Birds commun ancestor
There are approximately 10,000 species of birds today. All of these have the same common ancestor: a theropod dinosaur, which means, it walked on two legs and ate meat. Theropods were ancestrally predators, although several groups evolved to become herbivores, omnivores, and piscivores.
The oldest and least evolved bird is the ostrich, followed by other prehistoric birds of the same clade. Evolutionary biologists indicate that the ostrich is a species that has existed for approximately 75 million years.
Primitive and modern birds
All living birds are classified as Neornithes, however there was a significant split at the genetic level about 100 million years ago. Separating the birds into two clades: Palaeognathae (primitive birds) and Neognathae (modern birds).
There are only 6 families of Palaeognathae or primitive birds, characterized by a complex bone structure in the upper jaw. Of these, only one species is capable of flight: the Tinamous of South and Central America.
The other 5 families belong to the same order: THE RATITES. They are primitive non-flying birds and are also characterized by using body language for communication instead of voice, since their vocal cords are very primitive.
Ratite evolution patterns date back to the breakup of Gondwana, the ancient supercontinent that linked Africa, Madagascar, South America, India, Australia and New Zealand, some 80 million years ago.
As for the group of modern birds, the Neognathae, they make up about 10,000 species.
So we can get an idea of how important and valuable ratites are, as Ratites are the closest animals to the extinct dinosaurs.
The skeleton of ratites is different from that of modern birds:
1. Modern birds have a keel on their sternum for the insertion of the pectoral muscles, allowing them to flap their wings with force. In contrast, ratites, and like all extinct dinosaurs, have a flat sternum without a keel. Thus, they do not have the strength to rise into the air, as their pectoral muscles are insignificant.
2. Ratites have separate clavicles, like reptiles. Instead, modern birds have their clavicles fused into a single bone. This allows them the typical movement of the wings when flying. However, ratite wings can move in a very limited way, usually back and forth and not up and down.
3. Ratites wings are very short relative to their body, compared to modern birds. In fact, the ostrich is the bird with the largest number of fingers on its wing (still retaining the original claws of the hand).
4. The feathers are also adapted to the needs of birds. Ratites have primitive feathers whose function is to insulate against heat or cold and are also used for courtship. These feathers are characterized by having separate filaments, thus being useless for flying. In contrast, modern bird feathers have micro hooks to attach the filaments. In this way, they are able to push the air and lift their body up.