Final answer:
Protoavis is not the oldest bird; birds originated from maniraptoran theropod dinosaurs approximately 150 million years ago, with Archaeopteryx being one of the oldest known transitional fossils.
Step-by-step explanation:
The statement that Protoavis is the oldest bird is false. Instead, abundant paleontological evidence supports the notion that birds evolved from therapod dinosaurs, specifically the maniraptoran theropods. This evolutionary process began approximately 150 million years ago during the Jurassic period. The oldest known fossil of a dinosaur-bird is Archaeopteryx, which highlights the transition between non-avian dinosaurs and modern birds.
Further, the characteristics such as a flow-through respiratory system with lungs and air sacs are shared between these early bird precursors like Archaeopteryx and Xiaotingia and modern birds, indicating a long evolutionary heritage. Modern birds, characterized by feathers and flight, are grouped into Paleognathae, Galloanserae, and Neoaves, which have been diversifying since the Cretaceous-Paleogene extinction event that wiped out the non-avian dinosaurs.