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Re: Revising Hou et al, 96 (very very long)
Mickey Mortimer wrote:
>Parsimony and my gut feelings. Hence just "I think", not "I propose" or "I
>have evidence for". Beipiaosaurus' preacetabular peduncle looks like the
>pubis was propubic, or perhaps mesopubic. I don't think it's certain
>to code, but that's how it looks to me.
If it is important in this matter, in my soon-to-be finished skeletal
reconstruction, the pubis in Beipiaosaurus comes out mesopubic. And when I
first started, my first guess was that it was propubic, but since there is a
small fragment of bone (probably a small piece of pubis), attach the
relatively complete shaft of the pubis to this bone, and voilá, we have a
mesopubic Beipiaosaurus! This also correlates with the amount of evidence
known from more advanced genera succeeding Beipiaosaurus, they show a shift
from the more mesopubic position (Alxasaurus (condition not precisely known,
but very probable IMHO), Beipiaosaurus) to an position approximately in the
middle (Nothronychus) to the avian opisthopubic
Segnosaurus and Enigmosaurus.
>Patagonykus has a mesopubic pelvis, and alvarezsaurids are thought by many
to be basal paravians or >even basal maniraptorans. My analyses place
Avimimus as sister to alvarezsaurids, and it has a barely >propubic pelvis.
Add the strongly propubic Bagaraatan to this, and you see why I feel the
first maniraptoran >was not opisthopubic. Maniraptorans with opisthopubic
pelvises either have more propubic >"ancestors"(segnosaurs, alvarezsaurids),
or are in the troodontid + deinonychosaur + avialan clade, which I >think
has a high probability of being opisthopubic ancestrally.
This is something I can be happy about! One mesopubic ancestor in the middle
Jurassic (speculation, speculation, speculation...) could have given rise to
the two "clans" of Maniraptors: a propubic one (Bagaraatan and in the
Segnosaurs and Alvarezsaurids this was reversed) and an opisthopubic one
(Deinonychosaurs, avialans). Wonder how this animal would look like, maybe
something for a list discussion: create your own basal Maniraptoran!
>So when people say that because Sinornithosaurus was so birdlike and a
>deinonychosaur, deinonychosaurs were obviously evolving away from the
>Archaeopteryx-like condition, I want to ask them "but what if
>Sinornithosaurus is actually closer to birds than deinonychosaurs?".
It may be possible, since, like you have said, eumaniraptoran phylogeny is
quite uncertain at this time, anything can happen. Your question is probably
based on good evidence to support it, but in my opinion, Sinornithosaurus
could be to basal to be properly placed in any of the groups. It has
similarties to Archaeoperyx that must be taken into account (which is in
your opinion close to birds, as well as the raptor, but more closely to the
former than to the latter) such as the very long fore limbs, but also many
similarities to the Deinonychosaurs, such as the tail. The dice could roll
either way, for now, I'm sticking to Xu et al's 1999 and their diagnosis
untill something better comes along with the needed evidence to support
either of the theories or hypothesis.
>Fam had no justification for his statement either, I was just replying with
>my opinion. Again, it's based on parsimony. Basal oviraptorosaurs and
>Protarchaeopteryx have non-semilunate carpals, but oviraptorids have a
>semilunate shape. What could upset things is Beipiaosaurus, which is said
>to have a semilunate identical to Deinonychus, and thus truly semilunate.
First of all, my name is not Fam, this is because I use my families adress
and that one has fam in front of it because of that. So my name is Rutger :)
After clearifying that, let's move on with this thread.
Like I've said, maybe this has something to do with the unknown basal
Maniraptor which I mentioned earlier this post. That this animal lacked the
semi-lunate carpal, but when the two clans diverged, they each evolved on of
their own, which are all based on the same type of construction. This does
not prelude a relationship between the Segnosaurs and Oviraptorids. Maybe
something like this happened after their split from the basal Maniraptor:
| `- Oviraptorids ---> basal Oviraptorid (non semilunate) ---> advanced
`- Segnosaurs ---> basal Segnosaur (semi-lunate) ---> advanced Segnosaur
Hope this comes out right.... So it would not upset things, if this is
possible of course. This would mean that the semi-lunate carpal is not
homologous, it evolved three times convergently, not likely, but Mother
Nature works in mysterious ways. :)