Signs of Similarity between Modern Birds and Reptiles
- Unlike amphibians, birds and reptiles have dry skin.
- The feathers of birds, like the scales of reptiles, are composed of horny matter.
- On the legs of birds there is a scaly cover, similar to the scales of reptiles.
- Birds, like reptiles, have a cloaca.
- Eggs laid by birds are rich in yolk, have shells (like crocodiles and turtles, bird eggs are covered with a calcareous shell).
- The similarity of the embryos (gill slits, rudiments of the limbs).
- In modern tropical birds of the goatzin (living in the jungle of the South American Amazon River), chicks have fingers on their wings, with which they cling to tree branches.
The origin of birds
The immediate ancestors of birds have not yet been established. Scientists suggest that birds could have descended from the descendants of ancient reptiles that moved on their hind legs, similar to birds. Their front legs were short and tenacious. Some of these dinosaurs moved to life in trees, could jump from branch to branch. Subsequently, the scales on the forelimbs and tail were transformed into feathers. Such animals could already fly from tree to tree.
In the XIX century. in Germany, two fossilized impressions of the skeletons and feathers of an animal the size of a magpie that lived on Earth about 180 million years ago were found on shale. This animal was called the first bird, or Archeopteryx.
The forelimbs of Archeopteryx bore a strong resemblance to bird wings. The tarsus was developed in the hind limbs, the fingers were located, like in many birds, – three fingers forward, and one back.
However, jaws with teeth, an elongated tail with 20 vertebrae and a fan-shaped arrangement of feathers, bones not filled with air, the absence of a keel on the sternum, the presence of developed fingers on the wings, and other signs indicated that the first birds did not fly well and led an arboreal lifestyle.
Recently, fossil remains of an older pioneer bird, Protoavis, have been found in North America. She lived 225 million years ago and bore more signs of resemblance to modern birds than Archeopteryx.
In protoavis, a keel was developed on the sternum, which indicates its fitness for flight. The jaws had fewer teeth and were more like a beak. Many of the skeletal bones were hollow, like those of birds.
Protoavis is a possible ancestor of modern birds, and Archeopteryx is a special lateral branch in the development of ancient reptiles.
The value of birds in nature and human life
Birds are a food source for animals and humans; down of birds serves as a heater for clothing and household items of a person.
Birds regulate insects and small rodents; participate in the pollination of plants, the spread of fruits and seeds. Birds can spread human infectious diseases – ornithosis.