Meraxes

Meraxes Temporal range: Late Cretaceous, (Cenomanian), ~95–93.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Reconstructed skull
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Carcharodontosauridae
Tribe:	†Giganotosaurini
Genus:	†Meraxes Canale et al., 2022
Species:	†M. gigas
Binomial name
†Meraxes gigas Canale et al., 2022

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]

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]

Meraxes is one of the largest theropods, weighing approximately 4.26 metric tons (4.70 short tons).^[1] Henderson (2023) listed a body length estimate of 9–10 metres (30–33 ft), referencing Canale et al. (2022), but also estimated a body length of 10.2–11.6 metres (33–38 ft) using the pelvic area.^[3] Its skull is 1.27 m (4.2 ft) long, similar to that of Acrocanthosaurus, which has a skull length of 1.23–1.29 m (4.0–4.2 ft).^[1][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.^[1]

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.^[1][2]

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:^[1]

Carcharodontosauridae	Neovenator Concavenator Eocarcharia Lajasvenator Lusovenator Acrocanthosaurus Shaochilong Carcharodontosaurinae Carcharodontosaurus spp. Giganotosaurini Meraxes Tyrannotitan Giganotosaurus Mapusaurus

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]

Carcharodontosauridae

Neovenator Sauroniops Veterupristisaurus Lusovenator Eocarcharia (type skull roof) Concavenator Carcharodontosaurus iguidensis (holotype maxilla) Acrocanthosaurus Eocarcharia (referred maxilla) Meraxes Carcharodontosaurus iguidensis (referred cranial material) Lajasvenator Labocania Shaochilong Carcharodontosaurus saharicus (neotype) Carcharodontosaurus saharicus (described by Stromer in 1931) Tyrannotitan Mapusaurus Giganotosaurus

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 carcharodontosaurids Mapusaurus and Taurovenator.^[6][7] Meraxes was found in an older rock layer than either Mapusaurus and Taurovenator, so it is unlikely they coexisted.^[1][8] The herbivores of the area are represented by the rebbachisaurid sauropods Cathartesaura and Limaysaurus, the titanosaurs Argentinosaurus, Choconsaurus, and Chucarosaurus, and indeterminate iguanodonts.^[9][10][11]