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Allosauria, redefined [was Re: Deinocheirus]



Something I've been preparing for two months or five years, which ever 
way you want to look at it.

I wrote:
>>Metriacanthosauridae ~ *Metriacanthosaurus* + *Yangchuanosaurus*, 
>>their common ancestor, and all descendants thereof, minus sister 
>>group Allosauridae.

>Word to the wise: nevernevernever add more than one inclusive anchor
>taxon (anchor taxon: the taxa you use to define the group, eg. yang, 
>metria and Allosauridae (and by commutation, its anchors _Allosaurus_ 
>and _Acrocanthosaurus_), in this case) in a stem-based definition. >You 
are assuming that the tree topology you currently see will hold >up to 
continued research. If it does not, your taxon could end up >meaningless 
or paraphyletic.

>Recall: Allosauridae = { +_Allosaurus_, +_Acrocanthosaurus_}

>By your definition, if the tree topology read (_Metriacanthosaurus_,
>(_Acrocanthosaurus_, (_Allosaurus_, _Yangchuanosaurus_)))), what >would 
your taxon be? You have the clade containing all four, MINUS >the clade 
formed by anchor taxa allos and acrocanth. What does this >mean? Are 
your included taxa just yang. and metria. (paraphyletic)? >Are all four 
included (despite your definition)? Is the taxon just >ignored as 
invalid? How do you resolve this?

>If you're making a stem-based taxon, IMHO you should use only one,
>generic-level inclusive anchor (the taxon included in the taxon >you're 
defining), and do not use node-based taxa as anchors in the >definition. 
For node-based taxa, do not specify exclusive anchors >(non-included 
taxa, eg: "more closely related to inclusive anchor >than to exclusive 
anchor").

This comes from a limited understanding of "stem"- and "node"-based 
nomenclature. My appologies. It means that I include Metria with Yang 
while disregarding Allo as close enough to establish relationships as 
close as has been assumed. Szech is based on scrappy details (teeth) and 
the referal of a much smaller skeleton based on proximity is not enough 
to regard it as Szech, and I do not suggest it is Metria. 
Metriacanthosauridae _incertae sedis_ is more like it. Because of the 
details actually referable to Szech undeniably (the type and nothing 
else but more teeth that don't include the new specimen) I would also 
call him _incertae sedis_.

So, Metriacanthosauridae: Metria + Yang, their closest common ancestor, 
and all descendants thereof.

The details considering Sin and Yang are not close enough to justify the 
family. A rediscription, in my mind, is in order. Now, for one, 
*Marshosaurus* and *Monolophosaurus* all have pelvises more similar to 
Sin than to Yang, in that Yang's pubis is more robust and lacks a "foot" 
as developed as Sin's, and are related in themselves to each other by 
structure of their dentaries as opposed to those of other allosaurs.

Below is a temporary clade that can explain these ideas and their 
cladistic relationship associated with them. Because of the degree of 
differentiation between these internal dinosaurs, I've felt the need to 
develop new taxonomic groups to better differentiate them, with the 
earliest (i.e., more primitive) ones closer to the top of the tree. ? = 
represents _incertae sedis_.

o-ALLOSAURIFORMES
| |
| \__ALLOSAUROIDEA = Cryolophosaurus + Allosaurus
|
o-METRIACANTHOSAUROIDEA [SINRAPTOROIDEA]
|
|__Marshosaurus
|  |
|  |_?_Monolophosaurus
|  |
|  \__Sinraptor
|
o-METRIACANTHOSAURIDAE
|
\__Metriacanthosaurus
   | |
   | \__Yangchuanosaurus
   ?
   |__Szechuanosaurus
   |
   \__"Szechuanosaurus"?

This means *Marshosaurus* is closer to *Yangchuanosaurus* than to 
*Allosaurus*, and thus redistributing the tree slightly. 
*Cryolophosaurus*, more derived and later than *Allosaurus*, is a branch 
that derived from a form earlier in the record than allosaurids or 
metriacanthosaurids [sinraptorids], or derived from *Piatnitzkysaurus* 
parallel to *Marshosaurus* or derived from just such a taxon. I will 
note that this tree is not exact and that my definition of such is not 
is not as would be had from more professional descriptions arriving from 
published authors. I've had to invalidate several of my theories in the 
workings of this, when I first though Monolopho wasn't an allosaurian, 
but closer to basal coelurosaurians or even megalosaurs, but was proved 
wrong when I compared data with *Marshosaurus*. Imagine my surprise. So, 
I lost, but I gained, so this was not formed through just my "feelings".

I am in the process of gathering and shaping the data here plus a few 
others and will post them in a slightly different way that you or the 
list are used to seeing. This is mostly what I've arrived at through 
Tom's suggestions of how he'd like to see my definition of the 
Allosauria. I am open, like I said, to gun fire. :-)

Jaime A. Headden

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