They constitute an evolutionary grade of animals, a wastebasket taxon for any archosaur other than a crocodilian, a pterosaur, or a dinosaur (any basal archosaur).
This is a wastebasket article combining rights that were too important to remain unmentioned, but too unimportant to warrant a separate article status.
Wastebasket taxa are by definition either paraphyletic or polyphyletic, and are therefore not considered to be valid taxa under strict cladistic rules of taxonomy.
