Birds from theropod dinosaurs...basic concept question.

Question

If this is the suggestion, who amongst you anatomists out there can answer this? If Dinosauria is divided into the groups Saurischia ("lizard-hipped") and Ornithischia ("bird-hipped"), what was the original connection idea between modern birds and theropod dinosaurs since theropods belonged to the "lizard-hipped" group? Do modern birds share a pelvic connection to the Saurischian group more so than the group named for them? I'm super weak on anatomy...

Answer 1

<<If Dinosauria is divided into the groups Saurischia ("lizard-hipped") and Ornithischia ("bird-hipped")...>>

The division is a bit simplistic. Presumably, ornithischians are descendants of saurichians and therefore, by descent, also logically saurichians as well. Ornithischian hips are kind of more bird-like than most saurischians in one feature; namely the angle of a bone called the pubis. It points backwards. However, some saurischians have an "ornithischian-like" angled pubis too, for example birds do. Some non-bird saurischians do as well. A change in the angulation of the pubis is, in evolutionary terms, no big deal.

<<Do modern birds share a pelvic connection to the Saurischian group more so than the group named for them?>>

Yes, it's common descent. Suites of characters are more informative than single characters, as the latter can simply be similarities thrown up by convergence.

Answer 2

I believe that the maniraporids are classified as Saurischia due to ancestry. If you look at the pelvis of Velociraptor or Archaeopteryx, the pubis points backwards like in Ornithischia and this is simply an example of convergent evolution.

Velociraptor skeleton;

http://www.healthstones.com/dinosaurstor...

Other anatomical features that connect Maniraptorian theropods and birds are "hallow" bones, feathers, and several skeletal structural similarities throughout the body.