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Re: Heterodontosaurid with protofeathers

Jeff Hecht wrote:

> I talked with Alan Brush who says the "protofeathers" were
> hollow unbranched structures, just as he and Rick Prum had
> predicted the ancestral form would be. I'm no expert, but
> it's looking plausible that some kind of filamentary fuzz
> might have been primitive within archosaurs after the
> crocodiles split off. Or perhaps before; it could be that
> the fuzz was easy to lose. 

Jeff, I agree.  At least to a large degree...


"One possibility... 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.  Under this hypothesis, sauropodomorphs would be secondarily 'naked'. 
 Most (and maybe all) ornithischians might be naked too - either due to large 
body size, or to a burrowing ecology in the smaller and/or more basal 
ornithischians.  The tail 'quills' of _Psittacosaurus_ could even be highly 
modified versions of these filamentous structures.  This hypothesis would mean 
that a fuzzy integument  would go back to lagosuchian-grade archosaurs.  Highly 
speculative, I know, and as I write this I find myself less and less convinced 
that it's even plausible."

As I re-read this, I find this idea slightly more plausible.  And with the 
caveat that we now have basal ornithischians (a heterodontosaur) with 

Although this topology is not supported in the _Tianyulong_ paper, a 
Heterodontosauriformes clade (uniting heterodontosaurids and marginocephalians) 
could make the integumentary structures of _Tianyulong_ and _Psittacosaurus_ 
synapomorphic for heterodontosauriforms and independent of theropods.