The tiny arms of prehistoric carnivores have always baffled scientists. The Tyrannosaurus rex is famously known for its tiny arms disproportionate to its large size. Scientists recently unearthed fossils of a new dinosaur that also had short forearms that give new insights into their purpose.
Scientists hypothesized that the short arms may have been used to grip each other while mating or to help them to stand after falling. Researchers at the Ernesto Bachmann Paleontologicalk Museum in Neuquén, Argentina studied the fossils of the new dinosaur after discovering it in Patagonia.
New Dinosaur Has Similar Arms With T. Rex Despite Being Distantly Related
Researcher Peter Makovicky from the University of Minnesota Twin Cities and his Argentinean colleagues Juan Canale and Sebastian Apesteguía discovered the huge, carnivorous dinosaur called Meraxes gigas in 2012, Science Daily reported.
They have spent several years extracting, preparing, and analyzing the fossils, which provided them clues about the evolution and biology of dinosaurs, particularly the Carcharodontosaurus and Tyrannosaurus rex who both have large bodies and heads but small arms.
The newly discovered dinosaur belonged to the Carcharodontosauridae family, which was a group of large carnivorous dinosaurs that also included Gigantosaurus, one of the latest dinosaurs featured in the Jurassic World: Dominion movie.
M. gigas may not be the largest among its family, but they were still an imposing animal that stood 36 feet tall and weighed approximately 9,000 pounds. Researchers dated the fossils and estimated them to be between 90-95 million years old. The fossils found were almost complete with the skull, hips, and both arms and legs.
Professor Makovicky said they were surprised to find a skeleton similar to a T. rex. The two species are not closely related and are from distant branches of the carnivorous dinosaur family tree. However, their discovery gives them the most complete carcharodontosaurid specimen to study, especially of their paleobiology and true size.
Sexual Selection May Have Caused Smaller Arms in Prehistoric Carnivores
According to the researchers in the study titled, "New Giant Carnivorous Dinosaur Reveals Convergent Evolutionary Trends in Theropod Arm Reduction" published in Current Biology, large, meat-eating dinosaurs in three families of therapods evolved in similar ways. They grew to have large skulls, but smaller arms.
Professor Makovicky explained that the arms reduced in size as a result of the skulls becoming massive. It could be because the skull was being optimized to handle larger prey so the arms had a lesser purpose.
According to Sci-News, the analysis showed that the skull of M. gigas was decorated with crests, furrows, bumps, and small horns. These skull structures appeared late in development when the dinosaur were already adults and was probably used to attract a potential mate.
Professor Makovicky noted that sexual selection is a powerful evolutionary force. However, since it is impossible to directly observe dinosaur behavior, he is not certain about his theory.
More so, carcharodontosaurid dinosaurs evolved very quickly unlike most species that went extinct because they evolve quite slowly. Despite that, M. gigas still went extinct after a few million years of being around. Dr. Canale said that their discovery was one of those finds that answer some questions and opened new ones for future explorations.
RELATED ARTICLE: Why Did T. Rex Have Small Arms? Shorter Forelimbs May Have Saved Them During Feeding Frenzies, Study Claims
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