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Re: Status of _Caudipteryx_



Alessandro Marisa wrote-

> I've compared only the ilium of Microvenator, Caudipteryx, and Nomingia,
but
> for me the ilium of Microvenator morphologically is similar to that of
> Deinonychus than those of Caudipteryx, which for me has an ilium in part
> similar to that of Nomingia.

Well, I'll save the reasons Caudipteryx falls out below Microvenator for the
end of the message and address your ilial characters first.

> Infact, the preacetabular region of Microvenator's ilium is shorter than
the
> postacetabular region as in Deinonychus (either AMNH 3015 Ostrom 1969 and
> MCZ 4371, Ostrom 1976), while in Caudipteryx the preacetabular region is
as
> long as (or longer) the postacetabular region similar to that of Nomingia
> (if longer) and others Oviraptorids.

The postacetabular process of Microvenator actually isn't preserved in
either ilium (Makovicky and Sues, 1998).  Using the postacetabular estimate
in that paper gives a preacetabular/postacetabular ratio (measured from the
anterior and posterior edges of the pubic and ischial peduncles
respectively) of .76.  This compares to .98 in Caudipteryx, 1.11 in
Nomingia, .73 in Ingenia and 1.00 in "Rinchenia".  Deinonychus (MCZ 4371)
has a ratio of 1.39 (note AMNH 3015 is "fragmentary and poorly preserved"
with an "unknown anterior margin").  This is similar to some other
dromaeosaurids (Unenlagia- 1.57), but others have ratios similar to
oviraptorosaurs (Bambiraptor- .81; Achillobator- .93; Adasaurus- .93).  As
you can see, Microvenator's preacetabular process is (probably) similar to
both Ingenia's and Bambiraptor's in length.  Some dromaeosaurs' are longer,
some oviraptorosaurs longer yet and other dromaeosaurs even longer.  This
does not seem to be a phylogenetically useful character.

> In Microvenator the fossa for the
> origin of the M. cuppedicus is large and deep as in Deinonychus and others
> Dromaeosaurids, while in Caudipteryx and Nomingia the fossa is very
shallow
> or absent as others Oviraptorids.

Microvenator does have an unreduced M. cuppedicus fossa, but dromaeosaurids
(Velociraptor- Norell and Makovicky 1997; Unenlagia- Norell and Makovicky
1999) do not.  Theirs are reduced, just like Caudipteryx and oviraptorids.
If you still want to have the phylogeny (Dromae (Micro (Caudi + Ovirap))),
this will still require a reversal for Microvenator (or independent
acquisition in dromaeosaurids), just as it would in my phylogeny of (Dromae
(Caudi (Micro + Ovirap))).  The character is therefore equivocal.

> Caudipteryx and Nomingia has a deep
> preacetabular region that tapers ventro-anteriorly and extends as
ventrally
> as the pubic peduncle in Caudipteryx and a half of the pubic peduncle in
> Nomingia, but in Microvenator the preacetabular region extends ventrally
> only 1/4 the pubic peduncle as in Deinonychus.

Actually, the ventral tip of Microvenator's preacetabular process is broken
off.  Following the outline of the bone to a point (as is shown in Makovicky
and Sues 1998) shows that it extends ventrally about halfway (51%) past the
pubic peduncle, as in Nomingia.  Ingenia's extends a third of the way, while
"Rinchenia's" and Caudipteryx's extend past the pubic peduncle.  This
doesn't seem to hold up to scrutiny either, as Microvenator is right in the
range of variation for oviraptorosaurs.  As a side note, some dromaeosaurids
(Deinonychus, Velociraptor, Unenlagia) have preacetabular processes that
extend a third or less of the way, but others (Bambiraptor) have ones that
extend ventrally past the pubic peduncle.  This character seems
phylogenetically useless as well.

As for why Caudipteryx is more basal than Microvenator and other
oviraptorosaurs in my analysis, Microvenator shares the following three
characters with caenagnathids and oviraptorids that are absent in
Caudipteryx-
dorsal posterior dentary process subequal to or deeper than ventral process
medial ridge on dentary
nearly all caudal vertebrae have transverse processes
Not many, but it's always most parsimonious.

Mickey Mortimer