Birds There are more than 9,020 known species of birds existing in the world, and there are more than 2,250 species in my country. According to the morphological and structural characteristics of birds, they can be divided into 2 subclasses: Archaeornithiae and Modernornithes. The species of Archaeornithes have long been extinct, and there are only fossil specimens called Archaeopteryx lithographica, which is an intermediate type that evolved from reptiles to birds. Neornithes, also known as Neornithes, can be divided into 4 general orders: Dentognathae, Ratites, Penguinoides and Cytothorans. ) and reptiles are more complete than amphibians in terms of morphological structure and physiological characteristics. Therefore, they flourished in the Mesozoic Era. Not only were there many species, but they also had different body shapes and lifestyles, occupying every corner of the land. Therefore, this geological era is also called For the Age of Reptiles. The existing species are only a few remnants of those days.
