Meraxes

The holotype of Meraxes, previously called the "Campanas carcharodontosaurid", MMCh-PV 65, was discovered in 2012.[2] Known bones include 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 has the most complete carcharodontosaurid skeleton known from the Southern Hemisphere.[1]

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", is derived from a Greek word meaning "giant", in reference to its large size.[1]

Size compared to a human

Meraxes was a very large theropod, measuring 9–10 metres (30–33 ft) long based on skeletal reconstruction and weighing approximately 4.26 metric tons (4.70 short tons); however, Henderson (2023) suggested that the pelvic area indicates a greater body length range of 10.2–11.6 metres (33–38 ft).[1][3] Its skull alone is 1.27 m (4.2 ft) long, rivaling that of Acrocanthosaurus which has a skull length of 1.23–1.29 m (4.0–4.2 ft). The shapes and proportions of various bones (i.e. skull, scapula, metacarpals, ischial shaft, foot, etc.) indicate that Meraxes and Acrocanthosaurus had similar proportions and body size. It also 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][4]

Life restoration

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 also 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]

Meraxes represents the earliest diverging member of the tribe Giganotosaurini within the Carcharodontosauridae. The cladogram below displays the results of the phylogenetic analysis by Canale et al.[1]

Meraxes gigas reconstruction

Several dinosaurs from the Huincul Formation (Meraxes in dark blue, left)

The fossil remains of Meraxes were recovered from the Huincul Formation. A substantial number of taxa are known to have inhabited this paleoenvironment. The theropods of the area are represented by the paravian Overoraptor, the elaphrosaurine Huinculsaurus, the abelisaurs Skorpiovenator, Tralkasaurus, and Ilokelesia, the fellow giant carcharodontosaurid Mapusaurus, and the megaraptoran Aoniraptor.[5][6] However, Meraxes was found in an older rock layer than Mapusaurus, so they probably did not coexist.[1] The herbivores of the area are represented by the rebbachisaurid sauropods Cathartesaura and Limaysaurus, the titanosaurs Argentinosaurus and Choconsaurus, and indeterminate iguanodonts.[7][8]