[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Most dinosaurs were scaly

Not to be too harsh, but you rather completely ignored my objection regarding 
body size.  Do the authors take this into account?  Do you think it's 
worthwhile?  As I said before "In other words, it's obvious if you just plug in 
known skin coverings 
over a cladogram, scales will be the ancestral state for Dinosauria."  If all 
the authors do is test a hypothesis based on faulty assumptions to find an 
answer we all know would be found, then I fail to see how it could be the best 
poster at SVP.

Mickey Mortimer

> Date: Mon, 30 Dec 2013 15:45:16 -0800
> From: pristichampsus@yahoo.com
> To: dinosaur@usc.edu
> Subject: Re: Most dinosaurs were scaly
> I found this to be the best poster at SVP this year. Ever since the discovery 
> of structures associated with Tianyulong and (to a lesser extent) that one 
> Psittacosaurus individual, there seems to be a growing trend in dinosaur 
> paleontology to assume that all dinosaurs were filamented (all ornithodirans 
> even), in spite of a large collection of scale impressions from all major 
> lineages. Barrett and Evan's analysis represents an actual test of this 
> hypothesis. That neither parsimony analysis nor max likelihood (the latter of 
> which is more amenable to reversals) found filaments to be ancestral to 
> dinosaurs suggests that ancestrally scaly dinos is still the most 
> parsimonious explanation. Admittedly, without data on the tree support values 
> (available for the max likelihood tree at least) or a more detailed look at 
> the methods we can only say so much about these results.
> I would caution against arguments for unique scale-filament intermingling, 
> based on hair distribution in armadillos. Armadillo "scales" are not actually 
> scales but are a unique form of agglutinated hairs (Wu et al. 2004). 
> Pangolins are even weirder as their armour seems to have evolved from the 
> same germinative layers as claws/nails (Spearman 1967). In fact, according to 
> evo-devo studies synapsids probably never had "true" scales (= sauropsid 
> type) as beta-keratin (a
been found in the integument of mammals (although pangolins do have an 
> As for whether we might be mislead into thinking some pebbly skin texture is 
> actually scaly, it is a cause for concern. Dinosaur skin impressions tended 
> not to receive much description unless they involve filaments. It has only 
> been rather recently that there has been an interest in the scaly coverings 
> of dinosaurs, with Bell (2012) and Davis (2012) offering insights into scale 
> structures and distribution among dinosaurs. Paik et al. (2010) gave the only 
> analysis I'm aware of regarding potential misinterpretation of lithological 
> structures as being integumental,
> can occur. A key factor to determining scales vs. lithology (or pebbly skin) 
> seems to be the regularity of the structures. Pebbly skin has raises and 
> cracks that are randomly distributed. Similarly, rainprints and ripple marks 
> may be more uniform but don't interlock and often vary greatly in size from 
> print to print. Scaly skin, on the other hand, tends
> to show a more regular patterning of interlocking polygons.
> It's unfortunate that this is only a press release. I talked with Paul at SVP 
> about this being coming out as a paper and he mentioned that it would be 
> published soon. It's too bad this press release may take away a lot of the 
> impact.
> Jason
> References
> Bell, P.R. 2012. Standardized Terminology and Potential Taxonomic Utility for 
> Hadrosaurid Skin Impressions: A Case Study for Sauroplophus from Canada and 
> Mongolia. PLOS One. 7(2):e31295.
> Davis, M. 2012. Census of Dinosaur Skin Reveals Lithology may Not Be the Most 
> Important FActor in Increased Preservation of hardorsaurid Skin. Acta. 
> Paleontological Polonica.
> Paik, S., Kim, H.J., Huh, M. 2010. Impressions of Dinosaur Skin from the 
> Cretaceous Haman Formation in Korea. Journal of Asian Earth Sciences 
> 39:270–274.
> Spearman, R.I.C. 1967. On the Nature of the Horny Scales of the Pangolin. 
> Journal of the Linnean Society (Zoology). 46(310):267–273.
> Wu, P., Hou, L., Plikus, M., Hughes, 
 Suksaweang, S., Widelitz, R.B., Jiang, T-X, Chuong, C-M. 2004. Evo-Devo of 
Amniote Integuments and Appendages. International Journal of Developmental 
Biology. 48:249–270.
>> From: Zach Armstrong <zach.armstrong64@yahoo.com>
>>To: "dinosaur@usc.edu" <dinosaur@usc.edu>
>>Sent: Saturday, 28 December 2013 4:53 PM
>>Subject: Re: Most dinosaurs were scaly
>>I concur with what Mickey has said. I would also like to raise the question 
>>of how confidant we can be that the all the scales of dinosaurs are true 
>>scales, and are not epidermal structures secondarily derived from feathers 
>>due to evo-devo mechanisms?
>>At least some evo-devo studies suggest that the reticula scales on the 
>>plantar surface of avian feet are actually developmentally stunted feathers. 
>>To quote from Dhouailly (2009), "[R]eticula are not true cutaneous 
>>appendages, and appear to be feathers
>>arrested in the initiation step of their morphogenesis: formation of a
>>slight bump, without a pla
> lar suggestions were made by Sawyer and Knapp (2003).
>>At least some non-scale epidermal structures in modern avians morphologically 
>>mimic scales too. For instance, the facial wattles of Philepitta schlegeli 
>>(Schlegel's Asity) have an appearance to me that mimics scales: 
>>A similar thing can be said about the bare skin on the head and neck of 
