Chakisaurus
{{Short description|Extinct genus of ornithopod dinosaurs}}
{{Speciesbox
| fossil_range = Late Cretaceous, {{fossilrange|Cenomanian|Turonian|(Cenomanian–Turonian)}}
| image =Chakisaurus LMR.png
| image_caption =Life restoration of an adult Chakisaurus along with two juvenile individuals
| display_parents = 2
| genus = Chakisaurus
| species = nekul
| authority = 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.
Discovery and naming
{{Location map|Argentina
|width = 225px
|coordinates={{coord|39|23|52|S|68|37|4|W|display=inline}}
|caption= Chakisaurus type locality at Pueblo Blanco Natural Reserve, Argentina
|pushpin_relief=1
}}
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 {{convert|500|m|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.{{Cite journal |last1=Alvarez-Nogueira |first1=Rodrigo |last2=Rozadilla |first2=Sebastián |last3=Agnolín |first3=Federico L. |last4=Garcia Marsà |first4=Jordi A. |last5=Motta |first5=Matias J. |last6=Novas |first6=Fernando E. |date=July 2024 |title=A new ornithopod from the Upper Cretaceous (Huincul Formation) of Northwestern Patagonia, Argentina. Implications on elasmarian postcranial anatomy |journal=Cretaceous Research |volume=159 |pages=105874 |doi=10.1016/j.cretres.2024.105874|bibcode=2024CrRes.15905874N }}
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".
Chakisaurus represents the tenth basal ornithopod named from South America. However, it is only the first ornithischian from the Huincul Formation to receive a scientific name.
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.
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.{{Cite journal |last1=Vidal |first1=Luciano da Silva |last2=Pereira |first2=Paulo Victor Luiz Gomes da Costa |last3=Tavares |first3=Sandra |last4=Brusatte |first4=Stephen L. |last5=Bergqvist |first5=Lílian Paglarelli |last6=Candeiro |first6=Carlos Roberto dos Anjos |date=2021-09-02 |title=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 |journal=Historical Biology |language=en |volume=33 |issue=9 |pages=1836–1856 |doi=10.1080/08912963.2020.1745791 |bibcode=2021HBio...33.1836V |issn=0891-2963}}{{Cite journal | url=https://www.sciencedirect.com/science/article/pii/S0195667119302460 | title=Osteology of Ornithopod Macrogryphosaurus gondwanicus (Dinosauria, Ornithischia) from the Upper Cretaceous of Patagonia, Argentina | last1=Rozadilla | first1=Sebastián | last2=Cruzado-Caballero | first2=Penélope | last3=Calvo | first3=Jorge O. | journal=Cretaceous Research | year=2020 | volume=108 | page=104311 | doi=10.1016/j.cretres.2019.104311| bibcode=2020CrRes.10804311R | s2cid=213679041 }}
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:
{{clade
|{{clade
|1=Tenontosaurus spp.
|label2=Iguanodontia
|2={{clade
|1={{clade
|2={{clade
|1=Vegagete ornithopod
|2=Fostoria
|3=Rhabdodontidae }} }}
|label4=Dryomorpha
|4={{clade
|1={{clade
|1={{clade
|1=Dryosaurus
|2={{clade
|1=Valdosaurus
|2=Dysalotosaurus }} }}
|3={{clade
|1=Camptosaurus aphanoecetes {{small|(Uteodon)}}
|2={{clade
|2=Camptosaurus dispar }} }} }}
|3={{clade
|label2=Elasmaria
|2={{clade
|1=Talenkauen
|2={{clade
|1=Chakisaurus
|2=Morrosaurus
|5=Kangnasaurus
|6=Anabisetia
}} }} }} }} }} }} }}
Palaeoenvironment
File:Huincul Formation Dinosauria Scale.svg 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),{{cite journal |last1=Calvo |first1=Jorge O. |last2=Salgado |first2=Leonardo |title=Rebbachisaurus tessonei sp. nov. a new Sauropoda from the Albian-Cenomanian of Argentina; new evidence on the origin of the Diplodocidae |journal=Gaia |volume=11 |date=1995 |pages=13–33 |url=https://www.dinochecker.com/papers/Calvo%2BSalgado-%5B1995%5D-Rebbachisaurus-tessonei.pdf |archive-url=https://web.archive.org/web/20210923134140/http://www.dinochecker.com/papers/Calvo+Salgado-%5B1995%5D-Rebbachisaurus-tessonei.pdf |archive-date=23 September 2021 }}{{Cite journal |last1=Lerzo |first1=Lucas Nicolás |last2=Gallina |first2=Pablo Ariel |last3=Canale |first3=Juan Ignacio |last4=Otero |first4=Alejandro |last5=Carballido |first5=José Luis |last6=Apesteguía |first6=Sebastián |last7=Makovicky |first7=Peter Juraj |date=2024-01-03 |title=The last of the oldies: a basal rebbachisaurid (Sauropoda, Diplodocoidea) from the early Late Cretaceous (Cenomanian–Turonian) of Patagonia, Argentina |journal=Historical Biology |volume=37 |issue=2 |language=en |pages=208–233 |doi=10.1080/08912963.2023.2297914 |issn=0891-2963}} titanosaurs (Argentinosaurus, Bustingorrytitan, Chucarosaurus, and Choconsaurus),{{Cite journal |last1=Simón |first1=M. E. |last2=Salgado |first2=L. |year=2023 |title=A new gigantic titanosaurian sauropod from the early Late Cretaceous of Patagonia (Neuquén Province, Argentina) |journal=Acta Palaeontologica Polonica|doi=10.4202/app.01086.2023 |doi-access=free }} carcharodontosaurids (Mapusaurus, Meraxes, and Taurovenator),{{cite journal |last1=Canale |first1=Juan I. |last2=Apesteguía |first2=Sebastián |last3=Gallina |first3=Pablo A. |last4=Mitchell |first4=Jonathan |last5=Smith |first5=Nathan D. |last6=Cullen |first6=Thomas M. |last7=Shinya |first7=Akiko |last8=Haluza |first8=Alejandro |last9=Gianechini |first9=Federico A. |last10=Makovicky |first10=Peter J. |title=New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction |journal=Current Biology |date=July 2022 |volume=32 |issue=14 |pages=3195–3202.e5 |doi=10.1016/j.cub.2022.05.057 |pmid=35803271 |s2cid=250343124 |doi-access=free |bibcode=2022CBio...32E3195C }} a megaraptoran (Aoniraptor), abelisaurids (Skorpiovenator, Tralkasaurus, and Ilokelesia), an elaphrosaurine (Huinculsaurus),{{cite journal |last1=Baiano |first1=Mattia A. |last2=Coria |first2=Rodolfo A. |last3=Cau |first3=Andrea |title=A new abelisauroid (Dinosauria: Theropoda) from the Huincul Formation (lower Upper Cretaceous, Neuquén Basin) of Patagonia, Argentina |journal=Cretaceous Research |date=June 2020 |volume=110 |pages=104408 |doi=10.1016/j.cretres.2020.104408 |bibcode=2020CrRes.11004408B |s2cid=214118853 }} a paravian (Overoraptor), and the unusual avetheropod Gualicho have also been named from the formation.{{cite journal |last1=Cerroni |first1=M.A. |last2=Motta |first2=M.J. |last3=Agnolín |first3=F.L. |last4=Aranciaga Rolando |first4=A.M. |last5=Brissón Egli |first5=F. |last6=Novas |first6=F.E. |year=2020 |title=A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina |journal=Journal of South American Earth Sciences |volume=98 |page=102445 |doi=10.1016/j.jsames.2019.102445 |bibcode=2020JSAES..9802445C |s2cid=213781725}}{{cite journal |author1=Matías J. Motta |author2=Federico L. Agnolín |author3=Federico Brissón Egli |author4=Fernando E. Novas |year=2020 |title=New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana |journal=The Science of Nature |volume=107 |issue=3 |pages=Article number 24 |bibcode=2020SciNa.107...24M |doi=10.1007/s00114-020-01682-1 |pmid=32468191 |hdl=11336/135530 |s2cid=218913199|hdl-access=free }} Remains of an unnamed unenlagiid have also been reported.{{Cite journal |last1=Agnolin |first1=Federico L. |last2=Gonzalez Riga |first2=Bernardo J. |last3=Aranciaga Rolando |first3=Alexis M. |last4=Rozadilla |first4=Sebastián |last5=Motta |first5=Matías J. |last6=Chimento |first6=Nicolás R. |last7=Novas |first7=Fernando E. |date=2023-02-02 |title=A new giant titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Northwestern Patagonia, Argentina |url=https://www.sciencedirect.com/science/article/pii/S0195667123000150 |journal=Cretaceous Research |volume=146 |language=en |pages=105487 |doi=10.1016/j.cretres.2023.105487 |bibcode=2023CrRes.14605487A |issn=0195-6671|url-access=subscription }} The non-dinosaurian fauna includes fossil fish, sphenodonts, indeterminate squamates, chelid turtles, and eusuchian crocodilians.
References
{{Reflist}}
{{Ornithopoda|O.}}
{{Taxonbar|from=Q124813502}}
Category:Taxa named by Fernando Novas