A newfound species of carnivorous dinosaur experienced disproportionately compact arms, suggesting that this certain anatomical quirk — shared by the mighty but flimsy-armed Tyrannosaurus rex — may have been extra frequent amongst huge predatory dinosaurs than formerly believed.
The recently described species, Meraxes gigas, is named soon after the dragon Meraxes in the fantasy fiction collection “A Music of Ice and Hearth” (the inspiration for HBO’s “Video game of Thrones”) by author George R.R. Martin. Meraxes belonged to a team of theropods — typically bipedal meat-eaters — recognized as Carcharodontosauridae, which includes other dinosaur titans these kinds of as Giganotosaurus, Mapusaurus and Carcharodontosaurus. This group lived throughout the Cretaceous period (about 145 million to 66 million several years ago), but died out prior to the extinction event that killed off all the non-avian dinosaurs and marked the close of the Cretaceous.
Paleontologists excavated the new M. gigas specimen, which was in superb ailment, from the Huincul Development in northern Patagonia, Argentina. The fossils date to the early portion of the Cretaceous, and are imagined to be involving 90 million and 100 million many years previous. Scientists found the bones, which included a in close proximity to-full forelimb, and areas of the cranium, femur and pelvis, in a location that was loaded in fossil product 4 sauropod dinosaurs have been also buried in the same rock layer, reported Juan Canale, a researcher at the Ernesto Bachmann Paleontological Museum in Neuquén, Argentina, and lead creator of a review about the dragon-named theropod.
Canale and his colleagues dug by way of a number of tons of sandstone to achieve the fossil, he advised Dwell Science in an email. The research authors suspect that when the dinosaur died, its continues to be have been swiftly protected by sediments carried by flowing drinking water, which protected the human body from decay.
In daily life, the dinosaur would have weighed nicely above 4.4 tons (4 metric tons), the researchers estimated.
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Even though Meraxes and T. rex the two had wimpy-seeking entrance limbs, they are not close kin in its place, this trait is an illustration of convergent evolution — when distantly associated species evolve similar capabilities, Canale claimed.
The evolution of diminutive arms in these carnivorous cousins suggests that multiple lineages of massive predatory theropods progressed to have lowered forelimbs to fill a particular ecological market.
But not all huge theropods had tiny arms. Some had long forelimbs, these types of as the ornithomimosaur Deinocheirus and the fowl-like theropod Gigantoraptor. This hints that forelimb reduction was not simply just similar to entire body dimensions in theropods. Alternatively, it tracks to some other trait in huge predatory theropod species — very likely cranium size, the research authors reported.
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So, why did some major theropods, like T. rex and Meraxes, have these kinds of little arms? 1 explanation could be that particular predatory capabilities in before species in the Meraxes and T. rex lineages ended up carried out by the arms — but in species that advanced later in the group’s lineage, a substantial head with powerful jaws grew to become a extra effective software for looking prey.
Apparently, preserved structures in Meraxes‘ arm bones advise that its compact arms experienced comparatively large muscle groups. Nevertheless proportionally very small, these limbs may not have been completely ineffective, Canale mentioned.
“I do not consider they had been valuable in predation, presented [that] most of the actions connected to this were most most likely executed by the head. I’m inclined to think that they ended up utilised in other kinds of actions, like keeping the feminine in the course of mating, or assisting to elevate the human body from a prone posture,” Canale advised Live Science.
And Meraxes’ puny arms weren’t the only attribute that caught the paleontologists’ interest. The big dinosaur’s skull was surprisingly ornate, embellished with crests, furrows, bumps and miniature horns. This type of ornamentation commonly seems late in growth, when animals turn into sexually mature, which hints that the elaborate ornamentation performed a role in serving to Meraxes come across a mate.
“Supplied that sexual range is a highly effective evolutionary force, I assume the cranial ornamentations are associated to some sort of show qualities,” Canale mentioned. “But presented that we are unable to straight observe their conduct, it is extremely hard to be sure about this.”
The conclusions were being published July 7 in the journal Current Biology (opens in new tab).
Originally published on Live Science.
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