Big reptiles, terrible lizards and bird-like monsters, these are some of the popular names that are usually called for dinosaurs. There are many people who believe that these extinct animals were really a part of the animal world and are also known to come in different sizes and shapes.
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It is believed that dinosaurs were ancestors of bird species as suggested by Thomas Henry Huxley in 1868. But this suggestion was abandoned in the early 20th century when the work of Gerhard Heilmann was released. This work was about the theory or idea that dinosaurs were really descendants of thecondonts and not of birds. It was due of the main evidence that dinosaurs lack the clavicles. However, the later discoveries have showed that dinosaurs did have the clavicles yet these were misidentified as interclavicles as found in Oviraptor.
In the 70’s, the theory for dinosaur-bird was revived by John Ostrom and has gained the momentum with the following decades. This has also included the increase in discoveries of early birds and small theropods. A notable instance where this theory was proven is with the fossils found in the Yixian Formation. With these fossils, experts found various early birds and theropods wherein most have certain types of feathers.
Birds are sharing more than a hundred specific anatomical features with that of theropod dinosaurs. These anatomical features are now basically accepted as the proofs showing that these animals are ancient relatives. Of the various classes of dinosaurs, maniraptoran coelurosaurs are said to be the closest allies of the theropod dinosaurs.
Though there were already proofs showing that birds and dinosaurs are really related, there are a minority of scientists that contrasts these theories. Some of the most notable scientists belonging in this minority are Larry Martin and Alan Feduccia. The said scientists were the ones who proposed that dinosaurs have undergone other evolutionary paths. These paths include the revised versions of the basal archosaur proposal made by Heilmann. Another revised version of this evolutionary path is that the maniraptoran theropods were ancestors of bird species but these theropods are not actually dinosaurs, they were only convergent with the dinosaurs.
Origins of Dinosaurs According to Taxonomy
In 1842, the term Dinosauria was named formally by the paleontologist Sir Richard Owen. He has used the term for referring the sub-order Saurian Reptiles that are now being recognized not only in England but also around the globe. Though this taxonomic name was usually interpreted as reference for the different fearsome characteristics of the dinosaur, Owen used it for the intention of evoking its majesty and size.
With the phylogenetic taxonomy, these creatures are defined as a group that consists of the Neornithes, Triceratops, the MRCA or most recent common ancestor and all other descendants. It was also suggested that the name Dinosauria be completely defined with the respect to the most recent common ancestor of the Iguanodon and Megalosaurus. The reason behind this is that these are 2 of out of the 3 genera that are cited by Richard Owen recognized in the Dinosauria.
In support of the early theories saying that the birds are directly connected with the birds, birds are currently recognized as the sole surviving lineage of the theropod dinosaurs. With the traditional taxonomy, bird species are now considered as a separate class that has already evolved from the early specie of dinosaurs, which are considered as superorder. However, majority of the contemporary paleontologists who were concerned of dinosaurs were rejecting the traditional style of animal classification as they are in favor of the phylogenetic nomenclature.
With the Phylogenetic Nomenclature approach, it is required that a group will only be considered as natural if all the descendants were all considered as members of the group. Since birds are considered as dinosaurs, it was concluded that dinosaurs are not really extinct. This is due to the fact that birds are under the classification of the subgroup Maniraptora, which are also known as coelurosaurs. Coelurosaurs are known as theropods, which are known as saurischians that are dinosaurs.
Other Information about the Origins of Dinosaurs
Archaeopteryx is known as the first bird that has existed. It is cited as one of the famous examples that dinosaurs were really from the bird species. But in the early studies, it is believed that the adaptation of these animals for flight were the reasons why they were able to fly without the use of feathers.
The reason why the Archaeopteryx is considered as a bird is the fact that it has features that are seen in today’s birds. This specie has feathers that are fully-formed, perching feet and also a wish bone. Some evolutionists are also saying that this specie also have claws on the wings and a tail. With these features said, many can say that birds are seen to have these features.
Certain Features Modern Birds and Other Species in the Dinosaur Groups Share
One of the basic features that birds and other species within the dinosaur groups are sharing is the feathers. Physical evidences show that feathers are ancestral trait of dinosaurs though it may have been only present in certain species. There are also non-avian dinosaur groups that were found to have feather-like structures or feathers, proving that they also have the same traits as what modern birds have.
Aside from the feathers, paleontologists also found out that feathered dinosaurs were the missing link between dinosaurs and birds because of their bone structures. With the use of cladistic analysis, the comparison with the skeletons of dinosaurs and birds strengthens the entire case for this missing link.
Along with the skeletons was the soft anatomy that both dinosaurs and birds are also sharing. As said by Patrick O’Connor, the feature that was once found to be only unique with birds was indeed present in its ancestors. This only means that the soft anatomy found in birds were likely found in the structure or anatomy of dinosaurs that easily links the species.
Aside from physical features, there was also behavioral evidence that has strengthened the link of birds with dinosaurs. Some of the behavioral evidences that were suspected to link birds with dinosaurs was the way dinosaurs were sleeping just like how modern birds are sleeping and also the way dinosaurs are brooding in their nest like birds.