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Re: Coelophysis *feathers*???



On Tue, 30 Jan 2001 10:31:35  
 Waylon Rowley wrote:
>
>
>
>To: Rob Gay
>
>
>>Personally, I feel that feathers are probably a very basal characteristic 
>>of theropods (I'll explain further down here). _Tyrannosaurus_ is well 
>>within the group conisdered to have feathers, as judged by phyogenic 
>>bracketing. But _T. rex_ shows no sign of feathers. But, it's more than 
>>likely that _Tyrannosaurus_ infants had feathers for isulation, that were 
>>later shed as the animal grew.
>
>Well, last I heard we only have preserved skin from the base of a tail and 
>under the throat for Tyrannosaurids. Birds have scutes AND scales, so I see 
>no reason why a tyrannosaurid might have a rim of feathers along its back, 
>or display feathers on its snout (rugose nasals? hmmmm....)

Do you really think so?  I think that most would be in agreement that 
Tyrannosaurus did not possess a complete body covering of feathers as an adult. 
 I do agree with Rob that the infant hypothesis is a good one, however, I don't 
know if it is "more than likely."  There is simply no evidence that 
Tyrannosaurus hatchlings possessed feathers, although I think that it 
definitely was probable.

However, a rim of feathers along its back...  This may be a possibility.  I see 
only two general functions for feathers within the tyrannosaur lineage: 
covering for juveniles and display features.  Using feathers as a complete body 
covering would be absurd in a large dinosaur that did not need insulation.  The 
feathers along the back hypothesis is intriguing, and I have heard it before.  
For me, it is easier to envision a tyrannosaur with a feathery crest or fan.  
Possibly, these crests were used as recognition features or as sexual display 
features, and maybe, (real speculation here), could have been sexually 
dimorphic between males and females.  

Generally, though, I have enjoyed reading this discussion.  I do believe that 
both time and actual phylogenetic relationships have to be taken together when 
determining the ancestry of birds, feathers, and other features.  Obviously, 
feathers evolved long, long before Sinosauropteryx and kin lived.  However, 
Zhexi Luo and his colleagues have proposed that the Yixian Formation actually 
preserves a biological refugium for relic species.  Perhaps, if these feathered 
dinosaurs were living in the current Liaoning refugium area some 120-125 mya, 
then perhaps they were much older, and maybe first evolved 130 million years 
ago...  I don't know, this is more speculation.  But, Luo and his team believes 
that the Yixian does preserve a refugium, and the specimens dated to 120 
million years old were actually living as relics.  The more we push back these 
dates, the closer we get to Archaeopteryx.  Of course, we can't push the 
Liaoning dates back far enough to the Early Jurassic (or Late T!
!
riassic...) when birds likely evolved, however, the dates are getting closer...

And, yes, I do look forward to the day when we find a Yixian-caliber Early 
Jurassic site!

Steve

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