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RE: did Jurassic dinosaurs have feathers?



> From: Tim Williams [mailto:twilliams_alpha@hotmail.com] 
> 
> I wonder if the Type I/II/III inference system may be a 
> little wobbly when it comes to dinosaur integument, given 
> that the concept of phylogenetic bracketing might be strained 
> for two reasons: (1) the frequency of reversals; (2) the 
> sheer rarity of taxa that have any integument preserved at all.  

Let's not forget that the levels of inference don't say "no bloody way
possible": they are simply degrees of security or confidence in particular
hypotheses. So:

Type I = pretty damn secure, and if you argue that the predicted condition
was absent in a given form without any support, than you are almost
certainly wrong. (Example of this would be people illustrating scaled-only
_Velociraptor_ in this day and age...)

Type II = ambiguous. Dealer's choice.

Type III = speculative. In the absence of any other supporting evidence,
probably a bad idea... (For example, putting protofeathers on _Diplocaulus_
or _Eryops_...)

> One possibility (definitely Type III = no bloody evidence at 
> all!) is that a fuzzy body covering is primitive for 
> Ornithodira, and was retained by certain pterosaurs (like 
> _Sordes_ etc) and dinosaurs (especially small theropods), but 
> lost (or scaled back) independently in many lineages.

Not unreasonable if and only if the elements on pterosaurs are homologous to
feathers. Given that there are reasons (as discussed in Unwin's popular
audience book) to suspect that this is NOT the case (and that they are
different in terms on developmental form and dermal origin), I'm less
supportive of that idea than I once was. Of course, this is subject to
revision for (among other things) demonstrating that pterofuzz does show to
be developmentally and structurally comparable to protofeathers.


Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA