosaurus is an extinct genus of herbivorous elasmarian dinosaur that lived in the late Cretaceous in Antarctica. The only known species is the type Morrosaurus antarcticus.

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>Overoraptor</i> Extinct genus of theropod dinosaurs

Overoraptor is an extinct genus of paravian theropod of uncertain affinities from the Late Cretaceous Huincul Formation of Argentinian Patagonia. The genus contains a single species, O. chimentoi, known from several bones of the hands, feet, and hips alongside some vertebrae.

<i>Niebla antiqua</i> Extinct species of dinosaur

Niebla is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Period (Campanian-Maastrichtian) of Río Negro province, Argentina. The genus contains a single species, Niebla antiqua, and is known from a partial, non-articulated skeleton. The holotype, found in the Allen Formation, represents an adult individual about nine years old in minimum age.

<i>Maip</i> Genus of megaraptoran dinosaurs

Maip is a genus of large megaraptorid theropod dinosaur from the Late Cretaceous (Maastrichtian) Chorrillo Formation of Santa Cruz, Argentina. The genus contains a single species, M. macrothorax, known from an incomplete, disarticulated skeleton. Maip may represent the largest megaraptorid known from South America, and possibly the world.

<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.

<i>Patagopelta</i> Genus of nodosaurid dinosaurs

Patagopelta is an extinct genus of ankylosaurian dinosaur from the Late Cretaceous Allen Formation of Argentina. The genus contains a single species, P. cristata, known from a partial skeleton. While originally described as a nodosaurine, later discoveries provided support for parankylosaurian affinities for the taxon. Patagopelta is a very small ankylosaur, comparable in size to the dwarf nodosaurid Struthiosaurus, about 2 m (6.6 ft) long.

<i>Yatenavis</i> Extinct genus of birds

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<i>Chucarosaurus</i> Genus of titanosaurian dinosaurs

Chucarosaurus is an extinct genus of titanosaurian dinosaur from the Late Cretaceous Huincul Formation of Argentina. The genus contains a single species, C. diripienda, known from various limb and pelvic bones.

Sidersaura is an extinct genus of rebbachisaurid sauropod dinosaur from the Late Cretaceous Huincul Formation of Argentina. The genus contains a single species, S. marae, known from the remains of four individuals. Sidersaura represents one of the largest known rebbachisaurids.

References

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  2. Vidal, Luciano da Silva; Pereira, Paulo Victor Luiz Gomes da Costa; Tavares, Sandra; Brusatte, Stephen L.; Bergqvist, Lílian Paglarelli; Candeiro, Carlos Roberto dos Anjos (2021-09-02). "Investigating the enigmatic Aeolosaurini clade: the caudal biomechanics of Aeolosaurus maximus (Aeolosaurini/Sauropoda) using the neutral pose method and the first case of protonic tail condition in Sauropoda". Historical Biology . 33 (9): 1836–1856. Bibcode:2021HBio...33.1836V. doi:10.1080/08912963.2020.1745791. ISSN   0891-2963.
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