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Re: Most dinosaurs were scaly



"Again I cite Yutyrannus as an example of why, but one can also look at the 
general patterns of integument we see in extant taxa too. It's not just that 
Yutyrannus shows no loss of filaments with its large size, it's that it shows 
no scales on its hide either.”

Neither do a vast majority of ornithodiran specimens from lagerstatten/fine 
grained sediments, including euornithean bird feet, hadrosaur hides, etc. Were 
these all secondarily bare skinned? Obviously there is a sedimentological bias 
against scale preservation in fine-grained shale, at least in larger-boies 
animals (scale preservation in lizards and choristoderes in the same sediments 
seems marginally more common).

The hypothesis that Yutyrannus independently evolved a more extensive feather 
covering and that other tyrannosaurs retained scales elsewhere on the torso is 
just as parsimonious as the hypothesis that… what’s the alternative you’re 
suggesting? That Yutyrannus is not a tyrannosaur and tyrannosaurs are scaly 
non-coelurosaurs? If you contend that eve/devo says it’s all or nothing 
feathers or scales and the ancestral feathered animal was feathered head to 
toe, than Yutyrannus must be closer to birds than to Gorgosaurus, right? I’ve 
heard people suggest that Yutyrannus is actually related to carcharodontosaurs 
but never that it’s more derived than tyrannosaurs among coelurosauria.

You said elsewhere that you would consider this strict interpretation of 
eve/devo falsified if an unambiguous fossil is found showing both feathers and 
scales present on areas other than the leg. Time will tell on that one, but I 
don’t think it’s at all justified to assume the developmental all-or-nothing 
pathways seen in crown birds is necessarily the ancestral condition and has 
remained unmodified for the past 165 million years of pan avian evolution.

Matt


On Dec 31, 2013, at 1:56 AM, Jura <pristichampsus@yahoo.com> wrote:

>> From: "Thomas R. Holtz, Jr." <tholtz@umd.edu>
>> 
>> Actually, Mickey's objection wasn't. His objection was that if you only
>> coded small-bodied animals. The presence of large-bodied animals with fuzz
>> is a different issue.
> 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
> I don't think that size is quite the problematic factor that Mickey is 
> portraying it to be. Again I cite Yutyrannus as an example of why, but one 
> can also look at the general patterns of integument we see in extant taxa 
> too. It's not 
> just that Yutyrannus shows no loss of filaments with its large size, 
> it's that it shows no scales on its hide either. A common misconception that 
> I 
> see on this list and elsewhere is that scales are not a form of 
> integument, but are instead equivalent to bare skin. Yes large 
> extant mammals show hair loss (or rather skin area outpacing hair formation) 
> with larger
> body size, but they DON'T replace their hairless regions with scales. 
> Similarly, ostriches lose leg and neck feathers as they reach adult 
> size, but they NEVER replace these bare areas with scales. There are no 
> scales in the apteric regions of birds. Scales only ever occur on the 
> tarsometatarsus in birds. There is now an abundance of evo-devo 
> literature out there that suggests that there is a strong developmental 
> constraint behind this, and that even these small scaled areas of birds 
> are a relatively recent development (compared to feathers). The point 
> is: no extant animal today swaps one form of integument for another. Not
> with ontogeny, and only rarely, with phylogeny (i.e., it has to evolve 
> at some point). Even then, mixing and matching of integument doesn't seem to 
> happen. 
> 
> 
> So if we see scales on the non-metatarsal/feet regions of tyrannosaurids and 
> allosaurids (and we do), it means that it was most likely that these animals 
> were entirely scaly animals. If tyrannosaurids preserved bare skin like 
> Pelecanimimus seems to, then we could argue that filaments were reduced in 
> these taxa due to their large body size.
> 
> 
> ___________________
> 
>> And another issue ignored in this is that NOT ALL SEDIMENTS ARE EQUAL!
>> Optimize the same data for only lacustrine/lagoonal vs. coarser seds and
>> you get additionally different pictures.
>> 
>> Furthermore, a point I have made elsewhere: how well does fuzz/hair
>> fossilize in non-shale anyway? When we have skin impressions of larger
>> bodied Cenozoic mammals, how often do they show fur or hair?
> 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
> I'm not sure how often hair is preserved in these sediments, but even so, 
> naked skin is not scaly skin. It is what is found underneath/between scales, 
> hair, and feathers. We are comparing apples and oranges here.
> 
> That said, I am in agreement with you, Matt, and others in that a better 
> understanding of how sedimentology affects integument preservation would 
> prove most useful. It is something that is sorely needed now that preserved 
> soft tissue has become more prevalent in the fossil record. 
> 
> 
> Jason
>