Fossils of a monstrous dinosaur found in Argentina with a massive head covered in shards and reminiscent of a gargoyle are providing insight into the evolution of the planet's largest predatory dinosaurs with finned arms. including a curious tendency towards .
Scientists said on July 7 that they discovered the extensive skeletal remains of a previously unknown species of Meraxus gigas in northern Patagonia, including the complete skull of a large meat-eating dinosaur. Meraxus, which lived in the Cretaceous period about 90 million years ago, was about 11 meters to 12 meters long and weighed about 4 tons.
All meat-eating dinosaurs belonged to a bipedal assemblage called theropods. Mirax was a member of a theropod lineage called the Carcharodontosaurus - the so-called shark-toothed dinosaur - which included the much larger Giganotosaurus, also from Patagonia, and the Carcharodontosaurus from Africa.
According to Juan Ignacio Canal, a paleontologist at Argentina's research agency CONICET at the Ernesto Bachmann Paleontological Museum, lead author of the study, published in the journal Current Biology, Meraxus' skull was more than 127 centimeters long.
"Many of the bones in the face and the roof of the skull were covered with bumps, ridges and furrows, giving it the appearance of a medieval gargoyle," said University of Minnesota paleontologist and study author Pat Makowicki.
Meracus, named after a dragon from the "Ice and Fire" fictional series that inspired the TV show "Game of Thrones," had powerful jaws with 15-centimeter serrated teeth. and had the largest foot claws of any large theropod.
"A scary scene," said biologist and study co-author Sebastián Aposteguia of CONICET and the Felix de Azara Foundation.
Despite its large body size, its arms were just over 60 centimeters long — "extremely short," Makowiecki said.
Two other Cretaceous theropod lineages — Tyrannosaurus, which included North America's T. rex, and Abelosaurus, which included South America's Carnotaurus — also developed stubby arms.
Due to the incompleteness of the remains of other large carcharodontosaurs, Meraxus provided the first evidence of predation in this group. Abelisaars had four fingers, while Carcharodontosaurs reduced it to three and Tyrants two.
Scientists have wondered why the three main theropod groups independently developed small weapons of little use in hunting. All three showed a trend toward increased head size and decreased forelimb size, suggesting a greater reliance on the skull to reduce prey, the researchers said.
Despite being diminutive in size, Mirax's arms were strong and muscular.
"Despite their powerful appearance, it is hard to imagine that they were used much because they barely extended beyond the body and could not have reached the large mouth," Makowicki said.
"I'm inclined to think that they were used in other types of activities, such as holding females during mating or helping to lift the body from a vulnerable position," Cannell added.
Some other lineages of large theropods did not participate in this trend. Most Spinosaurus, with a long skull well adapted for hunting aquatic prey, had arms of medium length. The odd therizinosaurus and Denochirus, whose diet differed from that of other theropods, had large claws on relatively long arms.
Carcharodontosaurs reached their peak about 90 million years ago, then suddenly disappeared.
Mirax is not the largest of the genus, but its remains are among the most complete of the largest carcharodontosaurs, with nearly complete parts of the skull, pelvis and limbs - filling some of the gaps in the understanding of the group.
For example, based on the dimensions of the Meraxes skull, the researchers recalculated the Giganotosaurus skull length to 168 cm. Giganotosaurus, the largest of this lineage, was slightly taller but not quite as massive as Tyrannosaurus rex, which lived tens of millions of years later.
Dinosaurs in this lineage, Apesteguia said, "are mysterious animals to us."
