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Re: Alvarezsaurs/Ornithomimosaurs (was Re: T. bataar)
Ken Kinman wrote:
<Well Patagonychus [sic] is a nice intermediate between
"something" and mononykines, but I'm not convinced that
Alvarezsaurus is that "something".
Seems to me it would be more prudent to put Patagonychus in a
Family Mononykidae, and obviously Alvarezsaurus goes in
Two separate families, two separate OTUs----at least until we
have more of an Alvarezsaurus skeleton to work with. In my
opinion somebody really jumped the gun in dumping these all into
one family, which is something a "lumper" like me rarely says.>
You, a lumper? Hah, I'd want to lump half the hadrosaurs, I
think they are totally oversplit; same for several groups of
sauropods. I'd also lumb Deinoncyhus and Velociraptor, never
formally name Rinchenia, and do tons of other stuff if I could.
Or I could substantiate my opinions.... There are also some
species I'd split off, too....
However, Chiappe et al. (1996: _Mem. Queensl. Mus._ 39, 3,
557-582) provided a matrix that suggested to him, substantiating
earlier Perle et al. (1993a: _Nature_ 362, 623-626; 1994:
_AMNovit._ 3105, 29pp) then Novas (1996: _Mem. Queensl. Mus._
39, 3, 675-702; and 1997: _JVP_ 17, 1, 137-166) that these are
all close enough to each other and that *Alvarezsaurus*, no
matter how bizarre it seems, is the most basal member as based
on a number of autapomorphies, which include: cervicals bear
craniocaudally short and dorsoventrally low neural spines (this
appears to be a functional character related to long and slender
necks in small animals, pers. obs.); sacrals and caudals
procoelous (also in some titanosaurs, but this is irrelevant,
they're not sauropods); posterior sacral centra transversely
compressed; first manal digit bears a broad, robust claw (which
differs enough from ornithomimosaurs or other "robust-clawed"
forms for field identification of isolated elements); no fossa
for the _M. cuppedicus_ (also in oviraptorosaurs and
therizinosauroids); supracetabular crest wide (funny enough,
most maniraptoriforms lack this, as do birds, or at least some
maniraptoriforms have very narrow crests, so this is a
diagnostic reversal); no posterior trochanter (not sure, but a
few other maniraptorans might also lack this, such as
oviraptorids, but it's present in *Chirostenotes* and you really
don't seem to tell in *Alxasaurus,* the thing is so crushed).
There's a few others listed, but these appear to be diagnostic
of a larger group, such as Maniraptora (narrow iliac pubic
peduncle, peduncle faces cranioventrally, ventrally curved
postacetabular blade) -- this listing is from Novas, 1996.
Probably most diagostic in alvarezsaurids is the forearm, to
which degree *Alvarezsaurus* is mildly comparable, including the
strong ventral angle of the proximal portion of the scapula to
the shaft and the resultant angling of the coracoid, which is
not how the coracoid angle becomes narrower in higher birds; the
forelimb bears a very large and robust claw; the caudals are
procoelous and the sacrals at least have a large caudal condyle,
instead of a cotylus as in most other archosaurs. Other
connective features are in press, so I'd better not say anything
further on them, but there are more.
No, for all intents and purposes, *Alvarezsaurus* is a basal
member of an exclusive taxon comprising it, *Patagonykus*,
*Parvicursor*, *Mononykus*, *Shuvuuia*, and the American form
(Hutchinson and Chiappe, 1998: _JVP_ 18, 3, 447-450), which is
not complete enough to designate a taxon after. What seems
certain is that the topology (*Alvarezsaurus* + (*Patagonykus* +
(*Parvicursor* + *Mononykus* + *Shuvuuia* + NA form))) is
correct. Their placement among theropods is more contentious.
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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