Oops...
> 4) number of caudal vertebrae versus loss of teeth in birds, etc. > etc. etc. The list is endless.
I answered the second sentence, but not the first. Here goes:Short tail, no teeth: Neornithes, Confuciusornithidae, *Gobipteryx*, *Archaeorhynchus* yadda yadda. Short tail, teeth all over both jaws: most EK Enantiornithes, *Yanornis* yadda yadda.
Long tail, teeth: *Archaeopteryx* if you want to count it as a bird.Long tail, no or almost no teeth: the *Shenzhouraptor*/*Jeholornis*/*Jixiangornis*/*Dalianraptor* complex; also, *Yandangornis*.
Not correlated.