Archaeopteryx is a genus of early birds, transitional between non-avian dinosaurs and true birds. It was an insectivore in real life, but in Scribblenauts it doesn't eat any insects. It can be rode without being tamed.
Like all birds, Archaeopteryx becomes poultry when killed.
In real life, an Archaeopteryx is no larger than a chicken or a small dog.
The synonyms Elephant Bird and Roc were later differentiated and became separate words, but the synonym Aepyornis (the genus name of the Elephant Bird) didn't get amended.