<u>Answer:</u>
Recent evidence suggest that feathers evolved from scales and suggest that 'feathers and pycnofibers' could be homologous.
<u>Explanation:</u>
- One of the major difficult issue related to bird evolution is the evolution of feathers.
- Feathers are considered as the most 'complex integumentary structures' which are found in vertebrates.
- Evolutionary developmental biology suggests that the 'planar scale structure' is been modified for developing into feathers by 'splitting' to form web like structures.
- Scales and Feathers consist of 'two distinct form of keratin' so it was thought that 'each type was exclusive skin structure' but recent study suggests that they are developmental expressions of same skin structures.
They have a cell membrane, they contain cytoplasm and can replicate themselves through the manner of mitosis.
Answer:
birds
Explanation:
<em>Archaeopteryx</em> is an iconic fossil bird that lived during the Late Jurassic, approximately 150 million years ago. <em>Archaeopteryx</em> is iconic because it is a transitional fossil between non-avian dinosaurs (reptiles) and birds. The osteology of <em>Archaeopteryx</em> indicates that it was similar to that of nonavian theropod dinosaurs, i.e., dinosaurs characterized by hollow bones and three-toed limbs. Unlike modern birds, <em>Archaeopteryx</em> had a full set of teeth, a long tail, three fingers with claws and hyperextensible second toes commonly known as 'killing claws'.
