Dinosaurs that were destroyed or have continuity in today's birds?

1998/03/01 Nuñez-Betelu, Koldo Iturria: Elhuyar aldizkaria

• Paleontologia
• Arkeologia

Who does not know the Velocirapto de Jurassic Park? Although these dinosaurs looked like featherless ostriches and appear in this science-fiction film, they actually lived, and many other dinosaurs of great poultry appearance. Examples of the latter are, among others, those found in the Cretaceous of China and the Iberian Peninsula. But, although these animals looked like birds, we must not forget that they were true dinosaurs and not birds. The hypothesis that the Chinese dinosaur could have feathers was also published, but this hypothesis was not accepted because the tests were scarce. The Iberian peninsula, for its part, was excavated at the site of Las Hoyas de Cuenca, and in addition to the fossil skeleton of the animal, in the lithographic limestones that kept it appeared a unique mold of leather, but without feathers.

The one in Cuenca, which is a complete skeleton plus a leather mould, allowed us to know how some avian dinosaurs were 125 million years ago. Through it we know that these animals, unlike Velocirapto, resembled the pelicans, with sacks under the long beak and a large bargain over the head.

But the birds, what? When did they appear? Actually, the older birds appeared before the aforementioned Chinese or Iberian animal, the Jurassic. The best known of the first birds is the Archaeopteryx lithographica, from 145 million years ago. This fossil bird has often been used as proof of the Theory of Evolution, since the seven fossils known today by this animal, both reptiles and birds, have different characteristics. This shows that Archaeopteryx is a transition being between reptiles and birds. However, if the fossils of this bird did not present the feathers so well preserved, probably the Archaeopteryx would be considered a simple reptile, especially for its characteristics. And the famous Archaeopteryx, probably, could fly in a very clumsy way, with long jumps as much. Therefore, between Archaeopteryx and real birds there was still little similarity.

On the other hand, a toothed bird from the lithographic caleras of La Pedrera in the Montsec mountain range of Lleida was more like birds. The fossil found still belonged to a sparrow bird of nesting age and appeared on rocks 10 million years later than Archaeopteryx, that is, on rocks 135 million years ago. His skull had many characteristics of sauriscous dinosaurs, carnivores. On the contrary, the birds had the characteristics of today's birds, such as the wings, feathers and the light and well-developed bird skeleton.

In another site almost as old as the Lleida site, the aforementioned of Cuenca, dinosaurs in the form of birds and fossils of real birds such as Eoalulavi, Iberomesornis and Concornis were found together. Moreover, although the characteristics of the skeletons of these fossils show that they are real birds, in the limestones that housed a fossil specimen of the Eoalulavi hoyasis also appeared exact copies of the slabs of the bird.

Therefore, the relationship between dinosaurs and birds, or what is the same, the evolution of dinosaurs towards birds, seems demonstrated. In fact, this has been the hypothesis that has been used mostly in the last 25 years among paleontologists, and by this way most research has gone. For example, the fossil of the dinosaur Unenlagia comahuensis, discovered in the Cretaceous Superior of Argentina, would also foster the relationship between dinosaurs and birds. The unenlage has been found in rocks 90 million years ago and, although it is not known the pen, presents a series of features of birds such as the anterior extremities that fold as wings and the transitional pelvis between reptiles and birds.

However, there are paleontologists who still do not accept the hypothesis of the union between dinosaurs and birds. According to them, the origin of birds and dinosaurs is found in two hypothetical branches different from the Arcoaurs, very primitive reptiles that inhabited 250 million years ago. This idea had a great force until the 1970s, to later be discarded.

However, some paleontologists continued to work on this hypothesis and have recently made known the discovery that would drive this hypothesis. Thus, the “fingers” of the wings of the birds would be the same as the directly evolved crocodiles of the arcoaurs, but not those of the dinosaurs.

This could show that birds and dinosaurs followed different evolutionary paths. However, more evidence is still needed to rule out a hypothesis that has remained firm in the last 25 years, the evolutionary relationship between dinosaurs and birds. On the other hand, paleontologists explain that dinosaurs disappeared 65 million years ago, at the end of the Cretaceous, per secula seculorum. But the birds were not destroyed.

But, among other things, if the Chorizo de Lleida is a transformed dinosaur, and this is demonstrated by a series of characteristics that, far from disappearing, have managed to last until today.