Meraxes Explained

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.[1]

Discovery and naming

The holotype of Meraxes, MMCh-PV 65, was discovered in 2012. Known from a nearly complete skull, pectoral and pelvic elements, partial forelimbs, complete hindlimbs, fragmentary ribs and cervical and dorsal vertebrae, a sacrum, and several complete caudal vertebrae, it represents the most complete carcharodontosaurid skeleton known from the Southern Hemisphere.[1] The specimen was referred to as the "Campanas carcharodontosaurid" before its description as a new species in 2022.[2]

Meraxes gigas was described in 2022 by Canale et al. based on these remains. The generic name, "Meraxes", honors a dragon ridden by Queen Rhaenys Targaryen in the George R. R. Martin novel series, A Song of Ice and Fire. The specific name, "gigas", means "giant" in Greek, in reference to its large size.[1]

Description

Meraxes is one of the largest theropods, weighing approximately 4.26MT. Henderson (2023) listed a body length estimate of 9m-10mm (30feet-30feetm), referencing Canale et al. (2022), but also estimated a body length of 10.2m-11.6mm (33.5feet-38.1feetm) using the pelvic area.[3] Its skull is long, similar to that of Acrocanthosaurus, which has a skull length of .[4] The shapes and proportions of various bones, including the skull, scapula, metacarpals, ischial shaft, and foot, indicate that Meraxes and Acrocanthosaurus had similar proportions and body size. Meraxes possessed reduced forelimbs, an instance of convergent evolution that occurred independently in four different lineages: Carcharodontosauridae, Abelisauridae, Tyrannosauridae, and Alvarezsauridae. Additionally, the second toes possess an enlarged claw, almost twice as long as the claw on the fourth toe.

Osteohistological analysis of the holotype suggests the individual could have been between 39 and 53 years old when it died, having reached skeletal maturity approximately 4 years prior to its death (between 35 and 49 years old), making it the longest-lived non-avian theropod currently known. Meraxes was determined to have grown to large size by extending its growth period (hypermorphosis), rather than increasing its relative growth rate (acceleration) through development as in Tyrannosaurus, to which it was compared.

Classification

Canale et al. (2022) recovered Meraxes as the earliest diverging member of the tribe Giganotosaurini within the Carcharodontosauridae. The results of their phylogenetic analyses are displayed in the cladogram below:

Cau (2024) also recovered similar relationships for Meraxes, but not in a clade with Tyrannotitan, Giganotosaurus, and Mapusaurus, as suggested by Canale et al. (2022).[5]

Paleoenvironment

The fossil remains of Meraxes were recovered from the Huincul Formation. A substantial number of taxa are known to have inhabited this paleoenvironment. Theropods from the formation include the paravian Overoraptor, the elaphrosaurine Huinculsaurus, the abelisaurs Skorpiovenator, Tralkasaurus, and Ilokelesia, the megaraptoran Aoniraptor, and the fellow giant carcharodontosaurid Mapusaurus.[6] [7] Meraxes was found in an older rock layer than Mapusaurus, so it is unlikely they coexisted. The herbivores of the area are represented by the rebbachisaurid sauropods Cathartesaura and Limaysaurus, the titanosaurs Argentinosaurus, Choconsaurus, and Chucarosaurus, and indeterminate iguanodonts.[8] [9] [10]

Notes and References

  1. Canale . Juan I. . Apesteguía . Sebastián . Gallina . Pablo A. . Mitchell . Jonathan . Smith . Nathan D. . Cullen . Thomas M. . Shinya . Akiko . Haluza . Alejandro . Gianechini . Federico A. . Makovicky . Peter J. . New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction . Current Biology . July 2022 . 32 . 14 . 3195–3202.e5 . 10.1016/j.cub.2022.05.057 . 35803271 . 250343124 . free . 2022CBio...32E3195C .
  2. Cullen. Thomas M.. Canale. Juan I.. Apesteguía. Sebastián. Smith. Nathan D.. Hu. Dongyu. Makovicky. Peter J.. 25 November 2020. Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution. Proceedings of the Royal Society B: Biological Sciences. 287. 1939. 20202258. 10.1098/rspb.2020.2258. 33234083. 7739506. 227154091.
  3. Henderson. Donald M.. 2023. Growth constraints set an upper limit to theropod dinosaur body size. The Science of Nature. 110. 1. 4. 10.1007/s00114-023-01832-1. 2023SciNa.110....4H .
  4. Currie. Philip J.. Carpenter . Kenneth. 2000. A new specimen of Acrocanthosaurus atokensis (Theropoda, Dinosauria) from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA. Geodiversitas. 22. 2. 207–246.
  5. Cau . Andrea . A Unified Framework for Predatory Dinosaur Macroevolution . Bollettino della Società Paleontologica Italiana . 2024 . 63 . 1 . 1-19 . 10.4435/BSPI.2024.08 .
  6. Matías J. Motta . Federico L. Agnolín . Federico Brissón Egli . Fernando E. Novas . 2020 . New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana . The Science of Nature . 107 . 3 . Article number 24 . 2020SciNa.107...24M . 10.1007/s00114-020-01682-1 . 32468191 . 11336/135530 . 218913199. free .
  7. Cerroni . M.A. . Motta . M.J. . Agnolín . F.L. . Aranciaga Rolando . A.M. . Brissón Egli . F. . Novas . F.E. . 2020 . A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina . Journal of South American Earth Sciences . 98 . 102445 . 10.1016/j.jsames.2019.102445 . 2020JSAES..9802445C . 213781725.
  8. Calvo . Jorge O. . Salgado . Leonardo . Rebbachisaurus tessonei sp. nov. a new Sauropoda from the Albian-Cenomanian of Argentina; new evidence on the origin of the Diplodocidae . Gaia . 11 . 1995 . 13–33 . https://web.archive.org/web/20210923134140/http://www.dinochecker.com/papers/Calvo+Salgado-%5B1995%5D-Rebbachisaurus-tessonei.pdf . 23 September 2021 .
  9. Baiano . Mattia A. . Coria . Rodolfo A. . Cau . Andrea . A new abelisauroid (Dinosauria: Theropoda) from the Huincul Formation (lower Upper Cretaceous, Neuquén Basin) of Patagonia, Argentina . Cretaceous Research . June 2020 . 110 . 104408 . 10.1016/j.cretres.2020.104408 . 2020CrRes.11004408B . 214118853 .
  10. Agnolin . Federico L. . Gonzalez Riga . Bernardo J. . Aranciaga Rolando . Alexis M. . Rozadilla . Sebastián . Motta . Matías J. . Chimento . Nicolás R. . Novas . Fernando E. . 2 February 2023 . A new giant titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Northwestern Patagonia, Argentina . Cretaceous Research . 146 . en . 105487 . 10.1016/j.cretres.2023.105487 . 2023CrRes.14605487A . 0195-6671.