Thursday, June 27, 2013

Further focus (1)

Let us examine a more detailed hypothesis that:
Long-tailed pterosaurs developed into basal Paraves which later developed into short-tailed Pygostylia .
The teeth of deinonychosaurs were curved and serrated, but not blade-like except in some advanced species such as Dromaeosaurus albertensis. The serrations on the front edge of deinonychosaur teeth were very small and fine, while the back edge had serrations which were very large and hooked.[3] Deinonychosaurs generally had long, winged forelimbs, though these were smaller in some troodontids. The wings usually bore three large, flexible claws.[3]
Pygostylia is a group of birds which includes Confuciusornis and all of the more derived birds; the Ornithothoraces[2]The pygostylians fall into two distinct groups with regard to the pygostyle. The Ornithothoraces have a ploughshare-shaped end, while the more primitive members have a longer, rod-shaped pygostyle.
Avialans diversified into a wide variety of forms during the Cretaceous Period.[25] Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of bird groups, including modern birds (Neornithes). While the earliest forms, such as Archaeopteryx and Jeholornis, retained the long bony tails of their ancestors,[25] the tails of more advanced birds were shortened with the advent of the pygostyle bone in the clade Pygostylia. In the late Cretaceous, around 95 million years ago, the ancestor of all modern birds also evolved better olfactory senses.[26]
Ornithurae (meaning "bird tails" in Greek) is the name of a natural group which includes the common ancestor of IchthyornisHesperornis, and all modern birds as well as all other descendants of that common ancestor.

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