>>Coragyps atratus (Black Vulture): 
>>If all we had were fossilized impressions of these bare skin structures, 
>>might we erroneously conclude they were true scales?
>>I also think inferring from osteoderms in thyreophorans and sauropods that 
>>their ancestors never had filamentous integumentary appendages (FIAs) might 
>>be misleading. Hair sprouts amongst the osteoderms of armadillos for 
>>Do fossil cingulates
derms? Seems unlikely.
>>The same might be true for scaled dinosaurs, even those with osteoderms. 
>>Additionally, feathers erupt from scutate scales in some birds on occasion. 
>>Sawyer & Knapps (2003) noted, "The growth of feathers from the distal ends of 
>>scutate scales occurs occasionally in normally scaled [chicken] breeds such 
>>as White Plymouth Rock and White Leghorn.
>>have been observed growing from the tips of the definitive scale ridges at 12 
>>days of incubation." So scales and feathers intermingling are not de facto 
>>impossible, although there appears to be significant developmental 
>>constraints. Maybe these constraints were more relaxed during the initial 
>>evolution of FIAs in dinosaurs.
>>> From: Mickey Mortimer <mickey_mortimer111@msn.com>
>>>To: "dinosaur@usc.edu" <dinosaur@usc.edu>
>>>Sent: Friday, December 27, 2013 11:48 PM
>>>Subject: RE: Most dinosaurs were scaly
>>>Is it just me, or does this study seem to suffer fr
> aively assuming body covering doesn't covary with other factors we can test?  
> In other words, it's obvious if you just plug in known skin coverings over a 
> cladogram, scales will be the ancestral state for Dinosauria.  No one's ever 
> doubted that, Greg Paul included.  The additional factor which has been 
> discussed ever since his 1988 work is of course size.  What happens if you 
> only plot small specimens on the cladogram?  Ornithischians are all 
> fuzzy/spiny, and sauropodomorphs are unknown unless the titanosaur embryos 
> count.  Even if the latter do count, Sciurumimus makes theropods primitively 
> fuzzy despite Juravenator, so that's ambiguous basal Saurischia and fuzzy 
> basal Dinosauria, which only gets more support if pterosaurs are 
> avemetatarsalians.  Maybe Barrett and Evans include a caveat about this 
> assumption, but since taking it into account nullifies their entire 
> conclusion, I don't think
>>it could help.  This isn't even getting into the metabolic and growth 
>>evidence that
>>>shows increasingly basal archosauromorphs weren
>>>'reptiles'.  You might as well determine ornithischians don't have cheeks 
>>>based only on their lack in birds, crocs and lepidosaurs.
>>>Mickey Mortimer
>>>> Date: Fri, 27 Dec 2013 10:13:58 -0800
>>>> From: bcreisler@gmail.com
>>>> To: dinosaur@usc.edu
>>>> Subject: Most dinosaurs were scaly
>>>> From: Ben Creisler
>>>> bcreisler@gmail.com
>>>> A news item and the original abstract from the 2013 SVP meeting:
>>>> Nature news:
>>>> http://www.nature.com/news/feathers-were-the-exception-rather-than-the-rule-for-dinosaurs-1.14379
>>>> The abstract from the SVP Meeting:
>>>> Poster Session III (Friday, November 1, 2013, 4:15 - 6:15 PM)
>>>> BARRETT, Paul, The Natural History Museum, London, United Kingdom; EVANS,
>>>> David, Univ of Toronto at Mississauga, Toronto, ON, Canada
>>>> Osteoderms and scaly skin impressions are historically well known in n
> saurs
>>>> these structures,
>>>> many dinosaur taxa possessed other integumentary features, including a
>>>> range of ‘quills,'
>>>> filaments, and feathers in non-avian theropods and ornithischians.
>>>> Feathers and their
>>>> homologs are commonly regarded as a synapomorphy of either coelurosaurian 
>>>> or
>>>> tetanuran theropods, but some authors have gone further, using the 
>>>> presence of
>>>> ornithischian feather-like structures to suggest that these structures
>>>> are plesiomorphic for
>>>> Dinosauria. This inference has wide-ranging implications for dinosaur
>>>> biology and
>>>> evolution.
>>>> However, to date, no studies have attempted to assess rigorously the
>>>> evolution of
>>>> dinosaur integumentary structures within a broad phylogenetic context.
>>>> We compiled a
>>>> complete database of all epidermal integumentary structures reported
>>>> in dinosaurs, by
>>>> major body region, in order to investigate the origin of feather
>>>> homol
>>nd the
>>>> evolution of integumentary structures in the clade
>>>> definitively present in
>>>> virtually all major ornithischian clades. This, and the presence of
>>>> extensive armour in
>>>> thyreophorans suggests that genasaurian skins were primitively scaly. 
>>>> Similarly,
>>>> sauropodomorphs lack evidence for anything other than scales or
>>>> osteoderms. Fitch
>>>> optimization of integument types on dinosaur phylogenies shows that there 
>>>> is no
>>>> unequivocal support for inferring a deep origin of feather-like
>>>> structures, a result
>>>> supported by maximum likelihood ancestral state reconstructions for
>>>> these characters.
>>>> The structures in Tianyulong and Psittacosaurus are best regarded as
>>>> autapomorphic
>>>> integumentary modifications, and there is currently no strong evidence
>>>> that these features
>>>> are feather homologs. Further work on the chemical composition of
>>>> these structures, and
>>>> those in several non-coelurosaurian theropods, is needed. Although
>>>> ornithodirans exhibit
>>>> a range of integumentary novelties that may be related to the origin
> re currently the only dinosaurs that display unequivocal e
>>>> feathers and their
>>>> direct homologs.