Abelisaurid Dinosaur: The Tyrannosaurus Rex is known for its small, spindly arms, but as paleontologists discover more members of its family, the species is facing some competition.
In a showdown with a newly discovered abelisaurid, T. rex might have had the upper hand. Its stocky, weak upper limbs would likely appear almost muscular next to those of Koleken inakayali, a bipedal carnivorous dinosaur whose bones were recently found preserved in Patagonia.
Unique Characteristics
In its official scientific debut, the species is described as a unique abelisaurid that closely resembles the famous Argentine Carnotaurus, or “meat-eating bull”, a fearsome horned beast with rough and bumpy skin, featured in Jurassic World.
Physical Traits and Habitat
K. inakayali has no horns and is slightly smaller, but together with Carnotaurus sastrei they were found in the same rock formation in Patagonia.
K. inakayali had no arm bones, but based on the proportions of the rest of the skeleton, it probably had arms similar in size to those of Carnotaurus.
With immobile elbows and only rudimentary wrists joints, these indomitable limbs would probably have hung against its stocky chest as it ran. Even its four digits were not capable of grasping objects.
Roughly 90 to 66 million years ago , at the late Cretaceous end, abelisaurids were the most abundant dinosaurs on planet Earth. T rex lived in North America and Asia, but its South American relatives produced the world’s best fossil record.
Evolutionary Traits of Abelisaurids
Paleontologists still wonder why abelisaurids like T. rex evolved such useless arms for hunting or why they are so particularly small in South American fossils. While some say that T. rex’s claws could have been used for “vicious slashing” or for holding on during sexual relationships, other experts suggest that these weak and short limbs are the evolutionary “leftovers” of long-disparate ancestors.
Perhaps as skulls swelled, abelisaurids relied more on their jaws than their forelimbs to grab prey. Over time, the group of possible pack hunters might have even evolved shorter arms to avoid being bitten during a family feeding frenzy.
There are likely several explanations given the diversity of abelisaurids found around the world. In 2022, scientists described an abelisaurid fossil discovered in South America that had tiny arms and one of the smallest brains ever recorded among members of its family. The skull-arm compromise hypothesis does not seem to apply in all cases.
Insights from Recent Discoveries
“This finding sheds light on the diversity of abelisaurid theropods in Patagonia right before the mass extinction event,” says National Geographic explorer, Diego Pol, who unearthed the species with an international team from Argentina, the USA, and China.
“Our study also analyzes the evolution of abelisaurids and their relatives through time, and identifies pulses of accelerated rates of skull evolution in the Early Cretaceous. It expands what we know about abelisaurids living in this area during the Cretaceous Period and shows that they were more diverse than previously understood.”
This study was published in Cladistics.
