A newly discovered species of carnivorous dinosaur had disproportionately small arms, suggesting that this particular anatomical feature – shared by the powerful but weakly armed tyrannosaurus rex – may have been more common among large predatory dinosaurs than previously thought.
Newly described species, Meraxes gigas, is named after dragon Meraxes in the fantastic series “or Song of Ice and Fire” (the inspiration for HBO’s “Game of Thrones”) by writer George RR Martin. Meraxes it belonged to a group of theropods—primarily bipedal carnivores—known as the Carcharodontosauridae, which includes other dinosaur titans such as Giganotosaurus, Mapusaurus AND Carcharodontosaurus. This group lived during the Cretaceous period (about 145 million to 66 million years ago), but died out before extinction event that killed off all non-bird dinosaurs and marked the end of the Cretaceous.
Paleontologists excavated the new one M. gigas specimen, which was in excellent condition, from the Huincul Formation in northern Patagonia, Argentina. The fossils date to the early Cretaceous and are thought to be between 90 million and 100 million years old. Scientists found the bones, which included a nearly complete forelimb, and parts of the skull, femur and pelvis, in a site that was rich in fossil material; the four sauropod dinosaurs were also buried in the same rock layer, said Juan Canale, a researcher at the Ernesto Bachmann Paleontological Museum in Neuquén, Argentina, and lead author of a study about the theropod called dragon.
Canale and his colleagues dug through several tons of sandstone to reach the fossil, he told Live Science in an email. The authors of the study suspect that when the dinosaur died, its remains were quickly covered by sediment carried by flowing water, which protects the body from decay.
In life, the dinosaur would have weighed more than 4.4 tons (4 metric tons), scientists estimated.
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although Meraxes AND T. rex both had poor looking forelimbs, they are not related; instead, this trait is an instance of convergent evolution — when distantly related species evolve similar characteristics, Canale said.
The evolution of small arms in these carnivorous cousins suggests that multiple lineages of large predatory theropods evolved to have reduced limbs to fill a specific ecological niche.
But not all large theropods had small wings. Some had long forelimbs, such as ornithomimosaurs Deinocheirus and the bird-like theropod Gigantoraptor. This suggests that forelimb reduction was not simply related to body size in theropods. Instead, it traces back to several other traits in large predatory theropod species — likely skull size, the study authors reported.
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So why some large theropods like T. rex AND Meraxes, do you have such small weapons? One explanation could be that some predatory functions in previous species in Meraxes AND T. rex bloodlines were carried by the wings – but in species that evolved later in the lineage of the group, a large head with powerful jaws became a more effective tool for hunting prey.
It is interesting that the structures preserved in MeraxesThe arm bones suggest that his small arms had relatively large muscles. Although proportionally small, these limbs may not have been completely useless, Canale said.
“I don’t think they were useful in the robbery, considering [that] most of the actions related to this were most likely performed by the head. I’m inclined to think that they were used in other types of activities, such as holding the female during mating, or helping to raise the body from a lying position,” Canale told Live Science.
AND Meraxes’ the skinny arms weren’t the only feature that caught paleontologists’ attention. The skull of the great dinosaur was amazingly ornate, decorated with ridges, grooves, bumps and miniature horns. This type of ornamentation usually appears late in development, when animals become sexually mature, suggesting that elaborate ornamentation played a helpful role. Meraxes find a friend
“Given that sexual selection is a powerful evolutionary pressure, I think skull ornamentation is linked to some display traits,” Canale said. “But given that we can’t directly observe their behavior, it’s impossible to be sure of that.”
The findings were published July 7 in the journal Current Biology (opens in new tab).
Originally published in Live Science.