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Re: A few questions



Dino Rampage (dino_rampage@hotmail.com) wrote:

<1) I've recently seen illustrations in which Lambeosaurus lambei and L. 
magnicristatus have been shown to be female and male of the same species.
Is this generally accepted?>

  Not really. Presently, they are separated as different species, and
similarly sized skulls to "male" *L. lambei* have smaller, dimoprhic
crests in enough abundance to suggest *L. lambei* is qualitatively
dimorphic without *L. magnicristatus* material in there. Other suggestions
include the following hypothesis which indicates an evolution along two
trends: increasing size, and increasing cranial crest size:

  --+--Hypacrosaurus altispinus
    `--+--Hypacrosaurus sternbergi
       `--+--Lambeosaurus lambei
          `--Lambeosaurus magnicristatus

  Others have proposed a synonymy between *Hypacrosaurus* and
*Corythosaurus,* with *Lambeosaurus* as a unique taxon (Paul, 1988;
Wagner, 2001 PhD thesis), but the alternative above is the suggestion of
Horner et al., 1999, where C evolves into H evolves into L. *Corythosaurus
casuarius* and *Lambeosaurus magnicristatus* are the extremes and the
other are radially arranged along the spectrum.

<3) What is the current taxonomic status of the giant caenagnathid? Is it>
Chirostenotes pergracilis, a new species of Chirostenotes or a new genus? 

4) How does Chirostenotes pergracilis appear different from C.
sternbergi?>

  Answering both these at once. The first taxon is so far unplaced in an
institution and is thus being made unavaiulable to discussion for the time
being. Fortunately, there are people looking at it right now, so we can
hope, hope, hope.

  Mickey already indicated what actually separates *C. sternbergi* from
*C. pergracilis*. The lower jaws are unique, and there are two morphotypes
known from the Dinosaur Park Formation, both of them having been indicated
as *Chirostenotes cf. sternbergi*. However, the jaws cannot be referred to
the holotype articular region of the lower jaw except by size; that there
are two different species represented in the material makes the question
of referral in much doubt. This includes Sues' referal of the material to
*Elimisaurus elegans* (based on postcrania), or Varricchio's support of
this referal.

  In other words, there are about four present unresolved specimen groups
in the Dinosaur Park Formation referable to the Caenagnathidae. The giant
oviraptorosaur is a caenagnathid and comes from the Sandy Site of the Hell
Creek Formation, and has a much more unique jaw than any other species.
There is previously identified material of this taxon from elsewhere in
the Hell Creek, but this will await description. The specimens consists of
two conmingled specimens that share cranial and postcranial material (no,
they are not Siamese twins...) and there are elements from all parts of
the skeleton, including caudals, dorsals, ribs, gastralia, complete
pelvises, pectoral girdles including furculae and sternals, and the
braincase and snout of the skull. More to come ...

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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