john harshman

You are making this way more complicated than it needs to be. Feathers
evolved fairly close to the base of Maniraptora, or maybe a bit before.
Flight probably evolved once, but it's unclear exactly where, or which
theropods exactly are secondarily flightless. But let's not confuse
flight with the clade that composes living birds. They could be the only
surviving group of many flying and secondarily flithtless theropods. All
modern birds have a single common, flying ancestor. There is some
ambiguity about exact relationships among Maniraptora, but it's not
nearly as great as you think.

Modern birds are not descended from therizinosaurs, but from something
in the neighborhood of dromaeosaurs or deinonychosaurs. The major
ambiguity is just where troodonts fit.

Read some of these:

Prum, R. O. 2003. Dinosaurs take to the air. Nature 421:323-324.

Pisani, D., A. M. Yates, M. C. Langer, and M. J. Benton. 2002. A
genus-level supertree of the Dinosauria. Proc. R. Soc. Lond. B 269:915-921.

and various papers in Gauthier, J., and L. F. Gall (eds.). 2001. New
perspectives on the origin and early evolution of birds: Proceedings of
the international symposium in honor of John H. Ostrom. Yale University
Press, New Haven.

george

I think some genetic analysis of aves thrown at the issue is in order.

john harshman

Why? It would seem to be irrelevant, unless you can get some genes out
of a variety of extinct theropods.

albaradru

So......


Does anybody know what's goin on enough to explain some of this stuff
to me, I will look up the references, but there is only so much I can
understand as there is much ambiguity and apparent subtelty involved in
the matter...

Thanks

john harshman

You might also want to look at the May 2005 issue of Natural History.
Nice popular article, with tree.

michaelmeapayne

OK. let me see if i can explain this OK since I'm in a hurray.
No.1: Microraptor is a dromeosaur from the early cretaceous of china.
There is no doubt on that. The amazing thing is that its has downy
feathers. However it is also a Juvenal.
No.2: As for Therizinosaurs there still is a lot of debate. there are
presently two main theory's on there classification. One is that they
are a sister group to oviraptorids. However the more widely excepted
idea, proposed by sereno and currie is that they are closely related to
ornothimimids. meaning they were not as closely related to birds.
though more closely than say allosaurus or dilophosaurus.
No.3: Birds are most closely related to ceolosaurs. of which at present
there are five main branches. Dromeosaurs, tyrannosaurs, Oviraptorids,
ornithomimids, and Therizinosaurids. The most closely related to birds
are the dromeosaurs followed by the oviraptorids and tyrannosaurs.
No.4: Maniraptorids are what paleontologists call a clad. they are
animals that have similar characteristics. Though may be of different
families,genera, etc. The main two things that make maniraptorids or at
least what they were thought to be was the fracula or wishbone and the
wrist bone. for a long time just included oviraptorids and dromeosaurs
and of course birds. however new evidence has come to light some of
which has yet to be published. close study of tyrannosaurs shows that
there wrist bone and fraculas are very closely related to that of birds
than to other dinosaurs so this has upset the status quo. So
maniraptors are really just a group that have things similer to birds
but does in no way mean there ancestors.
No.5: And last but not least there evolutionary relationships. By no
means are dromeosaurs and ovirators necessarily the direct ancesters of
birds. especially since most of them come after the first bird
appeared. they are animals with a common ancestor. As a good example is
human evolution. neanderthals and modern humans have a common ancestor
though the neanderthals are in no way our ancestor. the same thing
here. Birds and dromeosaurs had a common ancestor and birds evolved one
way and dromeosaurs the other. though because of the wonderful finds
like microraptor we know they had a common ancestory and can guess what
early bird ancestors were like.

I hope this helps. If you need more help on this let me know.

john harshman

That may be true of the first specimen, the one that was part of
"Archaeraptor". However, the two specimens of Microraptor gui are
adults, and the cool thing about them is that they have four wings with
well developed flight feathers.


I think we can do better than that. They are coelurosaurs, but they are
also maniraptorans, which narrows the field.

That's "clade", meaning that they include a common ancestor and *all*
its descendants. Clades don't actually need to have similar
characteristics. Archosauria, for example, is a clade that includes
species as dissimilar as alligators and albatrosses.

That's "furcula". But that's not a character of Maniraptora. It's found
in many other theropods, for example Allosaurus. The wrist bone in
question is better; it's called a semilunate carpal, and is a crucial character of Maniraptora.


No, but it does mean they are closely related by common descent from an
ancestor possessing that trait.


In fact, as defined, they are clearly not.

michaelmeapayne

ok I will agree on a few thigs that you said though most of what I put
down was rehash from currie when I talked to him last month. clade can
also mean a veriety of things also not just a common ancestor. In fact
the furcula has a lot to do with relationships the shape and fit has a
lot to do with it. Though the semilunate carpal has a lot to do with
it. And i do owe a bit of thanks for johns correction on the furcula. I
never was good in anatomy. My masters thesis is evolutionary
relationships. So i guess i better get that down.

john harshman

That's not true. "Clade" has one meaning only and I would be very
surprised if you could find it used in any other way. There are several
definitions but all are equivalent. A clade is not a common ancestor;
it's a common ancestor and all its descendants.


If you mean that there are characters involving the shape of the furcula
that diagnose Maniraptora, that might well be true. But mere possession
of a furcula, as you seemed to be saying, is not such a character.

michaelmeapayne

yes the mere possession of a furcula does not a all mean a dinosaur is
a maniraptor. The characteristics in the shape do help the diagnosis.
The big gun though is the semilunate carpal. And as for the clade thing
I guess I have to put this the right way A "clade" is a group of
animals that have many things in common thus they would all have a
common ancester. maniraptor really include most ceolosuars. though i
think they all are minus one or two correct me if i'm wrong. however i
used to think of the term Clade as you defined obove for years until
james farlow used the term clade recently in his presentation at the
tyrannosaur symposium. He used the term clade when he was comparing
similarities in footprints. though many of the animals had nothing in
common otherwise. Though I'm not totally agree with what he said i did
find it interesting. His paper on this subject will be published next
year in december.