Argentinian ‘gargoyle’ shows how huge predatory dinosaurs evolved

Fossils found in Argentina of a ferocious dinosaur with an enormous head covered in gargoyle-like bumps and ridges provide insight into the evolution of some of Earth’s greatest predatory dinosaurs, including a curious trend toward stunted arms .

Scientists said on Thursday they had discovered extensive skeletal remains of a previously unknown species called Meraxes gigas in northern Patagonia, including one of the most complete skulls of a large carnivorous dinosaur ever unearthed. Meraxes, who lived about 90 million years ago during the Cretaceous period, was about 36 to 39 feet (11 to 12 meters) long and weighed about 9,000 pounds (4 metric tons). All meat-eating dinosaurs belonged to a bipedal assembly called theropods. Meraxes was a member of a line of theropods called carcharodontosaurs – the so-called shark-toothed dinosaurs – which included the even larger Giganotosaurus, also from Patagonia, and Carcharodontosaurus, from Africa.

The Meraxes skull was more than 127cm long, according to paleontologist Juan Ignacio Canale from the Argentinian research agency CONICET at the Paleontological Museum Ernesto Bachmann, lead author of the study published in the journal Current Biology https://www. cell.com/current-biology/fulltext/S0960-9822(22)00860-0. “Many of the roof bones of the face and skull were covered with bumps, ridges and furrows, giving it a gnarled appearance like a medieval gargoyle,” said the University of Minnesota paleontologist and co-author of the study, Pete Makovicky.

Meraxes, named after a dragon from the fictional series “Song of Ice and Fire” that inspired the TV show “Game of Thrones”, had strong jaws studded with six-inch (15 cm) serrated teeth and the largest foot claws of all large theropods. “A terrifying sight,” said paleontologist and study co-author Sebastián Apesteguía of CONICET and the Felix de Azara Foundation.

Despite his tall stature, his arms were just over 60cm long – “absurdly short”, Makovicky said. Two other lineages of Cretaceous theropods—tyrannosaurs, which included T. rex from North America, and abelisaurs, which included Carnotaurus from South America—also developed stocky arms.

Due to the incompleteness of the remains of other large carcharodontosaurs, Meraxes offered the first evidence of forelimb reduction in this group. Abelisaurs had four-fingered hands, while carcharodontosaurs reduced this to three and tyrannosaurs to two. Scientists have wondered why three of the largest theropod groups independently evolved short arms that were of little use for predation. All three showed a trend of increasing head size and decreasing forelimb size, suggesting a strong reliance on the skull to bring down prey, the researchers said.

Although short in stature, Meraxes’ arms were sturdy and muscular. “Despite their powerful appearance, it’s hard to imagine they were used much because they barely extend beyond the body and couldn’t have reached the huge mouth,” Makovicky said.

“I’m inclined to think they were used in other kinds of activities, like holding the female during mating or helping to elevate the body from a prone position,” Canale added. Some other lineages of large theropods did not join the trend. The huge Spinosaurus, with an elongated skull well suited to hunting aquatic prey, had arms of intermediate length. Strange Therizinosaurus and Deinocheirus, whose diet differed from other theropods, boasted relatively long arms with huge claws.

Carcharodontosaurs reached their peak of diversity around 90 million years ago, then suddenly disappeared. Meraxes is not the largest of this lineage but its remains are the most complete of the largest carcharodontosaurs, with almost the entire skull, hips and limbs – filling in some gaps in the understanding of this group.

For example, based on the dimensions of the skull of Meraxes, the researchers recalculated the length of the skull of Giganotosaurus at a whopping 5-1/2 feet (168 cm). Giganotosaurus, the largest of this line, was slightly longer but not as heavily built as Tyrannosaurus rex, which lived tens of millions of years later. Dinosaurs of this lineage, Apesteguía said, “are mysterious beasts to us.”

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