1) Class 2) Subclass archaeornithes 
The Archaeornithes, classically Archæornithes, is an extinct group of the first primitive, reptile-like birds. It is an evolutionary grade of transitional fossils, the primitive birds halfway between dinosaur ancestors and the derived modern birds. Fossils of early birds were poorly known until the late 20th century. Of those known, all fell into...
(from the article `vertebrate`) ...feathers; scales on feet; 4-chambered heart; no teeth; horny beak; lungs with extended air sacs; 12 pairs of cranial nerves; internal ...
[n] - primitive reptile-like fossil birds of the Jurassic or early Cretaceous
subclass Archaeornithes noun primitive reptile-like fossil birds of the Jurassic or early Cretaceous