The most famous of all dinosaurs, the Tyrannosaurus Rex, although being a powerful dangerous predator, is often made fun of for having particularly small arms. Of course, if you were to compare these arms with a human, you would find them to actually be quite large structures reaching about a metre in length, but when compared to the rest of the creature that they are attached to, they look tiny.
But there were some other types of dinosaurs that had even smaller arms than a t-rex and ones that looked far more ridiculous than a tyrant lizard. So why did some dinosaurs have such small arms? Well, in the case of t-rex, it was assumed for a long time that his arms must have been a vestigial trait.
A vestigial trait is a particular part of an animal’s, anatomy the originally evolved in an ancestor to perform a certain function, but over time it has become less important. However, because the trait does not obstruct any other functions of the creatures anatomy.
It may stay around for a while but be reduced in size or might eventually disappear altogether in the animals descendants. So this is what many people thought about. T Rex’s arms, since they were so small compared to the rest of the dinosaur.
This is an understandable conclusion and seemed reasonable. However, the bones of the arm actually show signs of having had large muscles attached to them in life, which would suggest that they were in fact being used for something.
There are lots of ideas for what their purpose was, including, aiding and lifting the animal up off the ground from a lying-down position or possibly in grabbing on to a partner during the mating process.
Another good theory, which is supported by lots of biomechanical evidence, is that the arms were used for holding onto prey while the t-rex delivered a powerful bite. Signs that this might be true include the fact that the bones of the arms were very thick, as well as the presence of powerful muscles in life.
The joints between shoulder and elbow also allowed a very small range of movement, which would have been a useful adaptation for holding on to a struggling animal. So the reason that T Rex’s, arms were that small is likely because the animal was relying much more on use of its mouth to take down prey.
But the arms were not useless and were in fact the perfect size to aid in the delivery of a fatal bite to an unfortunate animal. As I mentioned earlier, there are also a lot of other very small arms dinosaurs, most notably a group of carnivores called Thea belly sauce.
These dinosaurs were very weird-looking animals with much smaller arms than a t-rex. The group contains another fairly well known dinosaur that you may have heard of Carnotaurus. Unlike with tyrannosaurs, however, a belly saw four limbs were almost certainly vestigial traits and would not have had any function in the dinosaurs lifestyle.
The Abella saw arms did not have any wrist bones; instead, the bones that make up the palm of our hands called metacarpals attached straight onto the upper arm bone in these dinosaurs as well as this most members of the group did not even possess claws on their Fingers showing how truly useless these arms would have been for hunting, so why did the Abela sauce have small vestigial arms? There is an interesting idea that, early on in the evolution of the group, a genetic defect occurred in two genes that are related to fallen development, and this led to small stumpy arms becoming inherited by the whole group.
This would explain why they had the arms they did and they must have been able to live in a way that did not require the use of those front limbs, but there was still yet another dinosaur with small reduced four limbs.
This is the very recently named guru Litro. What makes go Litro, particularly strange and unique, is that it was very distantly related to tyrannosaurs, but it also had small two fingered hands. This is an excellent example of convergent evolution in which two or more unrelated animals evolved.
The same structure independently of one another because they were performing the same behaviors. So it would seem that GU alito, which was an ALICE or not a Tyrannosaur, was doing the same thing as t-rex by relying mostly on its massive, powerful head and jaws to do the work of killing prey.
This meant that the four limbs were able to be reduced in relative size over time, but did not disappear entirely or become useless. Stubby structures like in a belly saws because they still had a function in the animals behavior.
All of these weird-looking bits for Natalie are such great examples of the effects that evolution has on every living thing. I find it incredible that were able to learn so much about how an animal that has been dead for millions of years lived and functioned and behaved just from a few fossilized bones, and it’s, amazing that we can track the complicated and confusing History of evolution through these discoveries, if you would like to learn more about our unique and special planets and their life that once lived here and the life you still share it with.