Re: Gobi finds

[pjanke@maroon.tc.umn.edu]

NEIL@ARC.UG.EDS.COM wrote:

>>       --six skeletons of the recently discovered creature Mononykus,
>
>Is this another find with feathers?  Or is the assertion based on anatomy?  
>How do they compare with Archeopteryx?

Mark Norell et al cites the following characters to place Mononychus 
"firmly in the group with other avians":

        - a breastbone with a strong median keel
        - a fibula reduced to a small spike
        - fused wrist bones.
        - a birdlike pelvis

On the other side, many and perhaps most scientists who look at this 
evidence notice the following about Mononychus:

        - it completely lacks wing structures
        - it has teeth
        - it has a long tail
        - it's footbones are not fused
        - it looks much less like a bird than _many_ groups of birds that 
          predate it in the fossil record, as well as it's own truly-avian 
          contemporaries.

The breastbone was probably the best case you could make for Mononychus 
being as avian as Archaeopteryx, but since the latest Archie fossil 
has a breastbone you can forget about that one. In addition, some 
paleontologists have suggested that Mononychus has forelimbs similar 
to some digging animals. Moles and other diggers also have keeled sternums.
Even Norell has said "much of the skeleton looks pretty average for a 
small theropod".  

It would be difficult for me to understand why Norell would insist this 
is a bird had I not seen NOVA, Dinosaurs of the Gobi. For those of you 
that haven't seen this, it contains a classic example of an over-reaching
conclusion being drawn from a cladistics model. 
[I can elaborate on this if anybody's interested]

---
>``We're picking up ... an extraordinarily rich picture of a
>dinosaur community toward the end of the dinosaur empire, that
>captures both the decline of the dinosaurs and the ... rise of the
>diversity of mammals,''

>Does anyone know more of this?  Are they saying (like Bakker) that the D's 
>were in decline at
>this time and we are seeing a faunal pattern which presages an
>end, or is it just "shortly before XXX wiped them out"? (let XXX be your
>favourite catastrophe)

They have no grandiose theory or deeper meaning here. I think they mean 
that they are getting some cool new fossils of these groups in these 
time frames.

>How close are the mammals to post Cretaceous finds?

Because of the pattern of blood supply to the brain, they've concluded 
that the mammal assemblage found in the Gobi are off the main branch of 
mammals of today. The used CAT scans to analyze several mammal skulls 
found on these expeditions to arrive at this conclusion.