famous short arms of Tyrannosaurus Rex This could be the result of a major change in the way giant meat-eating dinosaurs hunted, according to a new study led by researchers at UCL (University College London) and the University of Cambridge.
Research, published in Proceedings of the Royal Society B82 species of theropods, a group of mostly carnivorous, two-legged dinosaurs, were examined. Scientists found that small forelimbs evolved independently in at least five dinosaur lineages, including tyrannosaurids. T. Rex.
Rather than simply being a side effect of growing larger bodies, the study shows that shrinking arms were closely linked to the development of huge, powerful skulls and jaws.
Giant skulls capture prey
The researchers found that dinosaurs with short arms had particularly strong skulls. That relationship was stronger than the relationship between short arms and overall body size.
According to the team, this may reflect a major evolutionary change in hunting strategy. As giant plant-eating dinosaurs like the sauropods became more common, predators may have relied less on catching prey with claws and more on devastating bites.
Lead author Charlie Roger Sherer, a PhD student at UCL Earth Sciences, said: “Everyone knows T. Rex Their arms were short, but other giant theropod dinosaurs also had relatively short forelimbs. carnotaurus He had ridiculously small arms, even smaller T. rex.
“We tried to understand what was driving this change and found a strong correlation between smaller arms and larger, powerfully built heads. The head replaced the arms as a method of attack. It’s a case of ‘use it or lose it’ – the arms are no longer useful and reduce in size over time.
“These adaptations often occur in areas with huge prey. Trying to drag and capture a 100-foot-long sauropod with your claws is not ideal. Attacking and capturing with the jaws may be more effective.”
Sherer said the evidence points to skulls becoming stronger before the arms shrank.
“Although our study identifies correlations and therefore cannot establish cause and effect, it is highly likely that strongly built skulls came before smaller forelimbs. It would not make evolutionary sense for it to be the opposite and for these predators to leave their attack mechanisms without back-up.”
Measuring the strength of dinosaur skulls
To investigate the relationship between arm size and skull strength, researchers developed a new method to measure skull strength. Their approach considered several factors, including the force of the bite, the size of the skull, and how tightly the skull bones were attached. Compact skulls were considered stronger than long, narrow skulls.
Using this system, T. Rex The study ranked it as the strongest skull. was close behind TyrannotitanAnother giant theropod that lived more than 30 million years ago in what is now Argentina T. Rex During the Early Cretaceous period.
The team believes that giant prey animals have triggered an “evolutionary arms race”, in which predators evolved stronger jaws and skulls to overcome fast-moving herbivores. In many cases, these hunters themselves grew to gigantic sizes.
Multiple dinosaur groups developed small weapons
The researchers compared forelimb length with skull length and identified five dinosaur groups with significantly shorter forelimbs. These include tyrannosaurids, abelisaurids, carcharodontosaurids (which include Tyrannotitan), megalosaurids, and ceratosaurids.
Their analysis showed that smaller arms were more strongly associated with skull strength than skull size or total body size.
The study also highlighted that not all of these predators were giants. MajungasaurusFor example, it had a heavy skull and very small arms, yet it weighed only 1.6 tons, about one-fifth of its body weight. T. Rex. The dinosaur lived in Madagascar about 70 million years ago and was still considered an apex predator.
Different paths to the same result
Scientists also found that dinosaur groups shortened their forelimbs in different ways over time.
In abelisaurids, the lower parts of the arms beyond the hand and elbow became dramatically shorter, a trend similar to that in later species. Majungasaurus Develop exceptionally small hands. However, tyrannosaurids showed a more balanced reduction of the entire forelimb.
The researchers concluded that different dinosaur lineages probably reached the same outcome through different evolutionary and developmental pathways.
The study was carried out by a wider research group at UCL focused on the evolution of dinosaurs, working closely with the Natural History Museum. The group includes research fellows, postdoctoral scientists and more than 10 PhD students studying dinosaurs and other vertebrates such as crocodiles and birds.