Birds and reptiles are both made of eukaryotic cells. Both are heterotrophs, which means that they cannot produce their own food and must eat to survive. Both are chordates (also known as invertebrates, meaning that they contain an endoskeleton and vertebrae). Reptiles and birds both lay external eggs during reproduction of offspring.
Differences are as follows:
- Birds are covered in feathers, whereas reptiles are covered in scales. Interestingly, it is thought that birds evolved from reptiles (think of the pterodactyls) and that feathers are actually specialized scales.
- Birds are warm-blooded (meaning they maintain an internal body heat) whereas reptiles are cold-blooded (take on the temperature of their surroundings).
- Reptiles have teeth whereas birds have beaks.
- Birds have wings and reptiles do not.
- Birds, like mammals, have a four-chambered heart (consisting of two ventricles and two atria). However, reptiles have a three-chambered heart.
I hope this helps!