I was just looking at the phylogeny of Avialae and saw that birds go from having long tails made up of many caudal vertebrae (ex: Archaeopteryx, Jixiangornis, Jeholornis) to ones with very few vertebrae and a fused pygostyle (ex: Confuciusornithids, Chongmingia, the opposite birds, etc). Has anyone figured out what mutations caused this to happen?

  • $\begingroup$ have you tried googling pygostyle genetics, because I got a lot of good hits with just that. I am not saying this to be rude but because questions like this are expected to show some attempt to research an answer yourself before asking for help. It is part of the homework question rule. Hint: something like it has evolved in more than just birds. $\endgroup$
    – John
    Commented Mar 21, 2023 at 0:21


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