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Re: Ah ha! That's where therizinosaurs came from



Jaime Headden <qi_leong@hotmail.com> wrote:

>   I like to think of *Oviraptorosauria* as a clade (*Oviraptor philoceratops* 
> Osborn, 1924 < *Passer domesicus* Linnaeus, 1758) [including the first, 
> excluding the last -- although a more complete listing would use a few more 
> exclusive specifiers]. If so, it would automatically include anything that 
> could find its way into a sister-group relationship with "basic" 
> oviraptorosaurs.

Sorry, I should have been more precise. Xu et al. (2010) argued for a
sister group relationship between scansoriopterygids and the least
inclusive clade containing all taxa currently regarded as
oviraptorosaurs.

>   This would mean coining new names for the internal "former 
> oviraptorosauria" clade, but that's a non-issue: We can easily coin a name 
> for each major node in the stem's content (by which I mean robustly supported 
> and non-labile, supported by most divergent analyses), and clade 
> (*Scansoriopteryx heilmanni* Czerkas & Yuan, 2002 + *Oviraptor philoceratops* 
> Osborn, 1924) would be one of these. Cau's "greater Oviraptorosauria" 
> suggestion would require instead treating the classic name as a node, so that 
> adding taxa as sisters to the clade would allow one to name more and more 
> external nodes. The stem idea is very useful and effective, and I see no 
> issue with departing from it.

I agree that when a phylogenetic hypothesis changes, it is the content
of a name that should change accordingly, not the definition. When Ken
Carpenter found _Scelidosaurus_ to be an ankylosaur in 2001, he did it
the other way around: he replaced _Ankylosauria_ with
_Ankylosauromorpha_ and restricted the former name to a less inclusive
node-based clade. I think it was a wrong decision. However, I have to
admit that if any future analysis finds a clade consisting of
"traditional oviraptorosaurs" (_Protarchaeopteryx_ + _Oviraptor_),
scansoriopterygids and/or sapeornithids, I will be quite happy to call
it "Magnoviraptorosauria".

>   Xu et al. is only a recent analysis [...]

I am not sure what Xu et al.'s analysis you are talking about. If you
mean their recent paper on _Xiaotingia_, I don't see how it is
relevant to the relationships of oviraptorosaurs. They mention many
similarities of oviraptorosaurs and basal avialans, but they also note
that it is more parsimonious to place oviraptorosaurs in their usual
position as a sister group of _Eumaniraptora_. (Actually, they say
_Paraves_, but that is a tautology.) Their 2010 paper I cited was not
an analysis; the authors just presented a topology and listed derived
characters that support it.

>   Based SOLELY on the postcranial anatomy, I find (as I did when I conflicted 
> with Mickey WAAAY back in 2002 when we were competitively ratcheting our 
> analyses) scansoriopterygids likely to be non-avialaeans.

What do you think about Agnolín & Novas (2011) analysis, then? It used
a modified version of the TWG matrix and (surprisingly...) supported
Novas's pet hypothesis -- avialan unenlagiines -- but it also pulled
scansoriopterygids out of _Avialae_ and _Eumaniraptora_. I wonder if
future TWG analyses will incorporate their changes to the coding.
Also, it would be interesting to see what would happen if someone
added _Xiaotingia_ into their matrix.


References:

Agnolín FL, Novas FE 2011 Unenlagiid theropods: are they members of
the Dromaeosauridae (Theropoda, Maniraptora)? An Acad Bras Ciênc
83(1): 117–62
http://www.scielo.br/pdf/aabc/v83n1/v83n1a08.pdf

Xu X, Ma Q-Y, Hu D-Y 2010 Pre-_Archaeopteryx_ coelurosaurian dinosaurs
and their implications for understanding avian origins. Chin Sci Bull
55: 1–7
http://www.springerlink.com/content/387524025j71h741/fulltext.pdf
-- 
David Černý