Thread:BastionMonk/@comment-3213993-20150629064705/@comment-3213993-20150910082817

I just took a look at pictures of tail vertebrae of Tyrannosaurus rex and comparing them to tail vertebrae in alligator and birds. The tail vertebrae of the fully grown alligator were very similar to tail vertebrae of adult Tyrannosaurus. Like the alligator, Tyrannosaurus also had a long tail with many vertebrae and no pygostyle, so despite being more closely related to birds than alligators, the activity of HOX genes involved in tail development in Tyrannosaurus was probably more similar to alligator than to birds. As for the neck region, the gene Hoxa-5 has been linked to the possible loss of cervical ribs in birds and mammals (independently). Cervical ribs are present in crocodilians and Tyrannosaurus, so the genetic change or switch that caused the loss of cervical ribs in birds was not yet present in Tyrannosaurus. We need embryo studies to find out the genes responsible though, and that is something that none of us can do. And we would still need to find the genetic changes responsible for these phenotypes.